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Non-wetting on QFP lead



Non-wetting on QFP lead | 21 November, 2001

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

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Non-wetting on QFP lead | 25 November, 2001


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Non-wetting on QFP lead | 26 November, 2001

Sounds like you are thinking correctly.

I'd guess your fab has gotten "smart" and changed your bare board, as you suggest.

So, you've got two choices: 1 Rework the QFP. 2 Remove the lower temperature PTH components and solder them to the board some other way.

On figuring-out the source of this problem: Have your fab do sections of this board and the previous [good] board and analyze the differences. If he won't do it, find someone that will do it.

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Non-wetting on QFP lead | 26 November, 2001

Hehwoo, bin eatin' turkey up at mums house.

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