Hot melt glue or something else?

[jeremy]

Hi all,

Sometimes when I am modifying a PCB I need to use some sort of adhesive to stop any wires flexing on the solder joint. I have in the past used ultra cheap hot melt glue sticks with an ultra cheap 15W glue gun and I am finding that the glue is often not runny enough to seep down past wires and onto the PCB and solidifies frustratingly quickly (a 20-30 second drying time would be perfect, I feel like I'm getting 5 seconds at best).

Is there a better way to do this? Or am I just using the wrong/crappy equipment?

Thanks.

[DmitryL]

After applying a hot glue from your glue gun you can try give it a finishing touch with a hot air soldering station. Air temperature around 150 degrees C should be fine.
It will melt it.

[Frost]

I am finding that the glue is often not runny enough to seep down past wires

I use UV curing adhesives for this purposes.
To start the curing process I use a UV LED torch like dentists do.

[ConKbot]

It sounds like using a high temperature glue gun instead of a low temp glue gun (and different sticks as appropriate) would help the glue flow better before it sets. Mind your fingers as IIRC high temp glue guns and dispense at ~350F. 

You could also use acid free silicone (methoxy cure) or 5 minute epoxy.  Do some testing to make sure your adhesive of choice sticks to the solder mask, as its a surprisingly resilient and hard to bond to at times, surface.

[jeremy]

I use UV curing adhesives for this purposes.
To start the curing process I use a UV LED torch like dentists do.

This is quite interesting actually, can you recommend any product codes or Loctite/3M numbers?

[HSPalm]

There exists both low temp and high temp glue guns, do you know which type you have? I know parents ask for the low temp type in hobby stores because its more safe for kids.

[robrenz]

Gel type super glues with a dabbed with super glue activator sprayed onto a Qtip works well and is much cheaper yet less convenient than the UV approach.

[luky315]

Hot Glue is hygroscopic. Don't use it near precision and/or stable circuits. I had a lot of problems with it.

[HSPalm]

Yup that's true. I know hot glue is used for tuning certain types of circular polarized antennas which can not be trimmed in length.

[Frost]

Can you recommend any product codes or Loctite/3M numbers?

Yes, but I can't recommend anything you can buy in Australia
I use Bondic, it's a product you get here at a certain hardware store.

It's not really cheap and I am sure from Henkel or 3M you
will get more value for money, same thing with the super glue
you can buy at the hardware stores.
But I only need small amounts to retain wires or SMD chips
for hand soldering.

But one tube last for years, instead of the superglue
which is always dried out when I need it

[nctnico]

I recommend using hot melt glue. It sticks well to other plastics yet it is relatively easy to remove without damage.

[vikpc]

hi! i use this for fixing wires and some fast components fixing... it starts in 5-10sec... and not have power wires! very useful.

[Rufus]

Hot Glue is hygroscopic. Don't use it near precision and/or stable circuits. I had a lot of problems with it.

So I clip my insulation tester on a bit of hot melt glue stick which has been kicking around at the back of my bench for at least a couple of years - didn't even clean the surface. The gap between the croc clips was less than 10mm.

The tester reads overload, greater than 1T ohm at 5kV.

[SeanB]

Cook it and then leave in a humid place for a month then try again. Good luck getting more than 10M out of it.

[pickle9000]

If you have a pcb preheater use that before applying the hot glue.

If you want it be be ultra long lasting use a clear 100% silicone, takes overnight to set up but bonds really well to surfaces. To make the silicone more rigid I use place a small square of clear polycarbonate on the surface.

[Rufus]

Cook it and then leave in a humid place for a month then try again. Good luck getting more than 10M out of it.

I left it in a submerged place for more than 7 years and get much more than 10M out of it :-

https://www.eevblog.com/forum/projects/(tips)-strengthen-the-diyself-made-hook-probe%27s-join-using-hot-glue-gun/msg67507/#msg67507

The lid has rusted and most of the water has now evaporated. The resistor today still measures 10.15M.

[aargee]

Funny, when i saw the title I instantly thought "invariably something else".
Hot melt glue doesn't like Australian summer heat (I guess not a big problem for this application).
The glue sticks are not of a consistent compound depending where you source it.
I have had HV problems with Hot melt where the glues involved created internal HV carbon pathways, breaking down.

Great for crafts and the "gaffa tape / fencing wire / baling twine" type MacGyver fix.

Most wiring fix in lace type adhesives I've seen are a Cyanoacrylate with filler.

[Rufus]

The glue sticks are not of a consistent compound depending where you source it.

Part of the problem is there are many types of hot melt glue. My experience is with cheap standard temperature Polyolefin Copolymer sticks, white/translucent, feel slightly waxy.

[BravoV]

I left it in a submerged place for more than 7 years and get much more than 10M out of it :-

https://www.eevblog.com/forum/projects/(tips)-strengthen-the-diyself-made-hook-probe%27s-join-using-hot-glue-gun/msg67507/#msg67507

The lid has rusted and most of the water has now evaporated. The resistor today still measures 10.15M.

Ah.. just remembered that old thread.

Rufus, take a photo of that jar please, I guess it looks disgusting ... interesting. 

[Rufus]

Rufus, take a photo of that jar please, I guess it looks disgusting ... interesting. 

First a picture of the insulation tester clips and bit of hot melt stick which measured > 1T ohm @ 5kV.

Then top of the jar, the resistor in its hot melt coating, and the resistance measured across the wires.

The jar started about half full of water with a couple of tablespoons of salt added, only in the last year or so did the water level start dropping significantly. The salt water does something to the hot melt, early on there were some debris in the water like the hot melt was shedding thin skin.

[BravoV]

7 years in salt water with constant exposure of uv light from the sun + daily thermal cycle, quite impressive imo.

Thanks Rufus , that post is now bookmarked for future reference. 

[JBeale]

Hot Glue is hygroscopic. Don't use it near precision and/or stable circuits. I had a lot of problems with it.

That may be specific only to some kinds of hot-melt glue.

http://en.wikipedia.org/wiki/Hot-melt_adhesive lists 12 broad categories of base materials (EVA copolymers, Polyamides, Polyesters, Polyurethanes, Styrene copolymers, Polycarbonates, Fluoropolymers etc.) and  10 categories of additives.  In some cases hygroscopic materials are intentionally added to allow microwave heating.

[scientist]

Use 20-minute epoxy and mix it correctly so it is stable, yet flexible. Hot glue will always disappoint.

[LukeW]

I'm not surprised there are HV issues with the hot melt glue. But I wouldn't use it for HV! It's great for general purpose applications at low voltages where it's not expected to fly men to the moon, and you want something cheap and convenient where using specialist glues or sealants is not financially justified though

[sacherjj]

If you want it be be ultra long lasting use a clear 100% silicone, takes overnight to set up but bonds really well to surfaces. To make the silicone more rigid I use place a small square of clear polycarbonate on the surface.

Make sure the silicon won't be corrosive.  It needs to be neutral cure.  Mose RTV Silicone will release acids.  Make sure to look for neutral cure.

Hot melt is only OK if you need it to last under a year.  But you can use dabs of hot melt to hold a component so silicone can cure.  Good silicone is a 20+ year solution.