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Using solder paste in rework

Joe Cameron

#11741

Using solder paste in rework | 25 April, 1999

Hello all,

Been doing some comparisons on joints made using the soldering iron versus reflowed solder paste (on a QFP package). The difference is quite significant: the joints made by the soldering iron are inconsistent and in many cases not filled at the heel at all, raising MANY reliability doubts on our reworked products. We are conducting some tests on the effects of the thermal shock from applying sudden heat on a ceramic chip. Tell you more on that later, but we are convinced that reflowing at the solder bench would be a better choice at least for the QFP.

My question is, how many companies are there making hot-air pencils specific for reflowing solder paste at the rework bench? Our hot-air guns won't do because of the large air flow blowing the solder every which way.

Thanks, Joe

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Earl Moon

#11742

Re: Using solder paste in rework | 25 April, 1999

| Hello all, | | Been doing some comparisons on joints made using the soldering iron versus reflowed solder paste (on a QFP package). The difference is quite significant: the joints made by the soldering iron are inconsistent and in many cases not filled at the heel at all, raising MANY reliability doubts on our reworked products. We are conducting some tests on the effects of the thermal shock from applying sudden heat on a ceramic chip. Tell you more on that later, but we are convinced that reflowing at the solder bench would be a better choice at least for the QFP. | | My question is, how many companies are there making hot-air pencils specific for reflowing solder paste at the rework bench? Our hot-air guns won't do because of the large air flow blowing the solder every which way. | | Thanks, | Joe | The hot air gun we use is a programmable rework machine. I know this doesn't answer you needs, but we find next to no defects using this type device.

We remove, place, and reflow QFQ's, BGA's, and uBGA's with the system using paste, or not (depending on the application - when not we use paste flux instead of liquid for better compliance). The biggest issue with pasting often is the near excessive voiding encountered with all device types. However, we've run considerable testing (HAST/HALT) and found no long term reliability problems.

Again, I know this does not answer your needs. I do believe there to be a cheaper system than ours that will satisfy your needs. Big Steve found one that seems fairly reasonable for less damandig boards than ours.

Earl Moon

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#11743

Re: Using solder paste in rework | 25 April, 1999

| Again, I know this does not answer your needs. I do believe there to be a cheaper system than ours that will satisfy your needs. Big Steve found one that seems fairly reasonable for less damandig boards than ours. | | Earl Moon

Hi Joe!

Yeah Earl's right, if you wanna know how to do things onna shoestring, just ask me...I've been doing without for so long I won't know how to act if I get some decent money to buy what I want.

I use a Hakko 850...real fancy machine huh? It lists in Com-Kyl's catalog for a whopping $1140...it does a okay job...but very operator dependant. I try and give the basic settings for our operators for specific parts, but it just depends on the laminate thickness, how much metal there is in the board, how close they hold it to the part, etc., etc...

It has two controls on it, a heat control, and a airflow control. So you can dial that thing down airflow wise so that blowing off the solder paste won't be a problem at all.

There's all kinds of nozzles that you can get for it including a little pencil tip one...I don't quite remember what the prices of the nozzles were, but I think they run around $50.00 - $150.00 each. But rather than use the pencil tipped nozzle, get the one for the size QFP you're doing...that would be my recommendation. Do it all at once instead of heating a small area of the QFP at a time...I wouldn't think that would be too good for the QFP.

Like I said, this is a very operator dependant unit, but in the right hands you can do quite a bit. Even I can use it halfway decent...and that's saying something! hehehe...

-Steve Gregory-

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