Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


QFP Removal

Jim

#27283

QFP Removal | 16 February, 2004

I have about 200 PCB's from which a 20mil pitch QFP must be removed, cleaned and re-used (will place them back in trays for the P&P machine to place the parts on new boards). My intitial concern is: how can we remove the parts in an efficient manner? As far as the equipment, the only solution that I see is using a forced air rework station however, this will involve removing one part at a time. Since a typical reflow cycle is 3.5 minutes, it will take some time just to remove the 200 QFP's. The goal is to save and re-use the component, the PCB is scrap and will be tossed after I get the component off. I thought of running the boards through the reflow oven and somehow pulling the chip during the cycle however, the "pulling" part of it while it is in the oven is difficult to contemplate. Any suggestions as to a practical method of removing the QFP?

Once the component is removed, how do I clean off the excess solder left on the leads?

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#27288

QFP Removal | 16 February, 2004

Removal: Run the board through the reflow oven with the cooling zone turned off. Then pick the QFP with a pair of tweezers.

Replace: Don't clean the solder from the QFP. Just dip them in tacky flux, place the component, and reflow.

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#27290

QFP Removal | 17 February, 2004

Check out Zephyrtronics, they have a low temp solder system that we use with very good results. http://www.zeph.com/lowmelt.htm

Good Luck

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#27291

QFP Removal | 17 February, 2004

Bobvsi: A couple of questions for you: * How does adding a low melting point solder to your "regular" [near eutectic] solder increase the speed of removing components? * How does what are the solder alloys that form when using this low temoerature solder with a "regular" solder?

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RDR

#27292

QFP Removal | 17 February, 2004

Do you have a bake oven that will reach 200C? You could bring a batch of boards up to temp and then start the pluckin'. A sfar as the solder goes if you apply flux to the leads they remove very clean as far as solder goes. To remove the flux we place into the matrix trays and then process through cleaner. we use rubber bands to hold the parts in the trays during cleaning cycle. If you don't have an oven Daves suggestion works well also. Sometimes you need to generate a new profile delpending on your oven to ensure that the PCB is still in reflow when it exits. You may also have to remove any shrouding that may be present on the exit of your oven.

Russ

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#27293

QFP Removal | 17 February, 2004

Hi Dave, 1. As far as speed of removing componants, we use a board preheater to bring board temp to about 150 C. Then add a flux and then flood all 4 sides of the componant with the low temp solder. Using a suction tool the part comes right off. They advertise this as a 180 second process, but that doesnt take into consideration board size, thickness and other considerations. Not sure if there is a faster way out there, but I like that all the other parts on the board aren't reflowed and I also appreaciate keeping the temps lower on the qfp.

2. You would have to contact the company to get specifics on what alloy forms when co-metalization occurs. I can tell you that this alloy has a low temp melting point and that it cleans up rather easily.

Hope this helped somewhat. For the record I dont have any association with this company, I saw a demo at a show and figured I would give it a try, it worked for me.

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#27301

QFP Removal | 17 February, 2004

I might be saying something that will get me laughed off of SMTnet forever, but when faced with a similar problem here's what I did. Since I was removing parts I didn't see why I would be concerned about all the things that go on in a good temperature profile, I just wanted to melt the solder as quickly as possible and get the part off of there. So, I just made a profile for my hot air rework machine that heated the component as quickly as possible without violating the component manufacturers maximum temperature slope recomendations. I still see this profile used from time to time for part removal, and I haven't seen any adverse affects from it yet. I think I would go with the no cool-down oven solution if that's an option for you since you could remove alot of components really fast that way. But my way doesn't interfer with production and only reflows the part you want to remove, so maybe it might work out better for you

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Steven

#27315

QFP Removal | 18 February, 2004

A hot plate should do it. Since your throwing the board away a good hot plate could get you to just above reflow topside and you could remove them all at one time. To do this however the bottom side of the board would probably be damaged, but you don't care.

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Cogiscan Track Trace Control

Reflow Ovens thermal process improvement