Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Is more epoxy better?

Charlie

#6636

Is more epoxy better? | 18 May, 2001

When it comes to how much epoxy [aka. "glue"] to dispense to hold a IC or any part with significant mass, on the bottom of a board for wave soldering, is more better? The way I see it, one good dot should be holding such a part on the PCB. If not, there is moisture or contamination involved. What do you guys think?

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Michael Parker

#6638

Is more epoxy better? | 18 May, 2001

Good ol' Yankee engineering always says "More is better"

You have got to be careful that with more epoxy volume you run the risk of the epoxy merging with solder paste if you are using a glue and paste process. In addition, if the epoxy can spread out and cover the pads, then wave solder cannot create a good fillet.

Less is more. Just enough is better.

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#6649

Is more epoxy better? | 21 May, 2001

Continuing the line of Michael's, the previous poster, comments ...

The more Krispy Kremes, the better. Yeth!!! The more beer, the better. Yeth!!! The more epoxy, the better. Uh, I don think so!!!

We look at this from a papa bear, mama bear, baby bear stand-point [http://www.on-net.net/~tdickins/goldi.html].

PAPA: Well if you do too much "more is better", you end-up with glue on pads and less than the amount of solder that you�d kind like. And maybe if you dab on too much of that stuff, it just might make it tougher to cure.

MAMA: Certainly if you dab on too little, when you jamb the component into your glob of glue it will not schmush-out enough to have sufficient contact area and will not hold the component in place properly. Then the floor sweeper people be complaining about how much additional work they have and on and on.

BABY: Now if you apply just the right amount, �

Continuing, as far as the number [and location] of epoxy dots for a component is [are] concerned, that depends on the epoxy and the component. * We UV cure epoxy multiple dots on the edges of components. * Generally, we use a single dot for heat cure epoxies when gluing small components. * Even when using heat cures, we use multi-dot patterns for larger components.

Other points are: * IPC-7525, Stencil Design Guidelines makes such a feeble attempt at aperture design for printed epoxy and promises to address the issue some other time that together become no reason to buy the document for these purposes. * Trade journals seem to be incessantly chattering about such things in an on-going war of attrition between the dispenser and the printer equipment manufacturing firms. Look at the May 2001 "SMT" magazine an example.

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mike mullan

#6733

Is more epoxy better? | 30 May, 2001

It may be the case (if you are using stencils to apply the epoxy) that you will have to indeed use a stepped stencil to appply the epoxy at a greater height.

Not being an engineer i am not completely clear with the involvements of stencil design - but having seen the problem being fixed by the stepped stencil (with a narrower aperture to reduce the amount of epoxy placed) i thought that this might interest you.

Mike

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mike mullan

#6734

Is more epoxy better? | 30 May, 2001

It may be the case (if you are using stencils to apply the epoxy) that you will have to indeed use a stepped stencil to appply the epoxy at a greater height.

Not being an engineer i am not completely clear with the involvements of stencil design - but having seen the problem being fixed by the stepped stencil (with a narrower aperture to reduce the amount of epoxy placed) i thought that this might interest you.

Mike

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