Soldering in new IC on old blue pcb woes - Page 1
Forum section: electronics / beginners

author: Quantumplate
author_rank: Regular Contributor
timestamp: July 08, 2023, 02:09:27 pm
content: Well, this is a problem..Removed the old ic by carefully snipping close to the body on one side of the chip. Then i simply flexed the chip using the other side's legs as a hinge until they snap - again close to the body so as not to dislodge the pads. Next i took my iron tip and removed all the leg remnants on both sides. On the side i flexed i have all the pads still nicely tinned, but on the side i sbipped, most of the pads are now bare, and despite copious flux and soldering attempts i can't tin any of those pads. You can kind of see in the photo, although it's a bit fuzzy.Never had to deal with a blue pcb module board before. What's the deal as they say?I'm using standard lead solder.Thanks

author: Quantumplate
author_rank: Regular Contributor
timestamp: July 08, 2023, 03:38:28 pm
content: I should add the bare pads are not the copper colour - they are grey. Conductive but not sure of the material.

author: Grandchuck
author_rank: Super Contributor
timestamp: July 08, 2023, 03:39:59 pm
content: A better picture would be good!

author: Ian.M
author_rank: Super Contributor
timestamp: July 08, 2023, 03:48:22 pm
content: The white edge and SIP header make me wonder if this is a ceramic substrate module?If so, the shockwave from snipping the pins may well have cracked the actual pads loose from the PCB, and whatever's left there isn't a solderable metal - it may even be a printed carbon layer used to allow the pads and traces to be selectively built up by electroplating.Incidentally some types of ceramic substrate module use screen-printed silver ink traces and pads, and it is then fired to fuse the silver to the ceramic surface, burn out the binder and sinter the silver particles leaving a continuous silver layer. Unfortunately this thin silver layer dissolves very quickly in ordinary solder, so you can't solder it unless you use an alloy contain several percent silver to slow down the rate it dissolves additional silver at, greatly reducing its tendency to eat the pads!

author: Quantumplate
author_rank: Regular Contributor
timestamp: July 08, 2023, 04:32:19 pm
content: Quote from: Ian.M on July 08, 2023, 03:48:22 pmFabulous info thanks a lot!I think you're right on the ceramic and the shockwave hypothesis. Boy am i stuffed now. I may be able to solder the side with the intact pads, but the other...i need some kind of tiny clamp, at least i don't see any other way. I can only laugh after spending a hundred hours on this unit!

author: Quantumplate
author_rank: Regular Contributor
timestamp: July 08, 2023, 08:16:28 pm
content: Quote from: Grandchuck on July 08, 2023, 03:39:59 pmI know. Best my tablet will afford.So i think after research some silver conductive glue could make this repair. But which one...do you happen to know the best type for ic work?

author: EPAIII
author_rank: Super Contributor
timestamp: July 09, 2023, 01:42:35 pm
content: Move the tablet closer or further away until the image is in focus. A tripod also helps. Or take several shots until one comes out clear.Quote from: Quantumplate on July 08, 2023, 08:16:28 pm