Hmmmmm, nasty crack but eminently repairable in my experience.
You would need to desolder the components that bridge the crack. Then complete the crack 'circle' with a knife and remove the 'island' complete.
Using a microscope, inspect the edges of the island looking for the tracks. Sometimes the edge needs to be cleaned up with a light sanding. A Dremel multitool may also be used to step down through the layers at the edge of the island. Once all PCB tracks have been identified, the dremel tool is used to reveal them enough for soldering Kynar jumper wires. The same is done to the main PCB so that the Kynar jumpers can straddle the gap between it and the island. It is important to slightly raise the island above the main PCB, like a daughter board to enable the Kynar wires to be soldered around the edges. A support structure will need to be constructed but that is purely a mechanical challenge. Once all wire links are in place, the island may be lowered to within a couple of mm of the main PCB where is needs to be fixed in place using epoxy or some such mechanical fixing method. The jumper wires just sit underneath. The components that stradle the crack will need to be adjusted or modified to fit the slightly elevated island. Wire wrap sockets with their cong legs may be used for chips. Components with longer leads may be required or SMT replaced with through-hole technology.
An alternative approach once the various PCB tracks have been identified is to prepare the island and main PCB edges and attempt to link the tracks using very short lengths of thin tinned copper wire. This can be challenging depending upon the layout of the multi layer tracks.
If the multi layer tracks are too close together at the edge of the PCB, you can use continuity checks to locate their connection points on components. The jumper wire may then be connected to the component leads instead of to the PCB tracks. In some cases this is a far better approach to the problem. You end up with somewhat of a spiders web of Kynar wire, but it works.
This sort of repair is the sort of thing I used to do for the fun of the challenge...... People said the PCB's were beyond repair...... I proved that to not be the case. Some equipment I repaired had been deliberately damaged wiih a hammer blow through the middle of the main PCB. Unrepairable ? No, provided no unique or custom chips had been destroyed. If you really want to wreck kit, you smash up the silicon
I might add that this sort of repair is reserved for non mission critical applications such as data recovery or, as in your case, a desire to bring a unit back from the dead.
Another hint, I used to buy brass tube, rod and hollow box section from the modelling shop. I used it to create temporary or permanent scaffold for the island PCB The brass solders easily and is pretty rigid. I used the brass to reinforce the epoxy joining of the PCBs by so,dering to the ground plane copper. I never had a repair fail and the PCB strength was maintained.
One for a rainy day maybe ?
Fraser
Home
Help
Search
Login
Register
