All, I am having a problem with joints being soft after SMT. Especially 25 mil and smaller parts. It seems as though you can slide the leads right off of the solder. It takes only about 30-40 oz. of compression at 45 deg. to move leads off of joints. With HASL boards, however, I almost rip the pads off before the lead seperates from the solder. I have increased the time of reflow to almost 80s, but the joints have had no substantial increase in strength. We have experimented with more agressive 63/37 solder pastes, and that has helped some, but the joints still appear to be weak. We have also monitored the board house's gold process, and they have ensured us that the gold is w/in 5 micro inches. They also check their nickel bath every 4 hours for phosphrous content. Their nickel bath, however, is electroless. I have heard this may cause problems. We have also requested they decrease the time of gold bath by half, and this has not helped. In any case, we are not experiencing this problem with another PCB supplier. We currently use 5 mil stencils with 50-55% aperture reduction. I have never seen this problem before, but I don't have much experience with gold. Some help here would be greatly appreciated.
Does anyone have any suggestions on what we can do to increase the strength of these joints?
Does anyone have a spec for compression tests on joints?
Is another type of solder paste (other than 63/37) preferable w/gold?
Statement: This post is only the personal view of the author and does not represent the opinions of ALLPCB.com.