Welcome to our latest Defect of the month – solvedthis month we illustrate secondary reshaping Low temperature soldering. Secondary melting is when part of the solder approaches the melting point temperature or is in a semi-liquid state. One of the reasons I’ve seen this happen with traditional lead-free SAC technology, and I’ve also seen it at low temperatures with lead contamination. In both situations, it is very unusual for this to happen today, but it is better to know about the problem than not to be aware of it and to experience something similar. If part of the joint at one boundary begins to pass into a semi-liquid state, but at a lower temperature its lead, which lowers the temperature at which the material passes from liquid to solid state and vice versa.

The images show the separation of the joint and the surface of the joint, which has separated with a non-brittle tear, this is a secondary overflow or liquid rupture

If you introduce lead contamination in part of the joint from the end or the coating on the substrate surface, the interface will actually return or become semi-liquid at a much lower temperature than the overflow temperature of the base alloy. If we take into account the low-temperature SnBiAg solder around 138Fr.C introduced in the equation, then the actual potential reflux temperature with liquidus temperature is about 100Fr.C with lead. If you then subject the board module to a temperature somewhere near this lower end and it has lead contamination as part of the interface, then the joints can actually separate and we call this a secondary overflow. I said that this is very unusual, it should not happen today, but I illustrate it and show you examples. Our video simulation shows what happens when this happens in production

This is just one of the videos about the defect of the month, previously presented by IPC, SMTA, SMART Group and Circuits Assembly magazine, which helps to better understand the problems of the process and supports the training of younger engineers. We recently celebrated being 100, that’s the number of videos produced, not Bob’s age, Bob!

Company may sponsor our videos and photo defect guides

Here is your opportunity to sponsor our regular Defect of the month videos on materials, soldering, assembly, cleaning and design of printed circuit boards. Produced by Bob Willis over the years, there are many topics that have been covered and are unique to the industry for more information on sponsorship Defect of the month videos for 6 or 12 months, contact claire@wnie.co.uk

Here is a link to a sample video

In addition, we also have our favorites Guides for defects in the photographic process for engineers to download for free after registration. Our first guide was presented Guide to inspection and defects with soldering iron paste

Our next two guides will include:

Low temperature solder inspection and defect guide

Manual for robotic soldering, manual for inspection and defects

0201 and 01005 Manual for overflow and defects of chip components

Bob Willis – Defect of the Month video guide

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