Non-wetting on QFP lead

Hi Guys,

I need help. I�ve a trouble with non-wetting problem on the lead of 208 pin, 20 mils pitch QFP. We are on intrusive reflow. I never faced this problem before on this product after running them for about 2 years now.

This occurred on one particular area, and when it�s happened, it�s only happen on one of the lead. The temperature on these leads were initially measured and there are at 206 Deg C � 208 Deg C. I realized that it could be too low as the leads� plating composition falls within 80% +/- 5% Pb, and to make it worse, some of the pad are connected to a big copper/ground plane on the other layers. So I�ve increased the temp. to 210- 214 Deg C max. I cannot go any higher as temperature at the other comp has exceeded 230- 240 Deg C and melted the plastic connectors. After doing this, the failure rates has improved, from 4.2% to 0.48%. I realized almost all solderable material can be soldered at a higher temperature but, my limitation is � I�m running intrusive, and I�ve to take care of the other parts as well. Unless if I add some kind of temporary heatsink to these connectors during reflow. What should I do ? should I change the process ?

I suspect the part has some variance in their plating composition � higher may be, I could be wrong. I�m waiting for the vendor to supply me with the plating composition history.

Here is the details of my setting. I would appreciate if any of you guys can review them and gimme your feedback :

a) Profile - ramp rate 1.4 Deg C/sec , Preheat time at 120/150 = 90 sec, time above 183 Deg C = 65 secs, time to 183 Deg C = 4 minutes, peak = min 211 � max 236 deg C.

b) Located at the centre of the board. There is one QFP with the same lead-frame same vendor, located on one corner, close to the edge � don�t face this problem, and the temperature measure at all it�s leads were around 212 deg � 221 Deg C.

c) Temperature difference when profiles were taken with and without loading were about 5 Deg C. at the one mentioned above were with loading.

d) Oven performance � tip-top, all the temperature changed event has been logged and monitored. No deterioration either on the temperature as well as the conveyor�s speed.

I�m running out of idea, anyone with suggestion on what should I do ? Any idea on how to run DOE on this particular case. How can I prove to the vendor that their part is contributing to this problem.

Desperado, Yngwie

reply »