TECHNET Archives

November 2007

TechNet@IPC.ORG

Options: Use Monospaced Font
Show Text Part by Default
Show All Mail Headers

Message: [<< First] [< Prev] [Next >] [Last >>]
Topic: [<< First] [< Prev] [Next >] [Last >>]
Author: [<< First] [< Prev] [Next >] [Last >>]

Print Reply
Subject:
From:
David Douthit <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, David Douthit <[log in to unmask]>
Date:
Mon, 19 Nov 2007 09:50:56 -0700
Content-Type:
text/plain
Parts/Attachments:
text/plain (209 lines)
Ben,

When you exceed the Tg for extended time periods the physical  
properties of the coating has transitioned from a "solid" glass like  
material to a "softer" rubber/sticky/paste and in extreme cases syrup  
like material.

I have always had questions about the phrase "Continuous Use  
Operating Range" when venturing above Tg. The primary concern is the  
end use environment and conditions encountered while above Tg at any  
time. For a more complete understanding  of coatings I strongly  
suggest you get a copy of the IPC Conformal Coating Handbook - IPC- 
HDBK-830.

David A.Douthit
Manager
LoCan LLC
On Nov 19, 2007, at 6:27 AM, Gumpert, Ben wrote:

> David,
>
> How does this fit in with the "operating range" given by the vendor?
>
> Take Humiseal 1B31 for example:
> 	Continuous Use Operating Range 		-65°C to +125°C
> 	Glass Transition Temperature (TMA)		 14°C
>
> I would not be exceeding the design limitations by baking, but it  
> would be difficult not to exceed the Tg.
>
> Ben
>
>
> -----Original Message-----
> From: David Douthit [mailto:[log in to unmask]]
> Sent: Monday, November 19, 2007 7:44 AM
> To: TechNet E-Mail Forum; Gumpert, Ben
> Subject: Re: [TN] Conformal coating Rework
>
> Ben,
>
> The short answer is yes!
>
> The longer version is that there are numerous issues when you  
> exceed the Tg of the coating material for extended periods.
> Among them;
> 1. contamination penetrating the coating
>
> 2. carbonizing/changes to the chemical/electrical properties (turning
> brown)
>
> 3. de-lamination weakening of the surface bonding
>
> 4. evaporation/flowing of the coating material (to thick/thin or  
> going where it is not wanted)
>
> In short you have exceeded the design limitations of the coating  
> material and may be forced to "re-qualify" the product after this  
> procedure.
>
> David A. Douthit
> Manager
> LoCan LLC
>
> --------------------------------
> On Nov 19, 2007, at 3:52 AM, Gumpert, Ben wrote:
>
>> Yes, that is the process I would use as well.
>> I have a BGA on a 63/37 HASL Polyimide board.
>> But I am not concerned about the board and what moisture it has
>> absorbed, the BGA is my main concern (MSD Level 4). It is expensive
>> enough that I don't want to throw it away, so I feel the need to bake
>> it prior to rework.
>>
>> But when I bake the board, the conformal coating turns brown - is  
>> this
>> a problem?
>>
>> Ben
>>
>> -----Original Message-----
>> From: TechNet [mailto:[log in to unmask]] On Behalf Of Rodney Miller
>> Sent: Thursday, November 15, 2007 4:00 PM
>> To: [log in to unmask]
>> Subject: [TN] Conformal coating Rework
>>
>> Per Ben Gumperts email.
>>
>>
>>
>> I'm not sure the logic on baking a Conformal coated PCB?  If the
>> coating is working or you have residually absorbed moisture, you are
>> creating a problem by baking a CC'ed PCBA in my opinion.  The barrier
>> of conformal coating Ureathane or otherwise should be easy to remove
>> and locally repair with localized Reflow system.  If you are totally
>> reflowing the PCBA, that is even larger problem on rework.
>>
>>
>>
>> I would remove the part, with hot air.
>>
>>
>>
>> Remove Conformal coating with appropriate solvent from the area of
>> repair.
>>
>>
>>
>> Rework/re-solder components
>>
>>
>>
>> Reapply Components with localized Reflow and/or HotAir system.
>>
>>
>>
>> There will be some aesthetic issues, but with proper solvents and
>> cleaning, you should not have issue with moisture in the PCBA more
>> than any other issue.
>>
>>
>>
>> Is this RoHS or 63/37 solder?
>>
>>
>>
>> How long have they been in Ambient conditions?
>>
>>
>>
>> What is the laminate?
>>
>>
>>
>> What is the plating?
>>
>>
>>
>> What technology is the components that are to be reworked?
>>
>>
>>
>> Just my couple of CNY..
>>
>>
>>
>> Rodney
>>
>>
>> ---------------------------------------------------
>> Technet Mail List provided as a service by IPC using LISTSERV 15.0 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
>> 847-615-7100 ext.2815
>> -----------------------------------------------------
>>
>> ---------------------------------------------------
>> Technet Mail List provided as a service by IPC using LISTSERV 15.0
>> 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 847-615-7100 ext.2815
>> -----------------------------------------------------
>
> ---------------------------------------------------
> Technet Mail List provided as a service by IPC using LISTSERV 15.0
> 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 847-615-7100 ext.2815
> -----------------------------------------------------

---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 15.0
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 847-615-7100 ext.2815
-----------------------------------------------------

ATOM RSS1 RSS2