Welding is a lot like soldering components on a circuit board in that there are tell-tale signs that indicate a good solder joint. The importance of having good solder joints to PCB quality control is well-known, as bad joints can lead to unreliable signal transfer or tombstoning and no signal flow at all.  

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In this article, we will provide you everything about the details about PCB solder joint inspection. If you are interested in the importance of it please check and read the content below for more information.

What are the common failures of solder joint?

This failure is more prominent in Land Grid Array (LGA) and Quad Flat No Lead (QFN) packages, as they often do not have solderable side terminations or the component manufacturing process has made them poorly solderable. Often, a lack of protective coating of tin on the surface of copper lead frame is the cause of poor solderability of the edge termination. Although IPC 610 does not require side terminations to be solderable, customers prefer to see a joint. Additionally, the presence of solder on the edge termination helps Automatic Optical Inspection.

·  Open joints

·  Incomplete solder coverage

·  Solderability failure

·  Floating LGA

·  Component Damage

·  Solder skip

·  Solder balls

·  Fillet lifting in through holes

·  Non-Coalescence of paste

·  Tin whiskers

·  Incomplete reflow of pin in hole

·  Insulation contamination

What is perfect solder joint in PCB?

It’s difficult to encompass all types of solder joints into one comprehensive definition. Depending on the type of solder, PCB used, or component connected to the PCB, the ideal solder joints might vary drastically. Still, most of the perfect solder joints have:

·  Complete, solid wetting

·  A smooth and shiny surface

·  A neat concave fillet

To achieve an ideal solder joint, regardless of whether it’s an SMD solder joint or a through-hole solder joint, it’s necessary to use the right amount of solder, an appropriate solder iron tip heated to an accurate temperature, and a prepped PCB contact with a removed oxide layer.

Here are nine of the most common problems and mistakes that can happen on solders, usually when soldered by an inexperienced worker:

Solder Bridges

PCBs and electronic components are becoming smaller and smaller, making it difficult to maneuver around the PCB, especially when trying to solder. If you’re using a solder iron tip that’s too large for the PCB, you might create unwanted solder bridges.

A solder bridge is when soldering material connects two or more PCB connectors. This is quite dangerous and, if undetected, can cause the board to short circuit and burn out. Make sure to always use the right size of soldering iron tip to prevent solder bridges.

What is the importance of PCB solder joint inspection?

It’s important to check with your PCB assembly supplier to understand the technology involved in their soldering process and in solder joint inspection. If your supplier doesn’t invest in a sophisticated machine or relies only on manual inspection (a.k.a. bare eyes inspection), you could be in for a rough ride.

When the PCB is not properly inspected, bad solder joints and short connections may go undetected, causing serious problems in the final product. Often, these problems only become evident during QA testing. As you power on the PCB, short joints may result in burning out an IC or two.

You may also spend hours troubleshooting the PCB to find out why components are malfunctioning. Unlike solder joints that are manually created, bad joints from reflow machines can be hard to detect. Even if you’re equipped with a magnifying glass, performing a manual solder joint inspection can be a painstaking effort.