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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1-847-597-2818 (Phone)
1-847-615-7105 (Fax)
1-847-615-7100 (Main)