I think the IPC-T-50 committee needs to add:
SMENIG: Solder mask over ENIG
SMImAg: Solder mask over immersion silver
SMImSn: Solder mask over immersion tin
Although on that last one, perhaps it should be SMOITN - solder mask over
immersion tin. I envision a Stooge-like pronunciation. Think of where we
could go with that. Smoitenly.....
Doug Pauls
From: "Wenger, George M." <[log in to unmask]>
To: <[log in to unmask]>
Date: 08/09/2012 05:55 PM
Subject: Re: [TN] SMOBC process
Sent by: TechNet <[log in to unmask]>
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.
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