Best glue for cracked circuit board?

[Flighter]

Hi all.

I'm looking for recommendations to glue a crack in what looks like printed circuit board substrate.

The part in question is a component of the Olympus OM2 mode switch and is badly cracked on the leg on one side with a crack beginning on the leg on the other side, as shown below.

The recess between the two legs, indicated by the yellow arrow in the above picture (10mm is approx 4/10ths of an inch), meshes with a tab projecting from the bottom of the mode switch (indicated by the yellow arrow in the picture of the the underside of the top cover below)…

…and a tab on the rest of the mode switch mounted on the main body of the camera (yellow arrow again below).

The legs are therefore subject to a degree of lateral force either side as a result of the operation of the mode switch and I'm not sure what adhesive to use.

I would like to try gluing it first rather than making up a new piece of pcb substrate and then having to rivet the metal contact to it.

 

[koraks]

Try either cyanoacrylate (superglue) or epoxy. With epoxy you can build a droplet around the break that might give a little more sturdiness. If the pieces still fit together seamlessly, cyanocarylate may produce a better bond.

 

[Flighter]

Thanks koraks, although badly cracked the legs haven’t parted company yet, so hopefully the cyanoacrylate will wick into the cracks.

 

[Dan Daniel]

Is there clearance to add a layer of reinforcement? Even a clear plastic from a package of batteries or such laminated to the blank side would add strength.

I've always had better luck with mechanical reinforcement as part of a repair, not just adhesives. But of course it isn't always possible.

 

[BobUK]

It looks like paxolin to me.

If so, the following link suggests slow setting Araldite to be the answer.

Best adhesive for paxolin - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum

Best adhesive for paxolin Vintage Radio (domestic)

www.vintage-radio.net

 

[Flighter]

Thanks Dan, there might be room for a very thin sheet, I suspect that there is very little clearance above the plate beyond the thickness of the rivets. Maitani-san didn't leave much free space in his creations. A further problem is the thin head of the securing screw has quite a large diameter so there is very little space between the edge of the screw head and the end of the slot made by the two legs. But every little helps.

 

[Flighter]

Thanks Bob, I'll have a look at that post, my Dad was a great believer in Araldite. The stuff I know is quite viscous so might be difficult getting it into the crack.

 

[Dan Daniel]

There are some solvents that will thin some epoxies. You might try a couple. Acetone would be my first try. Look at the assorted writing on the epoxy and see if a particular solvent is mentioned for cleanup- that's the one!

 

[runswithsizzers]

Unless the epoxy manufacturer specifically recommends it, I would avoid adding solvents. All epoxies can be made thinner by warming them. Of course warming epoxy shortens your working time before it hardens -- which can be either good or bad, depending on the complexity of your assembly. And for anyone who needs thin epoxy, there are several low viscosity formulations available that are 100% solids (no solvents).

The manufacturers of WEST System epoxies -- a highly regarded brand among boatbuilders -- say this:
"Adding solvent is a quick, simple method of thinning epoxy, but unlike using heat to thin it, the strength and moisture resistance of the cured epoxy are drastically affected." <link>

WEST System tested acetone, lacquer thinner, and denatured alcohol, and concluded, "For a variety of reasons, fast-evaporating lacquer thinner appears to be more appropriate for thinning purposes than acetone or alcohol."

Bottom line from WEST System is:
"Adding 5% lacquer thinner to epoxy reduces the epoxy’s compression strength by 35%—a big hit in the mechanical properties of WEST SYSTEM epoxy (Figure 5). The addition of more than 5% solvent results in an excessively flexible cured material. Thinning epoxy with solvent causes enough loss of strength that we (and most other reputable epoxy formulators) cannot recommend using it as a structural adhesive."

System Three, another respected manufacturer of epoxy, gives this advice:
"For coating applications, an epoxy resin systems can be thinned with solvents such as lacquer thinner, or denatured alcohol for better brushability. In most cases, adding 1-3% solvent to a mixed batch of epoxy is all that's required. Never thin adhesives as the bond strength can be compromised."