Dow DC3145 is made specifically for the electronics industry. We've been using it here since my first stint starting in 1981. BEWARE of imitations...dear price to be paid if you don't get the right one.
Our service dept prefers we use RTV over epoxy because of service requirements. Some assemblies are becoming inexpensive enough to no longer warrant the need for service or repair, so epoxy would be a better way to go; costs more for a tech to troubleshoot that to toss assy away and get a new one.
And yes, we see the same problem with acrylic and urethane coatings not wanting to stick to RTV. Some acrylics seem to be worse than urethane. But we seem to get a decent seal around the periphery of the RTV/component/pcb joint for this not to be a serious problem. However, I can see this being a major issue with moisture sensitive circuits/designs. We also allow the RTV to cure a minimum of 24 hours before coating.
Though, like Brian said (along with the other esteemed members who contribute to this great forvm), epoxy is really a wise choice. Anybody use a Loc-tite type of product for staking? Just curious...
Have a great one!
Roger M. Stoops, CID+
Trimble Navigation Ltd., Dayton, OH, USA
Ph: +01 937.245.5288
Fax: +01 937.233.7511
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Brian Ellis
Sent: Thursday, February 26, 2004 11:12 AM
To: [log in to unmask]
Subject: Re: [TN] Conformal coat over RTV?
I was assuming, in my early response that no one, in their right mind,
would even dream of using the RTVs based on an acetic acid reaction on
an electronics assembly. If the RTV smells sharp or vinegary before
curing, you are already in DEEP trouble.
Brian
Ofer Cohen wrote:
> Most RTV compounds will out gas mild acid along the life cycle. Closing is under coating may cause the acid to attack the RTV near components and PCB.
>
> Ofer Cohen
> Manager
> Quality Assurance, Reliability and Production Technologies
> Seabridge Ltd. - A Siemens Company
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]]On Behalf Of David Douthit
> Sent: Thursday, February 26, 2004 17:57
> To: [log in to unmask]
> Subject: Re: [TN] Conformal coat over RTV?
>
>
> Mark,
>
> DON'T!!!
>
> The fact that the components are "sensitive" combined with the fact that
> the coating will not bond properly results in an environmental exposure.
>
> Why RTV staking, cost? Use epoxy!
>
> Trying to save money no matter how much it costs is very expensive!
>
> David A. Douthit
> Manager
> LoCan LLC
>
> Mark Charlton wrote:
>
>
>>My learned and esteemed colleagues,
>>
>>One of our customers has requested that we conformal coat over a DOW 3145
>>RTV adhesive used to stake some sensitive components. The specified coating
>>material is MS470-N, a urethane product.
>>
>>Is this a standard practice (to coat over RTV)? We have always conformal
>>coated the PCA and then staked the components using the RTV. Our CC vendor
>>isn't too pleased with this request.
>>
>>Mark Charlton
>>
>>---------------------------------------------------
>>Technet Mail List provided as a service by IPC using LISTSERV 1.8e
>>To unsubscribe, send a message to [log in to unmask] with following text in
>>the BODY (NOT the subject field): SIGNOFF Technet
>>To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL)
>>To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest
>>Search the archives of previous posts at: http://listserv.ipc.org/archives
>>Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315
>>-----------------------------------------------------
>>
>>
>>
>>
>
>
> ---------------------------------------------------
> Technet Mail List provided as a service by IPC using LISTSERV 1.8e
> To unsubscribe, send a message to [log in to unmask] with following text in
> the BODY (NOT the subject field): SIGNOFF Technet
> To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL)
> To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest
> Search the archives of previous posts at: http://listserv.ipc.org/archives
> Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315
> -----------------------------------------------------
>
> ---------------------------------------------------
> Technet Mail List provided as a service by IPC using LISTSERV 1.8e
> To unsubscribe, send a message to [log in to unmask] with following text in
> the BODY (NOT the subject field): SIGNOFF Technet
> To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL)
> To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest
> Search the archives of previous posts at: http://listserv.ipc.org/archives
> Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315
> -----------------------------------------------------
>
>
---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 1.8e
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL)
To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest
Search the archives of previous posts at: http://listserv.ipc.org/archives
Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315
-----------------------------------------------------
---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 1.8e
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL)
To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest
Search the archives of previous posts at: http://listserv.ipc.org/archives
Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315
-----------------------------------------------------
|
