Any tips on how to desolder this thing? - Page 1
Forum section: electronics / beginners

author: requim
author_rank: Regular Contributor
timestamp: January 02, 2012, 08:52:07 pm
content: I have had no success trying to desolder these two chips. I've used my hot air gun on both high and low with no success, and I even spent a few minutes trying with a soldering iron after that. As you can see the only success I've had is destroying the plastic housing. If I didn't know better I'd think it was part of the board but it obviously isn't. I'm at a loss for how to proceed unless the answer is an X-acto knife or something. I thought they might be glued (which they probably are), but from what I've read if I heat them up, let them cool and then try to pry them off they should break free, but that hasn't worked either.I'd appreciate any hints, tips, or suggestions. Thanks!

author: FenderBender
author_rank: Super Contributor
timestamp: January 02, 2012, 09:00:22 pm
content: Which one? Well I'd tried solder braid, a lot of flux, and maybe even apply some solder onto the existing joints for better heat transfer.

author: requim
author_rank: Regular Contributor
timestamp: January 02, 2012, 09:06:15 pm
content: Resized the picture for easier viewing.. The two white ones... It's a double sided six-layer smd board so I can't do anything via the backside either..

author: FenderBender
author_rank: Super Contributor
timestamp: January 02, 2012, 09:08:37 pm
content: Oh...Well I can't really even tell what they are from the picture. At first glance they looked like a big SMD passive like two big SMD ceramic caps, but ..uh?

author: FenderBender
author_rank: Super Contributor
timestamp: January 02, 2012, 09:09:25 pm
content: If they are really chips, they have to be some sort of BGA package because I see no pins. Might want to try a little more hot air. Why do you need to remove them?

author: requim
author_rank: Regular Contributor
timestamp: January 02, 2012, 09:19:11 pm
content: The chips are similar to the two black ones down below it. And I need to remove them because I need to replace them. At this point there is no question they have to be replaced since they've been damaged/destroyed in the attempted removal process.Yes they are SMD, and I've let hot air blow on them for quite some time with no success. I'm afraid if I let it go any longer I'll permanently damage the board. How high of heat and how long can I let it go for? They started to melt after I had the heat gun on high for 30 seconds or so. So I switched back to low heat (~310 celsius) with no success.

author: jahonen
author_rank: Super Contributor
timestamp: January 02, 2012, 09:20:45 pm
content: I think you have just experienced the joy of multilayer board repair work. They sometimes require huge amount of heat to reflow the solder, due to massive planes buried inside the PCB. You could try to preheat the board to about 100°C and then use proper hot air soldering tool while applying the preheat. That should do the job.Regards,Janne

author: requim
author_rank: Regular Contributor
timestamp: January 02, 2012, 11:03:12 pm
content: Turns out you were right. I just needed to set the heat gun on the chips on low for a longer period of time. Came off without issue.I know it's not good to expose chips to high heat for long, are there any sort of guidelines or rules of thumb to follow?

author: Tony R
author_rank: Regular Contributor
timestamp: January 02, 2012, 11:50:09 pm
content: Quote from: requim on January 02, 2012, 11:03:12 pmRead the data sheet and use an infrared thermometer

author: Unknown
author_rank: Unknown
timestamp: January 03, 2012, 12:51:02 am
content: Does any manufacturer specify desoldering in their data sheet?

author: IanB
author_rank: Super Contributor
timestamp: January 03, 2012, 12:53:17 am
content: Quote from: alm on January 03, 2012, 12:51:02 amI think they often give a soldering time/temperature profile. If you stay within those time/temperature limits when desoldering I presume you will not harm the device?

author: Unknown
author_rank: Unknown
timestamp: January 03, 2012, 12:54:27 am
content: Except that they've already gone through that profile during soldering, and it's usually only guaranteed to survive it once. Not to mention resoldering the part in the future.

author: Mechatrommer
author_rank: Super Contributor
timestamp: January 03, 2012, 05:34:35 am
content: even if you see the solder is melting (on top), but its not necessarily the case on the bottom (pcb), so in soldering process, heating up the solder to melting point only is not enough (on visible top), you need to heat up the base (pcb) as well to the melting point. once you get a melted solder at least in one plan inside the solder blob, then you can pull out that particlar point, but in bga case, you need to make sure the process above will reach into the centre joint which will receive the heat last. so in order to achieve that you need either two step 1) high temp. gradient (hi gun temp setting, which could damage the chip) or 2) use lower temp setting and wait long enough (patient) until all the portion is in temp equilibrium.

author: requim
author_rank: Regular Contributor
timestamp: January 03, 2012, 09:06:45 am
content: @Mechatrommer -Yes I destroyed the two chips by using the heat gun on high after it wasn't working on low. But when I successfully removed them it was because I took the heat gun and set it on low and ran it for a longer duration (30-60 seconds?). Came right off.. I guess I'll do something similiar in reverse when I go to put the replacement parts back on. I guess I should use solder paste? Or can I get away with putting solder on the chip and then soldering it to the board? How is it done in the factories?

author: Zad
author_rank: Super Contributor
timestamp: January 03, 2012, 05:29:48 pm
content: If the devices are BGA, the tiny balls are themselves blobs of solder. In factories they just place them over the pads and put it in the reflow oven. If the chip is required to be used again (for whatever reason) then they have to be "reballed" which is not my idea of fun.

author: w2aew
author_rank: Super Contributor
timestamp: January 03, 2012, 06:47:41 pm
content: Quote from: requim on January 03, 2012, 09:06:45 amAs mentioned elsewhere, if they are BGA parts, then the new parts will have solder balls already attached. If it is some sort of leadless SMT part, then solder paste is usually screened onto the board before reflow. Either of these types of parts - especially the BGA parts, have very specific temperature profiles that are specified to be followed for proper soldering - something that is typically difficult to reproduce without the proper equipment.