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

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Screen Printing Adhesive

#30780

Screen Printing Adhesive | 30 September, 2004

Hi All

We have two boards that we produce which are chip on glue. For this we use KME BD12's which use air to dispense the glue dot on to the board. This is not ideal as the glue dot size differs as we go down the tube causing us quality problems. I therefore want to look at either screen printing glue onto the board or screen printing some conductive material onto the copper pads which will cure the pad to the part but at the same time still allow the board to go through the lead free wavesolder.

I know these materials are available but does anyone have any experience of using them.

Thanks

Terry (UK)

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Loz

#30781

Screen Printing Adhesive | 30 September, 2004

Screen printing glue is definitely easier and more repeatable than using dispense methods (my opinion). Depends a lot though on pcb design and component mix. Contact your stencil vendor and they will be able to suggest different apertures, such as lines or dots, all dependent on component mix. Stencil thickness increases to 8-10 thou. As for screening conductive material (soft solders?), why would you need this method? I'm not sure what the properties you mention are of this material, ie cure temperature etc. It seems that the glueing would suit your needs more. Also when glueing you will need to change your screen printer settings, dependent on your machine, your screen printer vendor should be able to advise on this matter. Hope this is of some help.

Loz

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#30788

Screen Printing Adhesive | 30 September, 2004

USING CONDUCTIVE EPOXY: Epoxies do not bond well to tin or tin alloy surfaces. * For components: a silver-palladium or gold end termination is recommended. * For substrates: gold over nickel should work well.

Remember epoxy is not hermetic, and oxygen can migrate to the interface, resulting in latent failures. [See, this goes back to the genesis of the whole lead-free thing. The Euro-greens thought it would be simple to replace metal solder with epoxy. Aux contraire. Now, we have what we have.]

PRINTING GLUE: Search the fine SMTnet Archives for background discussion.

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JB

#30791

Screen Printing Adhesive | 30 September, 2004

We used to screen print glue on some of our PCBS. And it does work well, you would probably need a new set of squeegess so you can use for glue only. As some one suggested before, find out what appertures would work with your product.

Screen printing glue can get messy though.

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dgjjr

#30797

Screen Printing Adhesive | 30 September, 2004

We have been screen printing adhesive for about 4 years. Works well but it does require my opertators to pay more attention to what they are doing than they would prefer. Keep your stencils really clean. Once that epoxy dries in an aperture, it is hard to remove.

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SMT in-printer dispensing

StikNPeel™ Rework Stencils