Hello Tim,

We have a customer (military) that had us bonding some larger parts to
the PCB using RTV silicone.  Then when the customer tried conformal
coating after they finished and tested - they had big concerns that the
coating would not adhere properly to the silicone RTV in the long run.
They eliminated the RTV in the next set we built.  They said there is a
compatibility problem with the type of conformal coating that was
specified (don't know what they were using).  You may want to contact
the coating company and see what they say about silicone based bonding
material and how it will react with the conformal coating.

Tom

Tim McQuay wrote:
>
> 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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