TECHNET Archives

August 2012

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:
"Wenger, George M." <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Wenger, George M.
Date:
Thu, 9 Aug 2012 17:53:57 -0500
Content-Type:
text/plain
Parts/Attachments:
text/plain (75 lines)
Richard,

I think Rudy's email is absolutely correct.  SMOBC means Solder Mask Over Bare Copper.  This is a process used by many PCB fabricators.  They make SMOBC boards and can then put the final surface finish on the boards (e.g., HASL, ImAg, ImSn, ENIG, etc.)

I do know of at least one fabricator that does ENIG prior to solder mask.  One problem with doing this is that solder mask doesn't stick to gold as well as it does to copper.

Regards,
George
George M. Wenger
Senior Principal Reliability / FMA Engineer
Andrew Corporation - Wireless Network Solutions
40 Technology Drive, Warren, NJ 07059
(908) 546-4531 Office (732) 309-8964 Mobile
E-mail: [log in to unmask]

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D.
Sent: Thursday, August 09, 2012 6:43 PM
To: [log in to unmask]
Subject: Re: [TN] SMOBC process

Not exactly, Rudy. While SMOBC means no solder as you stated, Gerald said if there IS solder under the mask (non-SMOBC), the mask will separate from the traces when the CCA goes through reflow and the solder melts.

And to answer Gerald's question, gold plating on true ENIG (as defined per IPC 4552) will not melt under solder mask during reflow. Gold does not actually "melt" during soldering operations, the molten tin/lead in the solder will dissolve some of the gold into the SJ, but the gold never "melts". Same is true for nickel, copper, silver, etc.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of R Sedlak
Sent: Thursday, August 09, 2012 3:51 PM
To: [log in to unmask]
Subject: Re: [TN] SMOBC process

Gerald:
I respond partly because your message is confusing, but then I am easily confused these days.
SMOBC means Solder mask over bare Copper, so there should be nothing under the solder mask but Copper, no solder, ENIG, etc.  Your message implies that the solder under the mask causes problems.
My naive mind suspects that if you are getting mask lift, it may be due to moisture turning to steam, and the HASL treatment serves to minimize the contained moisture.

My 2.5 cents.
Rudy Sedlak
RD Chemical Company

--- On Thu, 8/9/12, Gerald Bogert <[log in to unmask]> wrote:

From: Gerald Bogert <[log in to unmask]>
Subject: [TN] SMOBC process
To: [log in to unmask]
Date: Thursday, August 9, 2012, 6:57 AM

August 9, 2012

 

Some of our OEMs manufacture PWBs using the HASL process and they use solder mask over bare copper (SMOBC) to prevent re-melting of the tin/lead from the traces during subsequent assembly level soldering operations.  If SMOBC is not used, the re-melting of the solder causes blisters under the solder mask coating which can result in peeling or flaking of some of the solder mask from the traces.

 

We have one OEM who will be manufacturing an ENIG board with solder mask.  My question is with this finish, will the gold melt during assembly soldering to cause the same issue as when using HASL?  Also, does anybody use SMOBC over ENIG?  My understanding that it can be done but the results are not cosmetically appealing. 


______________________________________________________________________
This email has been scanned by the Symantec Email Security.cloud service.
For more information please contact helpdesk at x2960 or [log in to unmask] ______________________________________________________________________

______________________________________________________________________
This email has been scanned by the Symantec Email Security.cloud service.
For more information please contact helpdesk at x2960 or [log in to unmask] ______________________________________________________________________

______________________________________________________________________
This email has been scanned by the Symantec Email Security.cloud service.
For more information please contact helpdesk at x2960 or [log in to unmask] ______________________________________________________________________

______________________________________________________________________
This email has been scanned by the Symantec Email Security.cloud service.
For more information please contact helpdesk at x2960 or [log in to unmask] 
______________________________________________________________________

ATOM RSS1 RSS2