Removing TQFP-128 Package with Thermal Pad from Double-Sided Board - Page 1
Forum section: electronics / repair

author: cosmicchasm
author_rank: Newbie
timestamp: May 30, 2024, 05:49:46 pm
content: Hey all,I'm looking for some advice on how to remove a TQFP-128 chip with a soldered thermal pad from a 6-layer double-sided PCB.There are decoupling caps within millimeters of the thermal vias underneath, which I thought would complicate things if I decided to use a preheating gun. I've secured those to the board with kapton tape. On the top layer where the chip is soldered there are plenty of smaller components around there which I've also secured with kapton tape.Problem here is that I don't really have too much experience with SMD rework, and this problem seems to be a huge one for me to tackle with my lack of experience. I do not currently have access to a hot plate and only have a reflow oven and a heat gun.Could I put the board into the reflow oven and preheat at 150 C then take it out and blast it with the hot air gun?Any tips? Thank you!

author: selcuk
author_rank: Frequent Contributor
timestamp: May 30, 2024, 07:47:11 pm
content: You can use hot air gun and a piece of thin metal sheet. Check this answer from an old topic. May be you can use kapton tape to build the wall.https://www.eevblog.com/forum/repair/bga-chip-replacement-when-board-is-difficult-to-heat/msg5274463/#msg5274463Quote from: selcuk on January 12, 2024, 10:15:16 am

author: wraper
author_rank: Unknown
timestamp: May 30, 2024, 07:52:25 pm
content: The trick with capacitors on the bottom (if solder melts) is them not touching anything, then they'll stay in place regardless. Kapton tape may actually move them or even pull them off. The only reason to shield anything around the chip is to protect heat sensitive plastic connectors or electrolytic capacitors around the chip if there are such. Or protect small components against knocking them off the board if you remove the chip with shaky hands and they are in very close proximity.

author: cosmicchasm
author_rank: Newbie
timestamp: May 30, 2024, 08:41:06 pm
content: Hey there,Thanks for the helpful advice. My boss needs this board repaired soon for a conference this fall. I got the chip off but also managed to snag/damage some of the pads along with the chip.Now this question becomes more like this: How could I repair these pads? They're super small and some are on high-speed traces.Don't really want to give up on this board but I also might not be able to repair it.

author: selcuk
author_rank: Frequent Contributor
timestamp: May 30, 2024, 09:15:00 pm
content: Repairing the pads can be harder than desoldering the chip. You can watch this video to have an idea. There are many similar videos on the internet. I usually extend torn tracks with wires on top or bottom on IC lead and solder them but I think your IC have very small pads. So finding ready made pads like in the video may be better.https://www.youtube.com/shorts/4LWDsRMUdEQ

author: wraper
author_rank: Unknown
timestamp: May 31, 2024, 05:45:22 am
content: Just run very thin wires instead of those traces, i usually take them from multi-strand wires with thin strands. If they cone from under the chip, solder them first, then the chip, and terminals above those wires. UV curable solder resist can help fixing them in place.https://www.amazon.com/Solder-KGX%E2%80%91900-Resist-Electronic-Components/dp/B09WF4DWPN. If they come from the outside, solder them after soldering the chip. TQFP should be relatively easy, I've done that even under fine pitch BGA.