Tips for preventing lifting of SMD Pads - Page 1
Forum section: electronics / beginners

author: gjh
author_rank: Contributor
timestamp: April 11, 2022, 08:57:14 am
content: Recently I just scored a free microscope so now I can actually do SMD repairs. Have a straight forward repair for my mechanical keyboard have some lifted up pads on the usb connector. I'm finding that its very easy to lift and destory pads when using my Hakko 888 @ 280c to 320c degrees, I normally don't have a problem with other boards.Any tips or tricks to prevent pad lifting. of course Im using plenty of rosin flux. Thinking it's probably safer to use my hot air gun. Anyways plan on restoring the pcb pads,and epoxy them for practice even though I will be using a bodge wire to change USB mini B to USB C (breakout board)For another board I also have a QFN package that I could never get right, now with a microscope I can see Im not properly forming connections. With that board never had a problem with lifting PCB boards. Have to figure out proper technique for QFN package though.

author: ledtester
author_rank: Super Contributor
timestamp: April 11, 2022, 09:42:04 am
content: Quote from: gjh on April 11, 2022, 08:57:14 amWhat is your keyboard PCB made of? Can you post a pic?

author: jmelson
author_rank: Super Contributor
timestamp: April 11, 2022, 04:06:18 pm
content: For best results in terms of saving the board, I cut the leads off the bad chip and then "sweep" all the leads off the board's pads. I use an X-acto knife to score the leads near the body of the chip, then break the leads by using the knife blade like a wedge to snap the leads free of the body. On the 4th side of a square package, I just bend the body up and down a few times until the leads snap at the score mark.Of course, this doesn't help if you want to salvage the chip. But, it greatly reduces the chances of lifting a pad.I don't have a hot air machine in my home shop, but do at work, and it is quite amazing.Jon

author: tooki
author_rank: Super Contributor
timestamp: April 11, 2022, 05:58:53 pm
content: Quote from: gjh on April 11, 2022, 08:57:14 amThat temperature might be toolow. As evb149 said, you want a complete melt in 2-3 seconds. Dwelling longer risks delamination. The best is preheating, second best is increasing the iron temperature a bit.Quote from: gjh on April 11, 2022, 08:57:14 amA modern gel flux may give better results.

author: gjh
author_rank: Contributor
timestamp: April 12, 2022, 09:16:16 am
content: Quote from: ledtester on April 11, 2022, 09:42:04 amHeres a pic of the keyboard pcb, it just seems ridiculously easy to lift pads on the board compared to others.Im currently using 60/40 SnPb solder. Friend just gave me some solder for free but lead free. 95.5SN/3.8AG/.7CU & SN100C Probably prefer not to use that.I have MG Chemicals #425 fine wick and Quick Braid rosin wick which is twice as wide. Never really got the hang of drag soldering. might pick up a concave hoof tip for the Hakko currently using a wedge tip think its 1.6mm. Friend has given me some 0.8 wedge tips and some big 1.0mm nozzle. (a1005) Is it worth trying a smaller wedge tip ?

author: tooki
author_rank: Super Contributor
timestamp: April 12, 2022, 06:35:03 pm
content: I have a different theory: you’re not lifting the pads with heat at all, they were already loose or at least weakened.I have some mechanical keyboards which developed intermittent connections because pads tore offdue to mechanical force during ordinary use. Single-sided phenolic board (i.e. the cheapest possible), and the force of a keystroke is precisely in the direction to rip the pads off.If the keyswitches were not FULLY under tension when soldered, then each keystroke pushes on the pad a little bit.This problem wouldn’t happen with a board with plated through-holes, since each keystroke presses into the top side pad (not to mention the plated hole itself).On mine, I had to resolder many pads (while keeping them under tension so any force “at rest” is pulling the pad towards the board, not away) with a couple of bodge wires to reestablish continuity.

author: gjh
author_rank: Contributor
timestamp: April 12, 2022, 11:26:40 pm
content: Quote from: tooki on April 12, 2022, 06:35:03 pmI did rip up half a pad just by removing a bodge wire that was a little too thick, did apply very little pressure on the joint preparing to lift the wire as the solder melted... surprised me while i was being careful. now I have 0.2mm enamel wire to do proper bodge wiring. was thinking its just a cheap board.

author: tszaboo
author_rank: Super Contributor
timestamp: April 13, 2022, 10:36:35 am
content: My general advice against pad lifting: Get yourself a quality manufacturer. I had pad lifting issues with boards coming from Asia, never had the same issues with the ones made in Europe. Those 10 dollar boards are suddenly very expensive if you need to rework them.

author: gjh
author_rank: Contributor
timestamp: April 13, 2022, 12:56:02 pm
content: Quote from: tszaboo on April 13, 2022, 10:36:35 amIt's a Leopold Korean mechanical keyboardActually for the first time I got some boards made up @ JLCPCB for a new project. previously I would have made my own at home a very long time ago.I just found a hoof tip in my spares box, might give that a go for drag soldering.

author: ledtester
author_rank: Super Contributor
timestamp: April 13, 2022, 02:53:45 pm
content: You could also replace it with a pigtail connector (with the appropriate strain relief), e.g.:Just scrape away the solder mask to create new pads somewhere on the board.

author: gjh
author_rank: Contributor
timestamp: April 13, 2022, 04:16:04 pm
content: Quote from: ledtester on April 13, 2022, 02:53:45 pmGood point. I was going for USB-C breakout board with a ton of hotsnot (hotglue) to keep it in place behind the shell.

author: tooki
author_rank: Super Contributor
timestamp: April 13, 2022, 04:59:07 pm
content: Quote from: tszaboo on April 13, 2022, 10:36:35 amWhen buying an off-the-shelf product, one doesn’t typically have the ability to specify the PCB type and supplier.

author: strawberry
author_rank: Super Contributor
timestamp: April 13, 2022, 07:53:30 pm
content: for modern PCB dont use gas torchlow temp 250C for PCB older than 20y

author: gjh
author_rank: Contributor
timestamp: April 13, 2022, 11:37:41 pm
content: Quote from: strawberry on April 13, 2022, 07:53:30 pmI prefer to use my corded Hakko FX-888D at home.. For gas powered soldering I would leave it where I'm in a remote location with no power

author: Shock
author_rank: Super Contributor
timestamp: April 14, 2022, 01:27:30 am
content: Flux and preheating, if the board or component is challenging low temp alloy and reflow the joints then remove.

author: gjh
author_rank: Contributor
timestamp: April 14, 2022, 03:40:47 am
content: Quote from: Shock on April 14, 2022, 01:27:30 amI can preheat using my 3d printer heat bed I guess.

author: tooki
author_rank: Super Contributor
timestamp: April 14, 2022, 05:32:49 am
content: I don’t think that will help, since I don’t think the problem is your technique. I think the pads are already damaged and you’re going to have to do pad repair either way.

author: Shock
author_rank: Super Contributor
timestamp: April 14, 2022, 11:48:02 am
content: Those techniques I mentioned are if you are using too much heat for too long a time, too little heat for too long a time, or taking multiple stabs.Obviously if it's the pcb, age, stress or corrosion they may not help. But those techniques are good to know regardless as they reduce prolonged higher temps which is one of the common reasons pads lift during rework. Best to test on scrap boards first and get the techniques down.Smd components can sometimes be moved mechanically in a certain direction or by applying a little pressure and rotating (rather than pulling up) while being removed to reduce pad lifting.

author: gjh
author_rank: Contributor
timestamp: April 15, 2022, 05:25:26 am
content: I just switched over from a 1.6mm Taiwan made tip (Lomen) to a proper Hakko 0.8mm wedge tip.. 0.8mm is alot easier to work with and more friendly to the PCB at this stage.. finding it harder to damage tracks with 0.8mm @ 280c

author: gjh
author_rank: Contributor
timestamp: April 18, 2022, 11:26:32 pm
content: Did a successful repair. I guess my issues to lifting pads were helped by using narrower tip, and not to use too large gauge wire. (previously I just used scrap wire I had around instead of proper 0.25mm enamel copper wire). I put in a usbc breakout board in replacement of the usb mini b connector and hot glued it in place.. seems pretty solid but need to be careful when plugging in and out.Thanks all for your input!