Exposed copper under lifted pad - Page 1
Forum section: electronics / beginners

author: blaugrana
author_rank: Newbie
timestamp: January 03, 2017, 08:41:09 pm
content: Hi! Please excuse my limited knowledge and a simplicity of my explaining, but I'd really like to get some answers as couldn't find an appropriate one.While cleaning the lifted pad area with a needle (I know I know), some of the brown (?) surface was scratched and a small dot-like copper surface was exposed. I made a new pad using a tinned cop wire and glued it with epoxy. I tried to solder the smd detail into its place, but it seems that the device (an mp3 player) still isn't working. So I have these following questions:1) Could that exposed copper be at fault?2) If so, how to fix it?(The attached pic isn't mine, just to add some visual).Thank you.

author: apelly
author_rank: Unknown
timestamp: January 03, 2017, 08:51:31 pm
content: It probably isn't useful to have a random pic from the internet.Perhaps you have a multi-layered board and you've soldered your new pad to an inner layer.Or perhaps it had a via in pad and you just didn't quite get the connection made.

author: blaugrana
author_rank: Newbie
timestamp: January 03, 2017, 09:13:15 pm
content: Let's say it's the first case. What's the solution?Can't get an actual picture for now. The device is Sandisk Clip+.

author: apelly
author_rank: Unknown
timestamp: January 03, 2017, 09:19:44 pm
content: Remove your new pad. Insulate between the pad and the inner layer. Replace the new pad and connect it to the trace that the original one was connected to.It's probably easier not to bugger about replacing the pad after you remove it. Just jump the IC leg to it's proper trace with some fine wire.How roughly did you hack about with that needle though? If you were digging through the fibreglass you surely would have realised.

author: blaugrana
author_rank: Newbie
timestamp: January 04, 2017, 12:45:21 pm
content: So I got the photo

author: argintviu
author_rank: Contributor
timestamp: January 04, 2017, 10:25:34 pm
content: Do you know what part the IC is ? (e.g. its name). Maybe looking at its datasheet will reveal where the leg with the missing pad should go.

author: poorchava
author_rank: Super Contributor
timestamp: January 05, 2017, 12:35:24 am
content: Well that for sure is a multilayer pcb. Even for basic stackups internal layers are usually close to the surface, so scratching tearing through to the internal layer is not unlikely at all.Sent from my HTC One M8s

author: blaugrana
author_rank: Newbie
timestamp: January 05, 2017, 03:58:34 pm
content: The IC is 74LVC1G3157GW. According to the datasheet (http://www.nxp.com/documents/data_sheet/74LVC1G3157.pdf) that pad is responsible for supply voltage. But for the love of it I just can't find where this pad's trace should go so I could use a jump wire.

author: whollender
author_rank: Regular Contributor
timestamp: January 05, 2017, 06:04:01 pm
content: It looks like it should go to the cap just above and to the left of the pin 1 marker. That definitely looks like a supply decoupling cap to me.

author: blaugrana
author_rank: Newbie
timestamp: January 05, 2017, 06:44:14 pm
content: Quote from: whollender on January 05, 2017, 06:04:01 pmThis one?

author: whollender
author_rank: Regular Contributor
timestamp: January 05, 2017, 06:51:42 pm
content: Yes. You can double check by doing a continuity test from the small amount of trace leading to the lifted pad (just a tiny bit of copper on the left side) to the capacitor, but it's probably not necessary.

author: blaugrana
author_rank: Newbie
timestamp: January 06, 2017, 12:05:53 am
content: Nice! Can't try it now as I don't have the IC with me. Will definitely report back.