Flowable Silicone for PCB Repair

[Citroënbender]

While this relates to the core of another thread I felt it deserved airing on its own.

Years ago I "discovered" this product reading about the V6 ECU repairs by an English chap who clearly knew his stuff. Element 14 sell a product of this type specifically marketed as an electronics repair sealant. It's not cheap, the smallest quantity coming in at $70+ onto your doorstep.

Now I've seen there is available a "wicking" clear automotive silicone mainly targeted at problem leaks of glass and lighting elements. It's about 1/3 the price of the stuff at E14.

Can anyone comment on its interchangeability with the more expensive product?

[Duk]

So long as it's not acid curing silicone, it should be OK.

Maybe get some cheap, simple elcectronic thing off of ebay, scrub what ever coating off of the trace side of the board and coat it.
It would probably be fine if it's expected to work around plastic lenses.
Probably can't go soldering thru it, tho.

Incidentally, most ECU problems come from dried up or leaky electrolytic capacitors. So servicing of an ECU would mainly revolve around replacing the capacitors on the board.
Resistors should stay consistent basically for ever (a flippin' long time), diodes should also last basically for ever and the same for transistors. They either work or they don't. And if they don't, then you replace them.

[bazzbazz]

Alfa Romeo Engine ECUs don't have Electrolytic Capacitors, they use Surface Mount Multi layer Ceramic Capacitors. But your right as the capacitors being the problem, usually to faulty solder connections.

As for the transistors, the main power transistors under the gel are not the usual semiconductor 3 legged packages that most are familiar with with, but the actual transistor "Die's" that are about 1mm square and are gold soldered to fine wires the thickness of your hair.

If the ECU has a problem other than a loose capacitor or faulty solder joint, its pretty much FUBAR. They were never intended to be repaired/reworked.

Remember I am only referring to the Alfa ECU construction.

[Colin Edwards]

Need to be very careful when removing and reinstating conformal coatings.  Depending on the type of coating, removal is either via a solvent or mechanical / abrasive. 
If the coating can be chemically removed, repair can be successful.  However if the coating can only be removed mechanically, the board was probably never intended as a serviceable item. 
These coatings are applied to increase the reliability of a pcb.  Usually the more hostile the environment, the more comprehensive (and permanent) the coating.  Given the vibrations and heat cycles a ECU experiances, the coating will be intended to provide mechanical suport of components in addition to the electrically conductive connections.  If the incorrect coating is used or poorly applied, a perfectly good PCB will eventually fail.  A coating with a high coefficient of expansion will in time lift components from the PCB.  A coating with low thermal conductivity will prevent components from losing heat.
A pcb must be designed with the environment and eventual coating clearly defined.  I'd  be very careful applying a coating of unknown performance to a freshly repaired PCB / ECU.

[Citroënbender]

I was looking at the possible scenario of replacing a damaged 104-pin EEC-V header on a board covered with flowable silicone and further bonded to the "ribs" of its casing.  This would have required mechanical removal of enough coating to de-solder.

Having re-thought my problem (2/104 pins at fault) it seems more intelligent to use the reflashing port to pass a couple of new wires through, and "plumb up" using a simple AMP 2-way weatherproof plug set. That's 102 solder joints I have no need to disturb, and a bunch of silicone sealant also unmolested.

So, to secure the new wiring I'll probably just use a couple of spots of neutral cure caulking silicone over the top of the fancy stuff.