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Non wetting on fine pitch product

Views: 2227

#43785

Non wetting on fine pitch product | 7 September, 2006

I have been getting non wets on fine pitch QFP packages on random leads during reflow process. I noticed that every time there is some flux residue left between the non-wet lead and the solder pad. No residue was not observed on the rest of the good leads. Does this indicate that the lead did not see enough heat or could have the solder paste slumped early leaving behind the flux residue trapped between the component lead and solder pad? Can anyone pls explain this phenomenon? Thank u.

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Bubba

#43787

Non wetting on fine pitch product | 7 September, 2006

Check for coplaner leads if this just exists at reflow process, i.e. look at part before oven, turn on 3D at placement machine.

If you see after wave solder, the wave could cause coplanarity issues on top as well if you are going slow enough to reflow the QFP over wave. Increase conveyor speed accordingly, use fixture to stiffen board.

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#43789

Non wetting on fine pitch product | 7 September, 2006

Did check the coplanarity of the failed lead and found it to be as good as the wetting leads.

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Bubba

#43792

Non wetting on fine pitch product | 7 September, 2006

OK, part touching paste before reflow? Check part. Maybe bad plating. Check reflow profile by slowing conveyor.

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#43797

Non wetting on fine pitch product | 7 September, 2006

Is the solder reflowing on the pad but not wicking up the lead, or does there appear to be insufficient solder to wet both, or is it not reflowing at all, or.....?

Have you verified your profile? What is the condition of your paste (expiration date, stirred well, etc.)? What does it look like before entering the reflow oven? Have you looked *closely* (40X) at your boards right before reflow?

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#43798

Non wetting on fine pitch product | 7 September, 2006

Can u elaborate on the bad plating? Have u had any experience on this before? The component has 90/10 Tin lead plating

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#43799

Non wetting on fine pitch product | 7 September, 2006

Yes solder is reflowing on the pad but doesnt wick up the lead. Solder paste is sufficient. It just forms a saddle like appearance beneath the failing lead. The failed lead doesnt get reflowed at all.

What puzzles me is how can hundreds of leads wets well while one single lead doesnt? to make it worse, it's happening on random leads.

The profile has not been changed. How critical is paste stirring to this problem? Have u encountered this type of issue before? If yes, how did u resolve it?

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#43810

Non wetting on fine pitch product | 7 September, 2006

Questions are: * So after you spot one of these leads sitting on a nice pillow of solder, what happens? * Do you rework the part? * Does it take solder? * What do you do to make it take solder, if it does take solder?

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#43818

Non wetting on fine pitch product | 7 September, 2006

Yes the part is reworked. It solders when it's reworked.

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#43822

Non wetting on fine pitch product | 8 September, 2006

That's your clue. Your reflow is running ~240*C and your soldering iron is running ~370*C. Dial-up the heat.

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#43827

Non wetting on fine pitch product | 8 September, 2006

By profile (profile has not been changed) are you referring to the oven zone settings or the actual charted profile of a trip through the oven as recorded by a thermal profiler?

Some ovens will continue to function without warning as long as temps remain within alarm limits, but the amount of heat transfer to the product may take a hit if you lose a blower or heating element. I shrunk the alarm limit window on our Hellers for that reason.

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