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Epoxy application

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#52599

Epoxy application | 20 November, 2007

Hello, I would like to ask for opinion on an epoxy application. We apply RTV to bond and secure 2 electronic devices on a PCB.

But after noticing the RTV bond breaking off during vibration test, our customer has specs in a 5min 2-part epoxy (made by http://www.devcon.com/techinfo/5_MINUTE_FR.pdf) to replace the RTV. The problem is that the Devcon epoxy is fast cure, requries 2 part mixing, and carries a strong, irritating odor. I would like to move away from using Devcon and expect that there must be more process friendly epoxy for such application.

The 2 materials to be joined were a flat ferrite inductor and round capacitor having a PVC sleeve. Due to positioning of the 2 devices there is generally a ~0.25" gap between them for the epoxy to fill. The epoxy bead deposit is about .75" long x 0.5" wide. (see following link to the assembly http://members.shaw.ca/ppwlee4/Epoxy_appl.JPG)

I am looking for recommendation of a suitable epoxy to allow: - 5-10 min working life before it starts curing - process friendly (smell, preferrable no pre-mix) - good adhesion to the component/PCB surfaces.

Any suggestion is appreciated. Thanks.

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#52600

Epoxy application | 20 November, 2007

Peter: The above link to the the picture of the assembly is broken.

Comments are: * Yes, RTV is completely useless for applications like you describe. Epoxy is a much better choice. * Dave G, in an archived thread on SMTnet, talks about using 3M Jetmelt 3748 for a similar application. It's a hotmelt. Look it up. * Consider contacting applications type at epoxy suppliers [eg, Master Bond, Loctite, etc] for their recommendations? * Would a uV curable [eg, Dymax, Epoxies, etc] work. With these, you need to keep the bondline thickness below 0.125" AND you don't apply it in areas that are 100% shadowed from the light. * You might need two materials. Ferrites are often attached with an activator cured acrylic adhesive (eg, Dymax, Loctite or Permabond). Epoxy and hotmelts are good shock mounts.

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#52604

Epoxy application | 21 November, 2007

#52672

Epoxy application | 27 November, 2007

I would agree with the above. Epoxy is the way to go. You can have it formulated in different thicknesses and cure times, but you need to watch out for the exothermic heat from the curing.

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#52684

Epoxy application | 28 November, 2007

DevGru: Questions are: * What steps do you recommend taking to "watch out for the exothermic heat from the curing?" * What are typical temperatures for exothermic heat from the curing? * What is the duration of such temperatures? * Do epoxy suppliers expect customers to specify the exothermic heat from the curing? If so, how does variances from the exothermic heat from the curing of the standard product affect price?

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#52690

Epoxy application | 28 November, 2007

We use TraCon's TraBond 2112 for staking applications where larger gaps are involved. It is formulated for PCB staking applications. The material is very low sag and high viscosity. It's 2part and comes in handy bi-paks. Work life is 20-30min.

Strength? - Don't question it. We've had numerous customers perform shock and vibe testing with good results.

The only drawback is that there is a largish min qty (25-50 2gram packs). We use a bunch of it so it's not a problem for us.

Cheers.

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#52706

Epoxy application | 29 November, 2007

Henkel Loctite makes a hot melt just for this. Do a web search on Loctite Hot Melt and you can see for yourself. Material comes in a variety of ways - we use the 10 inch sticks and their glue guns specially made for the material. Works well, is fast to apply, no smell, dries within seconds. You can't go wrong.

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#52725

Epoxy application | 30 November, 2007

The hot melt is prob the only way to go for that size gap. If you could decrease that gap I would suggest using 3M Scotchweld DP100FR. Check it out. We use the duo pak cartridges and mix nozzles with the gun. Very simple use and works great in our ESS testing. Its also flame resistant and meets UL-94-VO standard.....

JD

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#52734

Epoxy application | 1 December, 2007

Sam emailed us: "Dave: Many UV cure materials have secondary heat cure or air cure properties."

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