Randy,
Good question. For us high reliability is minimum 20 years of field
life. We could design a high reliability board with selective solder
strip/reflow processing by having only long trace lengths between
passives/BGA pads and their escape vias, but the board would probably
not operate competitively at higher frequencies.
In this case we would like both Class 2 and Class 3 IPC requirements to
ensure high reliability, but with Class 3 having a tighter requirement
allowing higher performance design rules to be used (short and
solder-free trace lengths to escape vias).
Regards,
Karl Sauter
Reed, Randy wrote:
> Karl,
>
> For clarification purposes, What is Sun's definition of high reliability
> boards? Class 2 or Class 3.
>
> Regards,
>
> Randy Reed
> Merix Corporation
>
> -----Original Message-----
> From: IPC-600-6012 [mailto:[log in to unmask]] On Behalf Of Karl Sauter
> Sent: Thursday, April 21, 2005 9:27 AM
> To: [log in to unmask]
> Subject: Re: [IPC-600-6012] Proposed IPC-6012B Change for SnPb in SMOBC
>
> I agree with Chris Conklin's minor change; adding "Solder may extend
> 0.010 inches on the circuitry underneath the soldermask at the
> interfaces of the soldered areas and non-soldered areas."
>
> We are very concerned with the potential for solder wicking down
> adjacent escape vias, particularly at passive and BGA sites where
> soldermask coverage is minimal due to short connecting trace lengths.
> We require these sites to be reworkable at least twice. These areas at
> the bare board level should be closely examined at the earliest
> opportunity.
>
> Therefore we would like to see a tighter requirement for high
> reliability printed wiring boards, allowing the solder to extend at most
> 0.005 inches on the circuitry underneath the soldermask at the
> interfaces of the soldered areas and non-soldered areas.
>
> Regards,
> Karl Sauter
> Sun Microsystems
>
>
> > From: IPC-600-6012 [mailto:[log in to unmask]] On Behalf Of
> Conklin, C J
> > Sent: Wednesday, April 20, 2005 4:02 AM
> > To: [log in to unmask]
> > Subject: Re: [IPC-600-6012] Proposed IPC-6012B Change for SnPb in SMOBC
> >
> > I would agree with the wording as proposed by Clarence Knapp with one
> minor
> > change just for consistency:
> >
> > "Solder may extends 0.010" on the circuitry underneath the solder mask
> > at the interfaces of the soldered areas and non-soldered areas.
> > Final finish used to preserve solderability 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."
> >
> > Interestingly, I just had this same conversation with Mark Buechner on
> > Friday. We build very few solder plated and selectively striped PWBs.
> > However, we do produce a significant number of conventional SMOBC
> PWBs with
> > HASL. From time to time, we end up with small areas where the circuit
> has
> > solder mask over solder. Criteria that would allow this to be
> accepted on a
> > limited basis would have our approval. Therefore, we would vote yes for
> > criteria that covered both the encroachment under the mask at the
> interface
> > for selectively stripped parts and solder, or whatever final finish
> is being
> > used, under solder mask on interior circuits as described by Mike Hill.
> >
> > Best regards,
> >
> > Chris Conklin
> > PWB Quality Engineering
> > Lockheed Martin Systems Integration - Owego
> > 1801 State Route 17C MD0409
> > Owego, NY 13827
> > Phone: 607-751-4251 FAX: 607-751-7714
> > e-mail: [log in to unmask] <mailto:[log in to unmask]>
>
>
> > -----Original Message-----
> > From: John Perry [mailto:[log in to unmask]]
> > Sent: Tuesday, April 19, 2005 9:05 AM
> > To: [log in to unmask]
> > Subject: [IPC-600-6012] Proposed IPC-6012B Change for SnPb in SMOBC
> >
> > 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
> > [log in to unmask]
> > 1-847-597-2818 (Phone)
> > 1-847-615-7105 (Fax)
> > 1-847-615-7100 (Main)
> >
>
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