In this final planned post of the “What damage does the assembly process do to a pcb?” series we shall discuss copper diffusion.
What is copper diffusion?
When soldering, copper diffusion is a process in which copper atoms are removed from the copper surface and redistributed into the solder over a wide area.
Back in 2005 I was running some thermal and solderability tests on multilayer boards using various types of cured laminates, different surface finishes and various solder alloys. I was doing my RoHS and Lead-Free due diligence. I had a whole range of tests that I was running. One test consisted of solder dipping a test board in 288°C solder for 20 – 5 second intervals. I was trying to make a multilayer board built on phenolic laminate delaminate. When I reached the tenth dip I had to stop my test. I didn’t make the board delaminate but I did dissolve away much of the copper circuitry into the solder pot. (more…)