Best glue for cracked circuit board?

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.

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.

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

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.

It looks like paxolin to me.

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

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.

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.

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!

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."

Thanks Dan and Gary, lots of thinking to do.

Current thought is to glue (with something) a thin bit of plastic on the top of the part, with holes for the centre screw and the rivets and then trim to shape once dry.

I've used some processed film base as a thin plastic support for repairs in the past.

Mike

Thanks Mike, great idea!

Let's see how this goes! Original cracked paxolin board reinforced with a layer of film on top.

The pivot screw has a shoulder allowing the screw to be tightened whilst still allowing the paxolin board to rotate, there is also a spacing washer below to avoid squashing the metal contact fingers riveted to the bottom of the board.

So a large hole needs to left in the film as well as two smaller holes either side to clear the rivets. A paper punch was the right size for the centre hole and a 1.5mm punch from a leather working kit took care of the two smaller holes for the rivets.

A couple of small recesses were drilled in a bit of wood to give clearance for the rivets and the film taped to the wood to hold it in place. I made a bit of a mistake here as I should have put a bit of cling film down first so to avoid the film becoming stuck to the wood by the glue seeping through the holes, but I did manage to unstick the switch from the wood once everything was set by using a thin knife. A thin smear of Araldite was spread over the crack on the paxolin board and also on the film, using a hair-dryer to warm everything to make the Araldite less viscous.

Then the paxolin board was placed on top and clamped down using a couple of cocktail sticks and left to dry. Before clamping, a bit of cling film was pushed in between the board and the two small contact fingers (situated between the two cocktail sticks) in case any glue made its way under the fingers and stuck them to the paxolin board.

The following day, the paxolin board, now with a film backing, was unclamped, the excess film removed with a sharp knife, and the switch assembled. All good so far, battery check fine and meter working as expected in both auto and manual modes. On to the next issue with this camera!

Looks great!

Thanks, hopefully it will keep holding up, time will tell.

Great job. I hope it holds up.

When you opened this thread, my first thought was to suggest getting a similar material, trace the part, and use files to shape it - then transfer the metal piece (it looks simple enough, nothing seems to be "printed" on the board).

On the other hand, I can really appreciate repairing the original part, for many reasons. There is something very satisfying about not swapping parts.

Can someone explain Araldite to a US person? Is it a clear epoxy? Sort of standasrd issue hardware store variety? After mixing it is a bit runny, would flow out to a 1-2mm thick blob?

Dan Daniel said:

Can someone explain Araldite to a US person? Is it a clear epoxy? Sort of standasrd issue hardware store variety? After mixing it is a bit runny, would flow out to a 1-2mm thick blob?

Click to expand...

Looking at their <webpage>, Araldite seems to be a brand name for a family of epoxy-based adhesives.

One of their company webpages says,
"Huntsman Advanced Materials (formerly part of Ciba-Geigy) revolutionised the world of adhesives in the 1940s when they launched the new epoxy technology in Switzerland under the Araldite® brand name."

So far, I have not found any evidence that Araldite brand epoxy offers any great benefit over many similar products made by competing brands. Epoxy companies like WEST Systems publish physical data for specifications like tensile strength, compression strength, hardness, viscosity, etc. for each of their resins. But if Araldite publishes any such performance data or specifications for their products, I haven't found it.

Yes, it's a two part expoxy adhesive, probably similar to many others as Gary says. Farnell have a specification sheet (dated 2015) on their site here. I would say it’s probably standard hardware store issue. It's quite viscous when mixed, but thins up if heated.

For me Araldite was the first epoxy resin adhesive I saw. It seemed to be a miracle adhesive.
If not advertised as, it could be used to build up worn cams on light machinery.

To me the word Araldite is used like BIC pens, and Hoover vacuum cleaners.
Any cheap ball point pen is a BIC. Just like any vacuum cleaner is a Hoover.

Araldite is tried and time tested, so that is the name I go for.

Until I read this thread, I never heard of Araldite.

In the USA, brands like JB Weld, Loctite, Devcon, Permatex, and Gorilla Glue offer epoxy adhesives in twin-syringe packaging similar to Araldite.

Generally speaking, I think the 5-minute versions tend to be not as strong or waterproof compared to slower setting formulations. Although it may not matter for many repairs like @Flighter's -- I would choose the regular "overnight cure" versions if your repair will be subject to higher stress or prolonged wet conditions.

Compared to the twin-syringe packaging, it is much more economical to buy 2-part epoxy in larger packaging. For example, the JB Weld brand 5-minute epoxy is about $2.40 per ounce if bought as an 8-ounce kit, but is over $7.00 per ounce in the 25mL twin-syringe packaging.

For the American market, I prefer something like this for all-purpose bonding of various materials:



The twin-syringe dispenser is not at all necessary. Just lay out a bead of resin, and then lay out a bead of hardener next to it, and mix them up.

Truzi said:

Great job. I hope it holds up.

When you opened this thread, my first thought was to suggest getting a similar material, trace the part, and use files to shape it - then transfer the metal piece (it looks simple enough, nothing seems to be "printed" on the board).

On the other hand, I can really appreciate repairing the original part, for many reasons. There is something very satisfying about not swapping parts.

Click to expand...

Thanks Truzi.

Yes, that's my plan B if gluing doesn’t work. As you say, there’s nothing printed, the paxolin just serves as a mount for the wiper contacts and a mechanical link to the mode switch on the top cover and the link on the underside which changes the meter display in the view finder between the manual mode (+ and -) and aperture priority (all shutter speeds with needle showing selected speed).

I went with the regular overnight cure version of Araldite as it gave a much longer working time to position the pieces, as I knew that heating would reduce the working time but I wanted to get it to a thinner consistency to penetrate the crack on the board ehilst having plenty of time to get everything positing and clamped up. There's a choice between a twin-tube dispenser and the one I went for, two separate tubes, just squeeze out equal volumes and mix.

Like Bob, Araldite was the first epoxy adhesive I knew as my dad, a mechanical engineer with a hobby of working on cars, always had some around the garage.

I suggest shellac, a 30# cut as both an electrical insulator and structural support, which can easily be removed by way of alcohol.

Some Japanese Kozo or Hanoi paper, can be used to reenforce the repair but we‘re talking about making a match sized paper patch, soaked in shellac.

Its just as easy to remove as the shellac.

Thanks Eli, I never thought of shellac for this, I've used it before for gluing new ink sacs in fountain pens. I'll need to investigate the Kozo and Hanoi paper.