Missing pads - salvagable? - Page 1
Forum section: electronics / beginners

author: abcd12
author_rank: Newbie
timestamp: March 12, 2022, 02:14:35 pm
content: Hi,my Xperia XZ2 Compact sim card reader had bent pins so I decided to replace it (my first microsoldering/desoldering work so bound to end in a disaster). I used a hot air gun to remove the reader and in doing so I accidentally pulled off two soldering pads. Is the phone still salvageable (pic in the attachment)? I'm not sure if there are any vias under the missing pads.

author: golden_labels
author_rank: Super Contributor
timestamp: March 12, 2022, 02:55:53 pm
content: First check if those pads were actually used for anything. If not, you may leave them not connected. If that was only a ground connection for the reader’s case and it’s already connected to multiple other places, you may also leave it out.If there were vias there, I do not think you can fix that without an effort and equipment not suitable for rescuing a mobile phone.Otherwise: you can bodge whatever uses the missing pad to a part of a track that still remains nearby:I do not see any traces going anywhere from the missing pads, so I assume they were connected to the SMT components on the right. You can solder directly to those parts. Just be careful to not overheat those, which will not be easy with pitch that small.By using a piece of wire as a bridge. You may either solder that to the closest track available or — if a long wire is not an issue in this case — to any available pad elsewhere. For bridging traces directly, you may see Dan’s of New Retro Repair video on that topic:I have seen there are copper stickers that you may use as pads. You supposedly glue them where the pad should be, bridge to the trace and voila. I never used those and I am not sure how well they deal with temperature and aging.None of the above methods will be easy to apply at that scale. The components and traces are tiiiiiny. So take you time. It will not be a one-evening job. Possibly even test on some donor boards first. I never fixed something that small myself and, if you do fix that nicely, you have my respect for doing surgery of that kind.

author: abcd12
author_rank: Newbie
timestamp: March 12, 2022, 06:50:02 pm
content: @golden_labelsThank you very much for the detailed explanation.

author: abcd12
author_rank: Newbie
timestamp: May 12, 2022, 10:50:30 am
content: So, I just managed to somehow reattach the missing pads. Of course in the process of doing so, I accidentally desoldered (and lost) one resistor (red rectangle).First of all, was it a resistor (if you compare the current picture with the first one - right side)? The adjacent two resistors have a resistance of 200 and 1500 ohm, respectively (from left to right, yellow rectangles). Can I try (without doing further damage - the phone still powers up) one or the other resistance?

author: Fraser
author_rank: Super Contributor
timestamp: May 12, 2022, 12:00:57 pm
content: I would not have recommended working on a mobile phone as your first step into micro reworking but you are where you are.Sadly large amounts of hot air can cause quite a lot of collateral damage with components being cooked, moved or even blown off the PCB. I note some areas on the left of the PCB that would concern me. There looks to be missing components and PCB pads along with displaced components. At the bottom of the picture there could be a solder splash but that could just be a lighting effect in the image. Picture attached.The pads that you tore on the SIM card connections may use PCB Vias to make contact with an internal layer of the PCB. These can be challenging to restore such they will survive the resoldering of the SIM card module.Good luck, but I think you are in for bit of a rough ride getting that phone working againFraser

author: abcd12
author_rank: Newbie
timestamp: May 12, 2022, 02:22:20 pm
content: @FraserThank you for the reply. I agree, it was a massive task but I just had to try.Anyway, the picture looks pretty bad, partly due to the low resolution (resistors, capacitors are not (hopefully) fried, it's black soldering mask that I couldn't get off). As far as I can tell, only one resistor is missing. However, I have no idea what the resistance value of the original was. What can I do? Assume it's the same as one of the adjacent ones (which differ)? Or can I just try and see what happens if I don't put it back? Can I damage something by doing that?

author: macboy
author_rank: Super Contributor
timestamp: May 14, 2022, 03:22:59 pm
content: You said Black solder mask. Clearly the solder mask is green in the first photo, and looks clearly black in the second. You have absolutely charred the board by using far too high a temperature. Even slight discoloration of the solder mask indicates too high a temperature. Blackened is in another realm of damage. It is dead. There is no chance of saving it now.

author: abcd12
author_rank: Newbie
timestamp: May 20, 2022, 06:39:47 pm
content: No, there seems to be misunderstanding. I used black UV curable solder mask in order to reattach the missing pads (as shown here). I have been able to reattach the sim card holder and there is continuity between missing pads/pins and nearby resistors, however the sim card is still not detected. I would like to resolder the missing resistor, I just don't know what the resistance was.