I want to remove a 28 dual pin SMD device from a board and somehow attach a connector so I can route the pins to a proto shield. The SMD pad is really small (SSOP – Shrink Small Outline Package). This would be after removing the IC presently soldered there.
I see Sparkfun has boards to go in the other direction (DIP pins in PCB on one side and a SMD pad on the other side, like the BOB-00495). My problem is the opposite. I want to replace the SMD IC that’s on the original board with a connection to the proto shield.
I haven’t done any SMD soldering, but I’ve been watching the Sparkfun Chipquick SMD Removal and the Simon SMD tutorials, and I think I could work up to soldering something in.
For background, the IC is a PIC16 that reads some input and drives some relays. I’d like to replace the functionality of the PIC by being able to read and write to the pins from my Sparkfun RedBoard Plus. So jumpering over to the proto shield would let the fun begin…
Have a search for “28-pin SOIC Clip”. There are a few out there. Here is one example. Check it matches your chip package size and leg pitch before buying. That might be a good place to start?
In the past, I’ve done things like:
Use a sharp knife to cut the legs off the chip package - cut where the leg meets black chip body
Use an iron and solder wick / braid to remove the legs from the PCB a few at a time - much easier than trying to heat and flow the whole chip one one go
Find ribbon cable of the right pitch
Cut a square end on the ribbon cable
Use a sharp knife to cut through the insulation leaving the copper intact - cut about 2mm away from the end of the cable - cut top side, then bottom side
Use needle nose pliers to pull the strip of insulation off the cable
Tin the exposed ends of the copper wires
Solder carefully to the PCB pads
Tape or glue the ribbon in place
At the other end, separate the individual insulated wires, strip and solder (e.g.) to the short end of 0.1" header pins
Removing the chip is a matter of about 10 seconds of effort with one of these inexpensive hot air rework guns and a pair of tweezers.
I’ve been using the gun for years, with no failures that I can recall. Experiment with removing chips from discarded PCBs before tackling the one of interest, though.
To patch in to the newly exposed PCB pads, I usually solder on short bits of wire wrap wire.
I like the idea of the ribbon cable as there are 14 pins on each side.
I do want to point out that it’s an SSOP (Shrink Small Outline Package), where the pins spacing is half that of the SOIC package (0.65 mm vs 1.27mm). Do you think it’s still do-able? I think I’ll need to practice first with SOIC size.
On the test clip idea: unfortunately since the pad is SSOP they don’t seem to be available. That would definitely be my first choice even if it wouldn’t be a secure for long term operation.
Thanks for the suggestion jremington. Elsewhere on the board I need to connect two wires to thru holes that already have components installed. I tried using wire from my old spool of wire wrap and I couldn’t get it to stick. Perhaps you have some hints?
I ordered some low temperature soldering paste hoping that would tack it in place and flow better.
Got it. I have a friend who has a couple of nice microscopes for this sort of thing, and has offered to loan me one if needed. I think the limiting factor is my hands aren’t so steady. But will give it a try!