Ionic contamination PCB
Ionic contamination issues arise due to the ionic residues left behind during PCB fabrication and assembly processes. These residues can be plastic, metal, and fiberglass granules, including salts, oils, and dust. These ionic residues have a zero net charge (the composition of positive cations and negative anions) and become charged when a PCB passes through multiple fabrication processes. During assembly, the components also carry various ionic/conductive contaminants along with cutting oils/fluids, biocides, and corrosion preventatives. How do we handle circuit boards in the production line is also a major cause of ionic contamination in a PCB. In this article, you could learn everything about ionic contamination in PCB. Check and read the content below for more knowledge about it.If you want to order PCB product, please check and custom your order online. What are the sources of ionic contamination in PCB? Ionic contamination may occur during PCB fabrication and assembly processes. During fabrication, the creation of PTHs, etching process, and drilling are responsible for the contamination. On the other hand, during assembly, flux residue in soldering, component biocides by pick and place machine, and ionic surfactants from solder preparation are responsible for PCB ionic contamination. Read the post on component placement guidelines for PCB design and assembly. · Moisture trapped in PCB layers: Ionic contaminants in contact with moisture can increase short-circuit risk.· Etching chemicals: Chemicals used for PCB etching purposes are highly conductive and corrosive. It is essential to neutralize/rinse them since they can be a potential cause of leakage current.· Flux residues: Common conductive flux residues from the soldering process include various unreacted activators, binders, rheology components, and saponifiers. These residues must be removed by using solvent cleaning, say vapor degreasing, or by aqueous chemistries in the common batch.· Inter-layer residues during drilling and plating (PTHs): Inter-layer residues generated during drilling and plating are also responsible for ionic contamination.· Improper PCB surface cleaning: The majority of ionic contaminants come from the board itself. Before placing components over the bare board, you need to ensure that no contaminant is left from the previous production step. What are the effects of ionic contamination in PCB? The occurrence of ionic contamination on PCB assembly can inhibit its performance. In the production house, bare boards can carry ionic contaminants in the form of left-over flux, etching chemical, and solder material. If these residues are left on the board, major issues, like Electrochemical Migration (ECM), corroded traces, parasitic leakages, and dendritic growth, can hamper the PCB’s life-cycle. Read 8 soldering tips to avoid possible ionic contamination issues. Electrochemical migration (ECM): Electrochemical migration is caused by the electric field in which metal gets dissolved, resulting in ion formation between two copper features. If the electric field is applied, the metal dissolves at the Anode and gets deposited to the Cathode resulting in dendrite growth. Because dendrites grow from conductive ions, they can direct PCB currents differently from what is intended, leading to short circuits. Dendrites create alternative current paths that can affect the accuracy of current measurements in a PCB. Corrosion: Usually, PCBs corrode due to their material. Ionic contamination can corrode the entire PCB in a much shorter time. When ionic residue comes in contact with moisture, the short-circuit risk increases. The corroding metal flakes off, overlooking the chemical properties needed for the PCB product to operate correctly. Selecting apt PCB material and laminates helping with ionic contamination issues. Ionic contamination alone is not responsible for the above consequences; moisture and environmental exposure are also. That is why PCBs are baked to eliminate moisture before starting any new process. The ionic contamination level needs to be controlled during the manufacturing of circuit boards by adopting a process control tool. This tool ensures that the individual production process steps (e.g., surface-mount or through-hole) are performed in a controlled manner to achieve a manageable ionic contamination level. What is text of ionic contamination in PCB? Bad quality control during PCB fabrication, component placement, and a sub-standard final cleaning are some of the major issues responsible for ionic contamination. It is crucial to identify, control, and mitigate such issues. This can be done with proper ionic contamination testing equipment and analysis. ROSE testing, ion extraction, and ion chromatography are some of the well-known methods. Sometimes, humidity validation testing is also performed at the beginning of the production. To ensure the life-span of the PCB, testing of the bare board for ionic contamination prior to assembly reduces the risk of defects caused by contaminants. Ionic contamination testing is performed to detect ionic residues resulting from the fabrication and soldering steps. Let’s have a detailed analysis of cleanliness testing methods for the determination of ionic contamination. What are the benefits of measurement of ionic contamination in PCB? The PCB sample dipped in an extraction solution releases ions with an extraction liquid, which is determined by a conductance detector. The final result is calculated by an ionic contamination meter with the help of software. The measurement value is analyzed with reference to sodium chloride. Benefits: · The cleanliness measurement is ideal for post soldering evaluation as per official regulation. Also, it verifies surface quality prior to PCB coating and other chemical processes.· The testing also performs quantitative determination of the ion contaminates for PCBs in µg/cm² equivalent NaCl.· The cleanliness measurement continuously monitors contamination of quality through regular sample-based measurement.Wanna know PCB knowledge? Check and read for more.
PCB Glossary ⋅ 08/16/2021 10:22
DRC in PCB
A design rule check is a set of rules used by a designer to ensure the schematic matches all manufacturing considerations and dimensional tolerances set for a board. Production processes have a margin of error for the variation in the products that are manufactured. Such variations in production yield are adjusted in the design phase itself. In this article, we will focus on the topic and you can learn more knowledge from the content below.If you want to order PCB product, please check and custom your order online. What are the rules of DRC in PCB? Electronic design automation software lets you know when a design margin is violated by stating the parameter that is out of the acceptable range. This is called a DRC error and it helps eliminate rework in the production stage. DFM rulesDFM stands for design for manufacturing, which is the layout topology in a way that avoids all the problems that could be encountered during the PCB fabrication and assembly processes. Drilling checks for drilling holes:Drill-to-copper: The drill-to-copper is the land clearance between the edge of a drilled hole to the nearest copper feature. The nearest copper feature can be a copper trace, copper pour, or any other active copper region. What is a Pad in PCB Design and Development? Annular ring checks: To achieve acceptance for Class 2 and Class 3, follow the tables below published by Altium. The first one gives the annular ring requirements for mechanically drilled blind, buried, and through-holes on ½ oz copper: What is DRC and LVS check?A DRC allows one to verify the schematic and layout with regard to the margin of error you can incorporate in your design. As it allows one to check if a specific board layout correlates with the original circuit diagram or schematic of the design, it is also called layout versus schematic (LVS) check. What are DRC errors?Electronic design automation software lets you know when a design margin is violated by stating the parameter that is out of the acceptable range. This is called a DRC error and it helps eliminate rework in the production stage. DFM rulesDFM stands for design for manufacturing, which is the layout topology in a way that avoids all the problems that could be encountered during the PCB fabrication and assembly processes. Drilling checks for drilling holes:Drill-to-copper: The drill-to-copper is the land clearance between the edge of a drilled hole to the nearest copper feature. The nearest copper feature can be a copper trace, copper pour, or any other active copper region. Annular ring checks: To achieve acceptance for Class 2 and Class 3, follow the tables below published by Altium. The first one gives the annular ring requirements for mechanically drilled blind, buried, and through-holes on ½ oz copper: Signal checks: The first checklist we like to implement after receiving Gerber files is signal checks. This checklist holds key parameters that include conductor width, spacing requirements, hole registration, and many more. Solder mask checks: Coming to solder mask clearance, we can typically define it as a general isolation recommendation alongside specific details characterized by the kind of surface element(s) being isolated. Particular specifications apply to pads, which may be solder mask defined or non-solder mask defined, and drill holes, which may be plate through-holes or non-plated through-holes.Silkscreen checks: Silkscreen to mask spacing, silkscreen to copper spacing, and silkscreen to hole spacing and route spacing DFA rulesDFA is the process of designing a device or a PCB board by considering the ease of assembly as one of the key criteria. Here are a few DFA guidelines: Select readily available components and validate their production. This will prevent production delays. Apply component spacing guidelines. The component placement will determine whether the board can be assembled, the soldering techniques and the type of thermal dissipation to be used. Use component manufacturer recommendation for footprints. This will prevent pad mismatch while ensuring accurate markings for identification are present. Apply board edge guidelines. Board shape and component placement can impact panelization. DFF stands for design for fabrication. Therefore, as the name suggests, this addresses the issues related to fabrication. DFA stands for design for assembly. In most cases, DFF and DFA together make up DFM. DRC (resign rule checking) in many cases is used for DFM but is not sufficient. That’s also acceptable to some extent because DRC issues detected in manufacturing can indeed have a direct impact on the manufacturability of a PCB. However, DRC is different from DFA.Wanna know PCB knowledge? Check and read for more.
PCB Glossary ⋅ 08/16/2021 10:11
QFN stands for quad flat no-lead package. It is a leadless package that comes in small size and offers moderate heat dissipation in PCBs. Like any other IC package, the function of a QFN package is to connect the silicon die of the IC to the circuit board. In this passage, we will talk about the detailed knowledge of QFN package of PCB. Please check and read the content below we prepare for more information.If you want to order PCB product, please check and custom your order online. What is the structure of QFN package in PCB? The QFN packages come with a die that is surrounded by a lead frame. The lead frame is made up of a copper alloy with a matt tin coating. The die and the frame are usually connected to each other using wire bonding. Copper/gold is usually preferred for wire bonding. Some manufacturers use flip-chip technology for this interconnection. The flip-chip technique offers better electrical performance compared to the conventional one. The metalized terminal pads are located at the bottom surface. These terminal pads are present along the four edges of the bottom surface and provide electrical interconnections to the PCB. The bottom side of the package consists of an exposed pad. This pad provides an efficient heat path to the PCB. The exposed pad enables ground connection as well. The QFN package is soldered to the circuit board at the exposed pad. The die attach is the epoxy material used to fix the die to the exposed pad. For thermal management in PCBs, check out 12 PCB Thermal Management Techniques to Reduce PCB Heating. The following are some of the properties of standard QFN packages: · 0.35mm to 2.10mm maximum seated height (standard: 0.85 mm)· Terminal plating of Ni-Pd-Au and Sn· Halogen-free and lead-free· RoHS, ELV, and REACH compliance What are the advantages of QFN package? ·Quad flat no-lead packages come in lightweight and are easy to handle.·These packages are available in a thin profile and a small form factor.·The bond wires that are used to connect the die and frame are short.·The lead inductance of these packages is low.·They are ideal for applications that require good heat dissipation.·These packages are easily available at a low cost. What are the main types of QFN package? Based on the method of molding, the QFN packages are classified into punch-type and sawn-type packages. Punch-typeIn punch-type singulation, the package is molded in the single mold cavity format and is separated using a punch tool. This means that only a single package is molded into shape using this method. Sawn-typeThese packages are molded using the mold array process (MAP). This method involves cutting a large set of packages into parts. A final saw process helps to separate the sawn-type packages into individual packages. How to solder QFN on PCB? Soldering is a part of the QFN assembly process. During the assembly process, the components are mounted after solder paste screening. After QFN components are mounted using a pick and place tool, they are soldered using reflow soldering. When the PCB board goes into a reflow oven, the temperature inside will make certain areas of the board heat faster than the rest. The heavier components and large copper areas will take more time to get heated. The top surface temperature of the QFN package is monitored using thermocouples throughout the process. This is to check that the peak package body temperature (TP) does not exceed the standard values. How are the QFN solder joints inspected? The solder joints of the QFN components are formed underneath the package. Hence for the inspection of these, optical inspection and X-ray inspection are used. Rework on assembled componentsIf a defect is noticed post assembly on any QFN component, that particular component can be removed and replaced. Special rework stations are available for this purpose. A rework station should have the following components. · Split-light system: acts as a vision system to observe the bottom side of the package and the site on the PCB.· An X-Y table for alignment.· A hot-air system with top and bottom heaters for component removal. The procedure for rework is given below. · A pre-bake process is done before heating to avoid any moisture-related failures of the board and the components.· The next step is de-soldering and the temperature profile of the board and the components should be kept in mind.· Once de-soldering is done, the component should be mechanically removed. For large components, pipettes can be used and for smaller ones, tweezers are a good option.· After removal, the PCB pads should be cleaned to remove any solder residue. This also prepares the site for the new component placement.· The placement of the new component takes place through the same steps mentioned earlier during assembly.Wanna know PCB knowledge? Check and read for more.
PCB Glossary ⋅ 08/14/2021 09:37
Transmission line in PCB
Do you know the definition of transmission line in PCB? In this passage, we will talk about the topic. If you are going to learn professional knowledge of PCB, please check and read the content we prepare below.If you want to order PCB product, please check and custom your order online. What is the brief introduction of transmission line in PCB？ A PCB transmission line is a type of interconnection used for moving signals from their transmitters to their receivers on a printed circuit board. A PCB transmission line is composed of two conductors: a signal trace and a return path which is usually a ground plane. The volume between the two conductors is made up of the PCB dielectric material. The alternating current that runs on a transmission line usually has a high enough frequency to manifest its wave propagation nature. The key aspect of the wave propagation of the electrical signals over a transmission line is that the line has impedance at every point along its length and if the line geometry is the same along the length, the line impedance is uniform. We call such a line a controlled impedance line. Non-uniform impedance causes signal reflections and distortion. It means that at high frequencies, transmission lines need to have a controlled impedance to predict the behavior of the signals. Read our post: why controlled impedance really matters? What are the types of transmission line in PCB？ There are usually two basic types of signal transmission line interconnects used in PCBs: microstrip and stripline. There is a third type – coplanar without a reference plane but it is not very common in use. A microstrip transmission line is composed of a single uniform trace – for the signal – located on the outer layer of a PCB board, and parallel to a conducting ground plane, which provides the return path for the signal. The trace and the ground plane are separated by a certain height of PCB dielectric. A stripline is composed of a uniform trace – for the signal – located on the inner layer of a PCB. The trace is separated on each side by a parallel PCB dielectric layer and then a conducting plane. In addition to conventional microstrip and stripline described above, a coplanar waveguide structure has the signal trace and the return path conductor on the same layer of the PCB. The signal trace is at the center and is surrounded by the two adjacent outer ground planes; it is called “coplanar” because these three flat structures are on the same plane. The PCB dielectric is located underneath. Both microstrip and stripline may have a coplanar structure. When is an interconnection to be treated as a transmission line? Line inductance – The current flow in the transmission line induces the magnetic flux.When the current in the transmission line changes, the magnetic flux also varies due to which emf induces in the circuit. The magnitude of inducing emf depends on the rate of change of flux. Emf produces in the transmission line resist the flow of current in the conductor, and this parameter is known as the inductance of the line.Line capacitance – In the transmission lines, air acts as a dielectric medium. This dielectric medium constitutes the capacitor between the conductors, which store the electrical energy, or increase the capacitance of the line. The capacitance of the conductor is defined as the present of charge per unit of potential difference.Capacitance is negligible in short transmission lines whereas in long transmission; it is the most important parameter. It affects the efficiency, voltage regulation, power factor and stability of the system.Shunt conductance – Air act as a dielectric medium between the conductors. When the alternating voltage applies in a conductor, some current flow in the dielectric medium because of dielectric imperfections. Such current is called leakage current. Leakage current depends on the atmospheric condition and pollution like moisture and surface deposits. When the signal frequencies (in case of analog signals) or the data transfer rates (in case of digital signals) are low (less than 50 MHz or 20 Mbps), the time it will take for a signal to travel from its source to its destination on a multilayer PCB would be very small (< 10%) compared to the time period of one-fourth of a wavelength or the fastest rise time of a digital pulse signal. In this case, it is possible to approximate interconnect by assuming that the signal at the destination follows the signal at its source at the same time. In such a low-speed scenario, the PCB signal can be analyzed by conventional network analysis techniques and we can ignore any signal propagation time or transmission line reflections, etc. How to analyze a PCB transmission line? Basically, high-speed or high-frequency signals generate electromagnetic fields around them during their travel along a transmission line, and their behavior is best analyzed using Maxwell’s electromagnetic equations and the theory of electromagnetic wave propagation. In this method, we have to deal with electric and magnetic fields instead of the usual voltages and currents. The voltage between the signal line and its return path will generate an electric field and a current in the conductors, which in turn will create a magnetic field around them. Thus, voltage, current, and electric and magnetic fields all travel as waves along the transmission line.Wanna know PCB knowledge? Check and read for more.
PCB Glossary ⋅ 08/14/2021 09:31
Crosstalk is the disturbance caused by energy coupling from one PCB trace to another even if they are not in contact. It happens due to the interaction of electric (capacitive coupling) and magnetic fields (inductive coupling). The magnetic field generates mutual inductance, and the electric field generates mutual capacitance between the traces in the vicinity. Mutual inductance is responsible for inducing current on the adjacent (victim) line, which is opposite of the current in the aggressor line. And the capacitor formed due to mutual capacitance will pass the current in both directions on the victim line. In this passage, we will focus on the topic and if you want to learn more professional information check and read the content below.If you want to order PCB product, please check and custom your order online. What are the types of crosstalk in PCB？ Based on trace routing and location of the disturbance on the aggressor and victim lines, crosstalk can be classified as: 1. Capacitive crosstalk: It arises due to the traces that run on top or near to each other, producing a capacitive effect. 2. Inductive crosstalk: It generates due to magnetic field interaction between traces running parallelly over a long distance. Inductive crosstalk is of two types: forward and backward. Forward is the noise/disturbance observed at the farthest end from the driver on the driven line, while backward crosstalk is the disturbance observed at the nearest end on the victim line. Near-end crosstalk (NEXT): It is measured at the transmitter end of the transmission line or a cable. Far-end crosstalk (FEXT): It is measured at the receiver end of the transmission line or a cable. NEXT and FEXT are measured with respect to the port to which the stimulus is applied. It can occur anywhere along a line, whether it is a dual conductor or single-ended. Note: The NEXT value is expressed in decibels (dB) and varies with the frequency of transmission. A higher dB of NEXT means less interference. 3. Power sum near-end crosstalk (PSNEXT): It is the sum of the NEXT of three aggressor pairs as it impacts the fourth victim pair. PSNEXT gives total crosstalks from all the adjacent pairs and involves measuring all pair-to-pair groupings relative to power. 4. Equal level far-end crosstalk (ELFEXT): It is the measurement of the FEXT that involves attenuation compensation. 5. Alien crosstalk: It gives the measurement of crosstalk in PCBs for telecom systems. Above mentioned types are the ways of measuring or quantifying crosstalk in a system. Crosstalk can also be measured using a TDR. For more details, read our post on how TDR impedance measurements work. How to measure crosstalk? Crosstalk is generally specified as a percentage of the signal that appears on the victim line, relative to the aggressor line. It can also be expressed in terms of dB below the driven line level. NEXT varies with the frequency of the transmission since higher frequencies create more interference. The higher the dB value, the less crosstalk is received by the disturbed link/channel. FEXT is calculated from the crosstalk elements of the system S-parameters. The formula for crosstalk is given by: Where: K = A constant whose value always remains less than 1 and depends upon the rise time of the circuit and the length of the traces experiencing crosstalk. H2 = It is the product of the height of the parallel traces. D2 = It is the product of the direct distance between the centerline of the traces. The above equation clearly shows that crosstalk can be minimized by reducing H and maximizing D. Crosstalk in dB is given by: Where, V victim is the voltage on the victim line and Vaggressor is the voltage on the aggressor line. Factors affecting the magnitude of crosstalk1. Degree of coupling between aggressor and victim lines2. The distance up to which coupling occurs3. Effectiveness of the type of termination used What are the causes of crosstalk? · Capacitive and inductive coupling: Capacitive coupling is due to parasitic capacitance and inductive coupling occurs due to mutual inductance.· Difference in propagation velocity: It can be avoided by trace length matching and propagation delay matching.· PCB vias: PCB vias with stubs create reflections, thus ringing which generates crosstalk. One way to avoid this is to back drill the vias.· Increased data rates: With increased data rate, the rise time increases as well. According to Faraday’s law, with an increase in rise time, the crosstalk will also increase. One way to reduce crosstalk between such signals is to increase the spacing between the traces.· Board size: As the PCB board size increases, the trace lengths also increase, and these traces behave as antennas. So, it is important to keep the trace lengths as minimum as possible.Wanna know PCB knowledge? Check and read for more.
PCB Glossary ⋅ 08/14/2021 09:25
Pad in PCB Design
A pad is the exposed region of metal on a circuit board that the component lead is soldered to. Multiple pads in conjunction are used to generate the component footprint or land pattern on the PCB. The two types of pads available are through-hole and surface mount pads. In this passage, we will focus on the topic, please check and read the content below to learn more knowledge.If you want to order PCB product, please check and custom your order online. What are the types of pad? Surface mount pads Pads used to mount surface mount components are called surface mount pads. These pads have the following features: 1. Pad which shows the copper area. This can be rectangle, round, square, or oblong.2. Solder mask layer3. Solder paste4. Pad number (number of pads present for the component) SMD pad vs NSMD pad Proper pad design is critical to ensure the manufacturability of BGA components. There are basically two types of BGA pads – the solder mask-defined pad (SMD) and the non-solder mask-defined pad (NSMD). Solder mask defined (SMD) BGA pads SMD pads are defined by the solder mask apertures applied to the BGA pads. These pads have the solder mask aperture such that the mask opening is smaller than the diameter of the pad they cover. This is done to shrink the copper pad size that the part will be soldered to. The image shows how the solder mask has been specified to cover a part of the copper pad underneath. This can lead to two advantages – firstly, the overlapping mask helps prevent the pads from lifting off the board because of mechanical or thermal stress. The second advantage is that the opening in the mask will create a channel for every ball on the BGA to align with while the part moves through the soldering process. The copper layer of an SMD BGA pad conventionally has a diameter equal to the pad on the BGA. To generate the SMD overlay, a reduction of 20% is traditionally used. Non-solder mask defined BGA pads (NSMD) NSMD pads vary from SMD pads in that the solder mask is defined to not contact the copper pad. The mask is instead created such that a gap is generated between the pad edge and the solder mask. Here the copper pad size is defined by the copper pad diameter instead of the mask layer. NSMD pads can be smaller than the diameter of the solder ball, and this reduction in pad size is 20% of the ball diameter. This approach leaves more room between adjacent pads enabling easier trace routing and is used for high density and fine pitch BGA chips. One disadvantage of NSMD pads is their high susceptibility to delamination due to thermal and mechanical stresses. However, NSMD pad delamination can be prevented when standard manufacturing and handling practices are followed. Through-hole pads Pads used to mount through-hole components are called through-hole pads and are of two types: The plated through-hole (PTH) PTH refers to a pad with a through-hole. The hole wall will be plated with copper and sometimes with solder or another protective plating. The hole plating is done using the process of electrolysis. The plating provides for electrical connection between the different layers of the board. The non-plated through-hole NPTH refers to a pad without plating in the hole. This pad is mostly used for single-sided boards or these holes are used for mounting the PCB in an enclosure and screws are mounted through these holes. Conventionally, unplated holes will have an area around the hole that is clear of any copper (similar to board edge clearance). This is done to prevent shorts between copper layers and parts that are to be placed. What are the considerations of Pad in PCB Design? Ensuring a PCB pad stack design meets manufacturability and reliability requirements needs one to consider several factors: · Maximum tolerances build up the minimum insulation between opposing conductors, which in this case refers to the hole plating and the copper in the trace and plane layers. They need to comply with the standards of the engineered product. For telecommunication equipment, a minimum insulation spacing of 4 mils is required and for other products it is 5 mils.· There need to be robust connections between traces and plated through-holes or vias.· The aspect ratio needs to be such that the hole wall should withstand the stress of the plating process without failure. Even if you follow the guidelines above, drilled holes might not always pass through the board as specified. This might happen due to the following factors: · Drill wander can occur where the drill can deviate from the preferred drilling axis (eccentricity)· Alignment errors in the film layers· Laminate shrinkage during lamination. This might lead to an error in locating the drill hole.· Inaccurate registration of the layers during lamination Drill wander is when drilled holes are off from where they are actually supposed to be. Each manufacturer would have reached a tolerance after going through its process, called drill tolerance. This drill tolerance is used to define the hole shadow of every drill hole. High precision manufacturers can keep the tolerance down to ±5 mils also known as TIR (total included radius). In the US, middle-tier manufacturers can keep this tolerance down to ±6 mils and other manufacturers can hold it down to ±7 mils. It is important for the PCB designer to know where the board will be manufactured to provide accurate allowances for the drill wander error. When it comes to high-volume production, drill wander tolerance should be much higher.Wanna know PCB knowledge? Check and read for more.
PCB Glossary ⋅ 08/12/2021 17:19
Teardrops in PCB layout
Teardrops are a simple addition to a trace that makes a connection to a landing pad. An example is shown below, where I2C lines are connected to vias in a PCB layout. In the image below, the PCB teardrop is some extra copper that fillets out from the trace to the edge of the via's annular ring. By adding this extra copper, the trace has a stronger connection to the annular ring on the via. The format shown below is probably the most common style of PCB teardrop used on vias. The other teardrop style is sometimes called the snowman style as it adds a small circular section at the trace-to-via connection, rather than using a filleted copper section. In this passage, we are going to provide detailed information of teardrops in PCB. Please check our content below for more professional knowledge.If you want to order PCB product, please check and custom your order online. Why to use PCB teardrops? During the PCB fabrication processes, are two potential problems that can occur when drilling a typical PCB: 1. The drill bit may wander during fabrication as there is some very slight inaccuracy and hysteresis in CNC translation stages. As such, the hole and drill can get slightly misaligned, and the drill hole may not line up perfectly with the pad location.2. Layers can shift very slightly during lamination, which results in misalignment of pads on different layers. The drill can hit perfectly on one layer, but it may be misaligned on another layer. PCB teardrops are your insurance policy against drill wander and layer misalignment during fabrication. If misalignment is severe, there is still a high chance the drill hit will not sever the connection between the pad and via. The extra copper will still provide a connection that can be plated. The other reason teardrops are used in a PCB layout is to provide extra strength so that the vias can withstand thermal and mechanical stress. By placing a fillet, we don't have stress concentration at the connection between a thin trace and the pad or via ring. Instead, force on the trace-pad interface will be spread over a larger area, which reduces mechanical stress. Mechanical and thermal stress can arise in a PCB layout during fabrication and during actual operation. In cases with extreme thermal cycling or mechanical shock, a weak interface between a trace and pad can separate or even fracture. This can occur in both rigid and flexible designs. If this happens during fabrication or assembly, a board will have to be scrapped. Where to add teardrops in PCB? · Add teardrops for thru-holes where the trace to pad ratio is small.· Add teardrops for high density boards where the annular ring around vias should be kept.· Add teardrops on flex boards to reduce the stress where the trace joins the pad.· Add teardrops under BGA where have lots of vias.· Add teardrops when traces exist the pad whether it is a solid pad or a pad with a via.· Add teardrops when the trace become narrow.· No need to add teardrops when conductor more than 20mil. How to add teardrops in PCB? · It is always better, and recommends to ask the PCB layout engineer to do the teardrops.· This way you get the same result with any PCB manufacturer how will product your PCB board.· In some cases, this feature is simply a check box on your CAD system or something that your PCB designer will do for you -you just have to ask.· In RF or high frequency boards, it is important to have full control of your PCB layout. Teardrops should be added at the design stage itself.· The PCB fabricator has teardrop creation engine. When auto teardrop creation is allowed to the PCB manufacturer, teardrops connections can be made so DFM routes will be kept.· In any case we recommend you design with tear drops or give acceptance to PCB manufacturer to add tear drops in working Gerber making stage.· In some cases, a teardrop cannot be added, most PCB layout software “know” when to add and when it not possible to add teardrop, not need worry about that. What is the relationship of PCB teardrops and IPC standard? The IPC standards for reliability are divided into Class 1-3. Designs adhering to Class 3 are intended to have highest possible reliability, with applications areas including military electronics and life support equipment. Devices classified as Class 3 need to have minimum possible downtime and longest possible lifetime. Class 3 products also have exacting fabrication and assembly standards that are intended to ensure reliability. Various IPC standards call out specific and generic requirements for Class 3 products. Among the various design and fabrication standards, IPC 6012 and IPC 2221A specify requirements on annular rings, blind/buried vias, and component overhang, solder joints, and much more. Although IPC standards do not place specific design requirements on teardrops, they are mentioned in IPC 2221A as a recommended method to ensure reliability. In Class 3 designs, it's highly recommended to use teardrops on annular rings for all vias.Wanna know PCB knowledge? Check and read for more.
PCB Glossary ⋅ 08/11/2021 17:19
Electronic components used in PCB
Over the last few decades’ electronics technologies and product development have been growing and rapidly have become more and more complex. Knowledge of electronic components is essential to build successful electronic products. In this passage, we are going to provide all the knowledge about electronic components in PCB. Check and read the content below.If you want to order PCB product, please check and custom your order online. What is the introduction of electronic components in PCB? While Electronic components process information in form of electrical signals, a Printed Circuit Board PCB is the skeletal structure on which the electronic components are mounted and soldered to hold them together and provide pathways for information to flow between components through PCB traces. Some of the most commonly used electronic components are resistors, capacitors, inductors, diodes, LEDs, transistors, Crystals & Oscillators, Electromechanical components like relays & Switches, ICs, and connectors. These components have leads/terminals and are available in specific standardized packages that the designer can choose to suit his application. SMT (Surface Mount Technology) and Through-hole are the two types of mounting techniques used to place components on a PCB. What are the common components in PCB? Resistors – Control Energy Resistors are the foundations of current control—which is why they’re so often used in PCBs. These two-ended electrical pieces are fairly simple to understand and integrate into different projects. Resistance is often defined as the “ease” with which objects allow electricity to flow through them. Think of the difference between insulators and conductors; the former obviously possesses higher resistance than the latter. Resistors, on the other hand, allow users to precisely define an object’s level of resistance. They are designed to resist the flow of an electric current by converting the electrical energy into heat—heat that is then dissipated. Resistors can be made of a wide range of materials and come in many different styles. The most common (and highly recommended for beginners) would be resistors made of carbon film in the axial style. Axial style resistors have leads on both ends of the rod. Their body is marked with different colored rings that represent the resistor’s resistance value. Capacitors – Store Energy Outnumbered only by resistors, capacitors are electronic components you’ll definitely find on every PCB board. Whereas resistors control an electric charge, capacitors temporarily store it. Think of them as tiny batteries with even tinier storage space. They are capable of losing and gaining full charge in a split second. Because of this, capacitors are commonly used for “filtering:” a process where a backup source of energy takes over when the main source of power drops in order to not lose or reset data. In PCBs, capacitors electrostatically store energy to later release it to wherever power is needed in the circuit. It works by collecting opposing charges (positive and negative) on two conductive plates (typically metal) with some form of insulating material between them. There are different types of capacitors, often categorized by the conductive material of the plates or the insulating material that separates them. Most beginners and casual hobbyists use polyester capacitors, ceramic capacitors, or radial capacitors. You’ll notice that some capacitors resemble resistors. The most telling difference is that resistors have leads on opposite ends. Capacitors have two leads protruding from the same side. Transformers – Transfer Energy General transformers transfer power from one source to another through a process called “induction.” PCB transformers function the same way. They transfer electrical energy from different circuits—and convert them—by increasing or decreasing the voltage. As with resistors, they technically regulate current. The biggest difference is that they provide more electrical isolation than controlled resistance by “transforming” the voltage. PCB transformers consist of two or more separate inductive circuits (called windings) and a soft iron core. The primary winding is for the source circuit—or where the energy will come from—and the secondary winding is for the receiving circuit—where the energy is going to. Transformers break down large amounts of voltage into smaller, more manageable currents so as not to overload or overwork the equipment. Transistors – Amplify Energy Resistors may be fundamental to current control but transistors are fundamental to all modern electronics. They can, in fact, be considered the building blocks. Contrary to storing, regulating, or controlling charges on the PCB, transistors amplify them. A bipolar transistor, which is the most common type of transistor, has three areas and three pins in which the current flows and is amplified. There are two types of bipolar transistors; NPN and PNP. Both are composed of the (1) base, (2) collector, and (3) emitter, and have both P-type areas and N-type areas. NPN transistors are more commonly used than PNP transistors for a number of reasons. However, both have their advantages and disadvantages depending on the project. Diodes – Redirect Energy Going back to our PCB board – city comparison, diodes are basically the one-way streets on a printed circuit board. These two-terminal components control and redirect energy flow by allowing the current to flow down one direction and blocking it from moving down the other. The flow is typically from the positive terminal (called the anode) to the negative terminal (called the cathode). Like resistors, diodes use electrical resistance to control the flow of energy. High resistance in one direction and zero resistance in the other effectively blocks the current from flowing in the wrong direction and potentially damaging the equipment. The most common diode that many people—even non-hobbyists—are familiar with is light-emitting diodes or LEDs. Other common examples of PCB diodes include Zener, high-speed switching diodes, and Schottky diodes. Battery – Provide Energy In theory, everyone knows what a battery is. Perhaps the most widely-purchased component on this list, batteries are used by more than just electronic engineers and hobbyists. People use this little device to power their everyday objects; remotes, flashlights, toys, chargers, and more. On a PCB, a battery basically stores chemical energy and converts it into usable electronic energy to power the different circuits present on the board. They use an external circuit to allow electrons to flow from one electrode to the other. This forms a functional (but limited) electric current. The current is limited by the conversion process of chemical energy to electrical energy. For some batteries, this process could finish in a matter of days. Others might take months or years before the chemical energy is completely spent. This is why some batteries (like the batteries in remotes or controllers) need to be changed every few months whereas others (like wrist watch batteries) take years before they’re all used up. There are different types of batteries available for PCBs, but we would definitely recommend getting rechargeable ones. Integrated Circuits – Multi-Function Powerhouses Integrated circuits are the powerhouses of all PCBs. Batteries might be the source of energy, but circuits are the power factories. These tiny wafers house thousands (or even millions) of transistors, resistors, and capacitors. Because of that, they can amplify, oscillate, and process energy in a printed circuit board—just to name a few functions. As the name suggests, integrated circuits (or ICs) are basically circuits that have been integrated into a PCB board through minimization. These wafer-like components are usually made of silicone and encased in a plastic housing. The more modern ones can also use digital or analog technology to perform calculations. These types of technology further define the two types of ICs: digital and analog. The best one for beginners depends on the kind of project to be carried out. Digital Integrated Circuits are typically used in computers and consumer electronics. Analog Integrated Circuits (also called Linear) are typically used in audio and radio frequency amplification.Wanna know PCB knowledge? Check and read for more.
PCB Glossary ⋅ 08/11/2021 17:02
ENIG VS ENEPIG
During the manufacturing of PCB, the surface finishing is very important to the finished productions. In this passage, we will focus on the ENIG and ENEPIG. If you are going to learn the difference of them, please check the content we provide for more information.If you want to order PCB product, please check and custom your order online. What is the importance of telling ENIG and ENEPIG? Copper layer on PCB tends to be oxidized in the air so that copper oxidation tends to be generated, which will seriously lower soldering quality. Surface finish, however, is capable of stopping copper pad from oxidizing so that excellent solderability and corresponding electrical performance can be guaranteed. The uprising market demands on miniaturization, higher functionality and reliability for electronic devices push PCBs towards thinness, light weight, high density and higher speed of signal transmission. Accordingly, surface finishes have to embrace upcoming challenges in terms of stability and reliability to be compatible with development requirement mentioned above. Moreover, based on rising consciousness of environment-friendly sustainable development, environmental pollution issues concerning PCB surface finishes are attracting increasingly more attention from the globe. The implementation of legislations of RoHS (Restriction of Hazardous Substances) and WEEE (Waste Electrical and Electronic Equipment) laid by EU aims to eliminate the hazardous substances such as lead and mercury from electronic products, calling for green or lead-free manufacturing of PCB surface finish. Nevertheless, it's a little difficult for people to tell differences between ENIG and ENEPIG, let alone to be aware when to depend on which. The following content in this article will provide definitions of ENIG and ENEPIG and their manufacturing processes, discuss advantages and disadvantages of them and aim to supply a guide on when to use each finish in specific situations. What is advent of ENIG and ENEPIG? As early as 1990s, due to PCB development towards finer lines and micro vias plus protruding disadvantages of HASL and OSP, like flatness issues of the former and flux elimination issues of the latter, ENIG started to be used as another alternative for surface finish in multilayer PCB fabrication. In order to defeat black nickel board, the leading weakness of ENIG, ENEPIG comes out as an upgrading version of ENIG. With plating palladium added between electroless nickel and immersion gold, ENEPIG results in containing a thin layer for resistance whose thickness usually falls in the range from 0.05μm to 0.1μm. Palladium layer plays a role in stopping immersion gold technology from corroding nickel layer. As a result, ENEPIG is capable of defeating the defect of black pad held by ENIG. Furthermore, ENEPIG features highly-reliable wire bonding capability, excellent multiple reflow soldering capability and contains switch contact surface, which makes it able to meet stringent requirement of PCBs with high density and multiple surface packages simultaneously. Based on those advantages, ENEPIG is also called universal finish. What are the advantages and disadvantages of ENIG and ENEPIG? In the 1990s, with the development trend of PCB fine lines and micro-via and flatness problems of HASL (hot air solder leveling) and solder elimination problem of OSP (organic solderability preservatives), ENIG technology began to be massively used in PCB fabrication. Compared with ENIG, ENEPIG technology was applied in PCB fabrication as early as 1980s. However, ENEPIG wasn't been massively used and popularized as a result of its high cost and products' low requirement in terms of surface finish. At present, the requirements of miniaturization, thinness and multiple functions give more opportunities to ENEPIG. ENEPIG technology develops based on ENIG technology with palladium layer added so that its performance has been highly improved. The reasons are: a. Palladium layer with dense membrane structure totally covers on nickel layer and phosphorus content in palladium layer is less than ordinary content in nickel layer so that the generation conditions of black nickel is avoided and black pad possibility vanishes.b. The fusion point of palladium is at 1,554°C that is higher than the fusion point of gold (1,063°C). Therefore, the fusion speed of palladium at a high temperature is relatively slow with sufficient time for the generation of resistance layer to protect nickel layer.c. Palladium has higher hardness than gold, which results in the improvement of solder reliability, wire bonding capacity and antifriction.d. Tin-Palladium alloy has the strongest anticorrosion capacity that is capable of stopping the creep corrosion caused by primary cell corrosion so that lifespan can be increased.e. The usage of palladium is capable of reducing the thickness of gold layer, which downsizes the cost by 60% compared with ENIG. What is the application comparison of ENIG and ENEPIG? ENIG and ENEPIG application fields are different based on their distinctive advantages. ENIG is suitable for lead-free soldering, SMT (surface mounted technology), BGA (ball grid array) package etc. The industries and products ENIG is capable of serving include data/telecom, high end consumer, aerospace, military and high performance devices and medical industries. Furthermore, ENIG is especially used in flex market owing to its high reliability. ENEPIG is capable of meeting more stringent requirements of multiple types of packages including THT (through-hole technology), SMT, BGA, wire bonding, press fit etc. What's better, ENEPIG is also suitable for PCBs with different packaging technologies. As a result, application fields ENEPIG can serve include aerospace, military and high performance devices and medical industries with higher requirement of density and reliability. Actually, it's PCB board manufacturers' job to provide top-quality products to their customers. As a significant step during PCB manufacturing, high quality of surface finish definitely decides high quality of circuit boards. Therefore, PCB manufacturers have to ensure that surface finish is capable of meeting requirement called by circuit boards and end products they'll serve.Wanna know PCB knowledge? Check and read for more.
PCB Glossary ⋅ 08/10/2021 17:11
Today, no new car can run without an onboard computer — and those computers need sophisticated automotive printed circuit boards to make them run. In this passage, we are talking about the automotive PCB and the application. Please check and read the content we prepare below for more information.If you want to order PCB product, please check and custom your order online. What is the basic introduction of automotive PCB？ Furthermore, it is estimated that automotive electronic system with a market capitalization of 191 billion dollars will rocket to that with 314.4 billion dollars by 2020, with an average compound growth rate of 7.3%. A top-level automotive possibly contains 150 electronic control units that are mostly sensors and processors inside cockpit. According to some report, real value of 65% of electronic products lies in dynamical system, automotive body and chassis and most is concerned with digital power. Electronic value in electromotives will go over 70%. Automotive containing electronic equipment are sure to apply electrical circuit board. In 2014, global automotive PCBs account for 4.6 billion dollars and this number is estimated to be over 7 billion dollars by 2020. Application of automotive system is to increase automotive performance that up to now is displayed in three aspects: a. Environmental improvement refers to fuel saving and exhaust reduction, that is, a process from gasoline, natural gas and biofuel to hybrid power and pure electricity. Electromobiles have become the main development trend. b. Security increase refers to traffic accidents reduction, ranging from airbag to radar monitoring, stereo camera, night infrared monitoring, automatic collision-avoidance and automatic driving. It's estimated that self-driving automobiles will be commercialized in three years. c. Convenience and comfort ranges from audio specific to automobiles, video and air conditioner to computer, mobile communication, Internet, navigation and electronic toll collection all of which have to be more convenient and user-friendly. What is the basic requirement of automotive PCB？ • Quality insurance requirement Automotive PCB manufacturers should conform to regulations of ISO9001. We are fully compliant with the ISO9001:2008 quality management system and is committed to adhering to the strictest standards in manufacture and assembly. Automotive products have their own particularities. In 1994, Ford, GM and Chrysler combined to set quality control system in automotive industry, QS9000. In the early 21st century, compatible with ISO9001 standards, a new quality control system in automotive industry was published, that is, ISO/TS16949. ISO/TS16949 is a set of technological regulations in global automotive industry. Based on ISO9001, with special demands in automotive industry added, it focuses more on defect prevention, decreasing quality fluctuation and waste that tend to be generated in automotive component supply chain. When implementing ISO/TS16949, special attention has to be paid to primary 5 key tools: PPAP (Production Part Approval Process) regulating that products should receive customers' approval prior to volume production or after modification, APQP (Advanced Product Quality Planning) regulating that quality plan and previous quality analysis should exist before production, FMEA (Failure Mode and Effects Analysis) analyzing and coming up with measures to prevent products' potential failure, MSA (Measurement System Analysis) necessarily analyzing variation of measurement result to confirm measurement reliability, SPC (Statistical Process Control) mastering production procedure and product quality change with the application of statistical techniques. Therefore, the first step for PCB manufacturers to enter automotive electronic market lies in getting TS16949 certificate. • Basic requirement of performance a. High reliability Automotive reliability primarily comes in two aspects: lifespan and environmental resistance. The former refers to the fact that normal running can be guaranteed within a lifespan while the latter refers to the fact that PCB functions remain unchanged when environment changed. The average automobile lifespan in 1990s is in the range from 8-10 years and the present range from 10-12 years, which means that both automotive electronic system and PCB should fall within this range. In the process of application, automobiles should withstand climate change, from extremely cold winter to hot summer, from sunlight to rain, and environment change owing to temperature rising as a result of their own running. Put it differently, automotive electronic system and PCB have to withstand multiple environmental challenges including temperature, humidity, rain, sour fog, vibration, electromagnetic interference and current surge. Additionally, since PCBs are assembled inside automobile, it is mainly influenced by temperature and humidity. b. Light weight and miniature Light weight and miniature of automobiles is beneficial to energy saving. Light weight derives from weight reduction of each component. For example, some metal parts are replaced by engineering plastic parts. Moreover, both automotive electronic equipment and PCB should be miniature. For example, the volume of ECU (Electronic Control Unit) applied in automobiles was approximately 1200cm3 at the beginning of 2000 while that is less than 300cm3, decreasing by four times. Plus, starting point firearm has transformed from mechanical firearm connected by wires to electronic firearm connected through flexible wires and with PCB inside, decreasing by more than 10 times in terms of volume and weight.Wanna know PCB knowledge? Check and read for more.
PCB Glossary ⋅ 08/07/2021 17:23
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