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SMT electronics assembly manufacturing forum.


High Temp (96/4) adhesive cure time/temp

#5304

High Temp (96/4) adhesive cure time/temp | 21 February, 2001

Could anyone please give me some insight on the time/temperature requirements for curing SMT adhesive used for a high temperature (96/4 solder) application in a bake oven, rather than using reflow? I understand that it would probably vary from epoxy manufacturer to manufacturer, but I'm looking for a rule of thumb. Thanks for any input you might have.

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#5306

High Temp (96/4) adhesive cure time/temp | 21 February, 2001

You're right, manufacturers time/temps will vary. A single manufacturer will have a host of materials with different cure schedules. We currently use 2 epoxies that cure in 2 - 3 minutes at 150�C. One will also cure in 5 minutes at 125�C. Talk to epoxy manufacturers and I'm sure they can come up with a cure schedule to meet your requirements.

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#5314

High Temp (96/4) adhesive cure time/temp | 21 February, 2001

I�m unclear about the intent of your question, but I�ll take a pass at it regardless.

I second the previous poster's commets. [Ya, that's the ticket.] Most chip attach adhesives should not be cured at typical reflow profile temperatures. Check your supplier use instructions. For example, you�ll find a cure cycle of 145-150�C for 4-5 minutes for Loctite 3609 / Epibond 7275 / Epibond 7275-1.

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#5316

High Temp (96/4) adhesive cure time/temp | 21 February, 2001

I appreciate both of your responses. I spoke with a tech rep at a distributor of the Loctite 3609 and asked him if this adhesive can be cured using a bake oven (Blue M, Despatch, etc.), rather than convection/IR. He stated that he's never heard of anyone using a bake oven for this application, only a reflow oven with a much lower profile, i.e. 1 degree C/sec and max temp at 150 degrees C for 45 seconds. Dave, does this clear up the intent of my question at all for you? What I'm trying NOT to do is having to purchase a reflow oven when 99% of our business uses an epoxy application (Burn-in boards with passives on solder side.

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#5318

High Temp (96/4) adhesive cure time/temp | 21 February, 2001

Gary: It doesn't matter what you use to cure your glue.

SMA adhesives are thermosets. This means they become hard on cure and this is not reversible. A couple of things go on with SMA adhesives when you heat them. * Their rheology is temperature dependent, so as you warm them the viscosity goes down. * As you warm them they cure so the viscosity goes up [to infinitely high]

We use an ancient Vitronics 722 [or something like that] 12" wide IR oven that's older than dirt. We tried to sell it when we bought our new oven, but everyone just snickered.

After buyin' the new oven, we were doing what that dopey rep talked about ... flippin' between high and low temperature profiles [loosin' time, makin' the meter spin, and all that] ... and one day one of the guys on the line asked if he could use the old oven to cure glue. Well, duh!!!

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#5324

High Temp (96/4) adhesive cure time/temp | 22 February, 2001

An adhesive, is an adhesive, is an adhesive. Yes most will thin when exposed to elevated temperature, but that's only for a short time. As cross-linking starts, viscosity increases. Having made countless numbers of adhesively bonded samples in the aerospace industry, an oven will work.

My experience with Blue M's is that many are programmable. If so you can program what ever cure schedule that you want (including a ramp up and/or down). If you are placing components on the board and transferring them to an oven, my concern would be that the components might shift. People do bump into things ya know. In line cure ovens minimize any movement of the components prior to cure.

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Travis Slaughter

#5329

High Temp (96/4) adhesive cure time/temp | 22 February, 2001

I used a Blue M batch oven quite a bit to cure in works great. All you have to do is get the board up to cure temperature, 150C normally and your all set. It will probably be in there longer than the time required but at that low temperature it shouldn�t hurt anything.

PS: Dave F I used Vitronics 310 and 318 ovens to cure for a long time they are likely still in use.

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#5340

High Temp (96/4) adhesive cure time/temp | 22 February, 2001

Travis: I just checked.

You're correct. It's a SMD-310, circa 1985 with a 12" wide mesh belt and a screamin' three zones of solder meltin' fury.

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