John,
It appears defining distance vs. percentage is winning the "e-mail barrage"
on this topic. It's good to see the number of responses generated by such a
change request. My I suggest, once you have compiled all responses and
taken all into consideration, that you send out another proposal before
sending out for vote?
Best regards,
Tom
John Perry
<[log in to unmask]
G> To
Sent by: [log in to unmask]
IPC-600-6012 cc
<IPC-600-6012@ipc
.org> Subject
[IPC-600-6012] Proposed IPC-6012B
Change for SnPb in SMOBC
04/19/2005 09:05
AM
Please respond to
"(Combined Forum
of D-33a and
7-31a
Subcommittees)"
<IPC-600-6012@IPC
.ORG>
Colleagues,
The IPC D-33a Rigid Board Performance Task Group is beginning the
development of an Amendment 1 to IPC-6012 Revision B. Relative to this is
a request to modify and append text in section 3.5.4.7, Final Finish
Coverage (Areas not to be soldered).
Background on change request:
A printed board was found to have small amounts of Tin Lead under the
solder mask with reflow/SMOBC finish. The part has been fabricated using
the selective solder strip process. The customer rejected the parts for
small amounts of tin lead found on bare copper and under the solder mask,
claiming with Tin Lead, the part no longer was Solder Mask over Bare
Copper. There is currently no IPC specification that prohibits such Tin
Lead on the bare copper. However, at some point it becomes a workmanship
issue per IPC 6012B paragraph 3.3.9.
Rationale for change request:
This new accept/reject criteria provides a check and balance for the tin
lead strip process (i.e., the process is not capable of absolute ZERO tin
lead as there is always trace amounts on some circuits) and at the same
time we don't want to be throwing away printed boards that are functionally
fine.
Proposed Change within 3.5.4.7 of IPC-6012B:
3.5.4.7 Final Finish Coverage
Final finish shall meet the solderability requirements of J-STD-003.
3.5.4.7.1 Exposed Copper (Areas not to be soldered) Exposed copper on areas
not to be soldered is permitted on 1% of the conductor surfaces for Class 3
and 5% of the conductor surfaces for Class 1 and Class 2. Coverage does
not apply to vertical conductor edges.
3.5.4.7.2 Tin-Lead under SMOBC
Tin or Tin Lead under SMOBC on areas not to be soldered is permitted on 1%
of the conductor surfaces for Class 3 and 5% of the conductor surfaces for
Class 1 and 2.
If you approve the proposed change without comment, please send your
approval, by May 3rd, to [log in to unmask] If there is a need to comment on
and discuss this within the task group, please respond through this e-mail
forum.
Thanks,
John Perry
Technical Project Manager
IPC
3000 Lakeside Drive # 309S
Bannockburn, IL 60015
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