AMZ-FX said:
Yes, I know.. I have been soldering longer than many reading this thread have been out of diapers. I got some military spec soldering training back in the '70s when I was working on a navy project at MIT Instrumentation Labs, but had already been soldering for years as a hobbiist. I have been dealing with surface mount for almost as long as it has been around. (At Peavey we put SMT parts on the bottom of SS PCBs years ago.)
I have removed way too many SMT components from one of my current production boards that I do some rework on without once lifting a pad. In fact I had to buy a dremel tool to grind through one trace I needed to open, because I couldn't lift it with heat when I wanted to (yes that's an old PCB rework trick. Cut through the trace in two places with an exacto knife, and lift a whole section out with heat).
With this batch of PCB from GP, I was removing solder with some solder wick, to try again on a quad resistor array that was crooked, and to my surprise the pads came up with the solder. The pads only connected to each other so there was no long PCB trace to wick away heat, so this was a worst case scenario for heat and copper adhesion, but I didn't think I fried it. The evidence suggests otherwise. ???
Perhaps it's a substandard batch of copper clad, I don't know. I do know that these appear to be less robust than every other board I've worked with in recent history. I also notice that the solder mask seems to come off unusually easily too. I can live with ugly, but the traces lifting was a small PIA.
Using a light hand, I have finished loading all the difficult parts to a couple PCB with no more problems.
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I don't like to make uncomplimentary comments about anybody's business casually, that's just irresponsible. So I just went back to another board and did some simple testing. On my design I laid out some extra unused dome switch footprints so I have some narrow traces and large lands I could sacrifice without destroying a usable PCB. I was able to lift a 10 mil trace very easily. i was also able to lift an almost .250" pattern with little effort. Once I lifted the end, I was able to tear off the copper very easily. For comparison I went to an earlier cut PCB I had laying around from a domestic vendor. On the 10 mil trace I was still able to break it but it took more time, heat, and effort. Then I tried to lift a .200 trace. At first I couldn't lift it, so I cut through it with a knife and with a combination of heat and bearing down real hard with the iron I was finally able to lift it. Once I got the end lifted I was able to tear it from the fiberglass but there was noticeably stronger adhesion.
Perhaps a 2:1 difference in adhesion (estimated), so not night and day, and I might still use GP in the future because they are notably cheaper, and will work if used carefully, but I stand by my original impression that the copper adhesion is less than I am accustomed to.
FWIW in normal production the lands and traces will not see anywhere near these kinds of stresses, but since this is a DIY forum, with perhaps less than experienced solderers, I post this warning. If I am the only person who was ever bit by this, good for everybody else.
So don't be afraid to use these, but use the right tools and a light hand for any rework since they are not as robust, in my one rat experience.
JR
PS: On future layouts I might be tempted to add some more copper and perhaps fatter traces around pads like that, to help them dissipate heat, while some of the modern packages use such tight lead pitches there isn't much you can do but use narrow traces. Oops, another learning experience in this ongoing IQ test we call life... trouble is you get the test first and answers later. 8)
