[SOLVED] Desoldering the P2 chip from EVAL board
doggiedoc
Posts: 2,239
This may very well be one of those “If you have to ask.....” situations. I short circuited my P2 on my rev B P2-EVAL Board last week and I’ve already got 4 replacement ICs from the original order. My plan was to use those for a new board, but I really need to flesh things out on the EVAL board more. So, I plan to desolder and replace the P2 IC on my P2-EVAL board by hand.
My question is about the ground pad under the chip. I seem to remember Chip having to work at how to get heat to the solder under the chip (by hand). I was planning to use hot air to remove and after cleaning the pads - syringing the new solder paste in place and reflowing it with the chip in place with hot air again. I suspect I shouldn’t reflow the whole board in my IR reflow oven. How would you do it?
Doc
My question is about the ground pad under the chip. I seem to remember Chip having to work at how to get heat to the solder under the chip (by hand). I was planning to use hot air to remove and after cleaning the pads - syringing the new solder paste in place and reflowing it with the chip in place with hot air again. I suspect I shouldn’t reflow the whole board in my IR reflow oven. How would you do it?
Doc
Comments
I'd put the board on a hotplate and bring it up to 150C. Then with a generous squidge of flux around all the pins, and a decent capacity hot air gun probably set to 350C, work the hot air on the top of the chip to remove it.
That's the tough part. After that, a good clean up and remove all the lead-free solder. Put down some fresh leaded solder and flux, or solder paste, and repeat the pre-heat and hot-air gun process to re-appy.
I've done a couple of Eval boards like that, and it goes pretty quickly if you get the board pre-warmed, so that the mass of copper doesn't suck away the heat from the hot air gun. Plus with pre-heat, you've "only" got another 60-70C to climb with the gun, instead of >200C. Those Eval boards have an almost solid slug of 4oz copper on the bottom, plus a fair mass of solid copper on the other 3 layers too.
I've watched Terrell at work do it. He puts a hot air source underneath the PCB and heats it up for maybe a whole minute. Then, he hits the top of the chip with more hot air to get everything molten. It's not his favorite thing to do.
Actually, you might check-out that link anyway because an enterprising soul can sort of recreate several thousand dollars of expensive hot-air reflow equipment with a pair of $25 heat guns if due caution is used.
@VonSzarvas - video? Perhaps I will.
@JRoark - enterprising is my middle name.
BTW, I use a gas iron in hot air mode since it's nice and hot and doesn't blow anything away.
Then I used a small hobby heat gun and Chip-quick with ceramic tip tweezers.
Link to ChipQuik
Doc
Fixed!!!
Ah, I had googled ChipQuik and got the alloy description which seemed an appropriate reason to name it. Okay, so it was all about the heat then. Did you use the heat gun on top or underneath?
Both actually. The little gun I have is not heavy duty. I stole if from my wife's craft bin. ;-)
Wot!? Centipedes?
> Never heard of ChipQuik before. I'm assuming you used it just to ensure the legs lifted easy. It wouldn't have made any difference to the thermal pad, right?
Speaking as someone who seems to have an uncanny ability to let the purple smoke out of expensive components, I can tell you ChipQuik alloy is worth its weight in gold. Get some and play with it! Years ago I spent an afternoon with a tube of this stuff and an old PC motherboard and a heat gun. The lessons learned that day were priceless and continue to pay dividends today.
That stuff is amazing.
> In my youth I purchased a spool of In52/Sn48 solder, m.p. 118 deg C. (What is youth for if not to do stupid things?) Until today I hadn't considered using it to aid the desoldering of ICs. Thanks!
If memory serves, this stuff actually lets you solder to *glass*. Am I milking without a bucket here?
Great job on the repair.
For anyone looking for chipquik. It's been around for a while and works great.
https://www.chipquik.com/store/product_info.php?products_id=210001
I remember seeing it many years ago in the Jameco electronics product catalog.
https://www.jameco.com/z/SMD1-Chipquik-CHIP-QUIK-SMD-1-REMOVAL-KIT-SMD1-Chipquik_141305.html
You are exactly right. That's what I bought it for. I was trying to make my own x-ray tubes.