Hey Tim,

As I recently learned from good ole Graham . . .
Silicone doesn't like to stick to anything including other silicone
products.
I ran into the same dilemma you are facing and changed both the adhesive to
an epoxy (DP-125 EG) and the conformal coating to polyurethane.

Most silicone adhesives recommend using a primer (SS 4004 for instance) to
add adhesion to the pcb surface.

And as always, all disclaimers apply - this is not an implied endorsement of
any product or service.

Hans

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Hans M. Hinners
Electronics Engineer (who used to do Fab)
Warner Robins - Air Logistics Center (WR-ALC/LUGE)
226 Cochran Street
Robins AFB GA 31098-1622

mailto:[log in to unmask]

Com: (478) 926 - 5224
Fax:   (478) 926 - 4911
DSN Prefix: 468


-----Original Message-----
From: Tim McQuay [mailto:[log in to unmask]]
Sent: Thursday, May 23, 2002 1:45 PM
To: [log in to unmask]
Subject: [TN] Conformal coating / gluing


Hi Folks:
We have a debate regarding sequence of operations when we glue down
components and apply conformal coating to the same board. The IPC-A-610C
does not cover this and I have not been able to locate any other info.
Basicly we want to know, do we glue first or do we coat first. Can someone
please tell us if the bond between silicone glue and conformal coating is as
strong as between silicone glue and PCB uncoated surface. We are concerned
that heavy components, such as the large caps on some of our boards, would
not be well supported if bonding is done after conformal coating.
We have our own bias but we wanted to hear an outside opinion and/or see a
standard on the topic. The adhesive and coating we use are listed below.
        3-1744 (DOW), SILICONE ADHESIVE - for staking big components
        KE3421 (SHIN-ETSU), SLCN BRD COAT - conformal board coating

Thanks
Tim McQuay
Training Coordinator
Vansco Electronics
Fax: 204-474-1674
e-mail: [log in to unmask]

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