BGA manufacturing fix - Page 1
Forum section: electronics / projects

author: Bababooey
author_rank: Contributor
timestamp: August 26, 2015, 03:02:08 pm
content: Hi,I made a mistake on a prototype run of pcbs and would love to get suggestions on how I can fix it during assembly.I forgot to make a connection between two of the pins on the BGA chip you see in the picture. My initial thought was to create a solder bridge between the two balls, but my assembly house is telling me that it is a risky operation.Any thoughts? Thanks!

author: plazma
author_rank: Frequent Contributor
timestamp: August 26, 2015, 03:12:44 pm
content: I would modify the pcb. You can connect the pads with very thin wire. It have been done where I work. You can even swap pads with wire and epoxy.How many do you need done?

author: miguelvp
author_rank: Super Contributor
timestamp: August 26, 2015, 03:16:16 pm
content: What is the chip and could you connect them by programming?

author: Bababooey
author_rank: Contributor
timestamp: August 26, 2015, 03:46:11 pm
content: Quote from: miguelvp on August 26, 2015, 03:16:16 pmIt's a CSR chip, and the pin I forgot to connect toggles the programming interface on and off, so sadly without fixing it I wont be able to program the boards all.Quote from: plazma on August 26, 2015, 03:12:44 pmThank you for the suggestion, I'll contact them and check if they are up for it. Luckily it's only 10 pcbs, and at this point I'm happy if I can get one of them working.

author: plazma
author_rank: Frequent Contributor
timestamp: August 26, 2015, 03:50:45 pm
content: You can also connect them after assembly. I have done it with hot air rework station and thin wire. Two rows from the side can be connected with wires.

author: Bababooey
author_rank: Contributor
timestamp: August 26, 2015, 03:58:01 pm
content: Quote from: plazma on August 26, 2015, 03:50:45 pmI'll keep that in mind. It's a small 79-pin, 4.8mm x 4.8mm WLCSP chip - so I'm not confident I can place it by hand. Or do you mean melt the solder and stick the wire in between from the side without removing the chip?I'm considering ordering a small pcb to place in between the WLCSP footprint and the chip, with that one extra connection. But I'm not even sure if that can be done.

author: plazma
author_rank: Frequent Contributor
timestamp: August 26, 2015, 04:00:59 pm
content: Yes, heat locally so the bga balls melt and stick the wire into the solder balls.

author: miguelvp
author_rank: Super Contributor
timestamp: August 26, 2015, 04:11:02 pm
content: Can you pre-program them before assembly with a CSP Test & Burn-in Socket? I know they are pricey but is it a possibility to program them before assembly?

author: Bababooey
author_rank: Contributor
timestamp: August 26, 2015, 04:28:19 pm
content: Quote from: miguelvp on August 26, 2015, 04:11:02 pmI'm considering it. But then I have to be 100% sure my usb boot loader code works, considering I wont have the option to re-program them later.

author: nctnico
author_rank: Super Contributor
timestamp: August 26, 2015, 06:26:09 pm
content: I have drilled holes through PCBs in order to put forgotten BGA connections in place. I would not recommend wanting to do this for 10 boards though because it is like doing brain surgery on an ant.If the boards are still bare I'd just respin the boards. Probably the cheapest option.

author: Bababooey
author_rank: Contributor
timestamp: August 26, 2015, 07:10:05 pm
content: Quote from: nctnico on August 26, 2015, 06:26:09 pmHaha, that's a great analogy. It would require laser drilling so I can't say I'm tempted to try that.Yes, you are probably right. But they are ~$1100USD boards, so figured it's worth thinking about alternative solutions before deciding to respin them.

author: krish2487
author_rank: Frequent Contributor
timestamp: August 26, 2015, 07:33:29 pm
content: You can at the very least attempt to "fix" a board or two by thishttp://www.ebay.com/itm/Intel-CPU-Socket-LGA-771-775-Adapter-Mod-Sticker-Upgrade-Core2-to-Xeon-Quad-/281549863113?hash=item418dadf8c9second imageNot directly of course, but sort of replicate it using thin single strand 26 / 28 gauge wire and kapton tape.Of course, if the LGA775 pitch matches your BGA then nothing like it!!!($1100 is a lot of money and no reason why you can't hack it, after all thats what gives us engineers our edge.. ;-) )

author: Bababooey
author_rank: Contributor
timestamp: August 26, 2015, 07:45:16 pm
content: Quote from: krish2487 on August 26, 2015, 07:33:29 pmWoah, I have never seen something like that before. That's genius. Thanks!!

author: nctnico
author_rank: Super Contributor
timestamp: August 26, 2015, 07:49:20 pm
content: Quote from: Bababooey on August 26, 2015, 07:10:05 pmLaser drilling isn't required. It depends on what is on the other side and inner layers. I usually start with a 2mm router bit to create a trench and then drill to the BGA ball with a smaller diameter drill. Then the fun part starts where I use a piece of solid wire wound on a soldering tip to create a long and thin soldering tip to solder a hair like enamel wire to the BGA ball.

author: John_ITIC
author_rank: Frequent Contributor
timestamp: August 26, 2015, 08:16:29 pm
content: Quote from: Bababooey on August 26, 2015, 03:02:08 pmI recently did something similar, where I needed to connect some balls under my BGA. I used this:http://www.circuitmedic.com/products/201-3130.shtmlYou essentially have to put down a thin 5 mil track, tack solder to pads, epoxy it in place and finally reflow your IC.http://www.circuitrework.com/services/bga.shtml

author: Bababooey
author_rank: Contributor
timestamp: August 26, 2015, 08:23:39 pm
content: Quote from: John_ITIC on August 26, 2015, 08:16:29 pmAnother great suggestion, thank you. Did you do it yourself or use Circuit Technology Center? Any idea how much they would charge for something like this?

author: langwadt
author_rank: Super Contributor
timestamp: August 26, 2015, 08:47:06 pm
content: Quote from: krish2487 on August 26, 2015, 07:33:29 pmI don't think you'd need tape, just stick a tiny piece of the thinest wire you can find in the solder paste like if it was a component, and then place the bga

author: John_ITIC
author_rank: Frequent Contributor
timestamp: August 26, 2015, 09:35:10 pm
content: Quote from: Bababooey on August 26, 2015, 08:23:39 pmI did it myself since I have a BGA rework station. I never asked them for a quote.

author: Bababooey
author_rank: Contributor
timestamp: August 26, 2015, 10:34:27 pm
content: Quote from: John_ITIC on August 26, 2015, 09:35:10 pmThank you internet for all the helpful answers. I brought up the PCB repair solution to my assembler and they told me they actually work with a company that does a similar thing. I'm in the process of getting a quote now.

author: krish2487
author_rank: Frequent Contributor
timestamp: August 27, 2015, 05:37:11 am
content: The kapton tape is just insurance against the thin wire accidentally shorting to adjacent BGA balls. It can be done without, but I sleep more peacefully knowing that a small shock, bump, drop, push won't accidentally cause the board to stop functioning.Quote from: langwadt onTodayat 06:47:06 AM

author: SaabFAN
author_rank: Frequent Contributor
timestamp: August 27, 2015, 11:43:37 pm
content: Have you considered conductive paint?Back in the days of Athlon XP-Processors with T-Bred core, they could be overclocked by reconnectingtinycuts made on the processor and unlocking the multiplier again. I applied the paint on my CPU with a toothpick and it worked instantly.IDK if the paint can withstand the heat of a reflow-process though.

author: 0xfede
author_rank: Regular Contributor
timestamp: August 28, 2015, 07:44:50 am
content: Hoping that I'm not coming too late but you could use a low eutectic alloy such as chipquik (or the ones with high content of lead), your iron around 140 degree celsius and small AWG30 wirewrap tinned wires (I would recommend R30Y-0100).It's an alternative that should made after the board production such as the conductive paint.I used this technique several times for messed proto with always good results.Just my two cent.

author: 0xfede
author_rank: Regular Contributor
timestamp: August 28, 2015, 07:58:58 am
content: I just realized that probably you have no access on the bottom of the board to these pads.Sorry.

author: Bababooey
author_rank: Contributor
timestamp: August 29, 2015, 08:14:39 pm
content: Update: I checked with various companies and it costs between $50-$100USD per board to professionally add the missing track. Mostly the same prices, lead time varies.