Mime-Version: |
1.0 |
Sender: |
|
X-To: |
|
Date: |
Thu, 14 Aug 2008 13:43:49 -0500 |
Reply-To: |
|
Subject: |
|
Content-Transfer-Encoding: |
quoted-printable |
Content-Type: |
text/plain; charset="windows-1252" |
From: |
|
Parts/Attachments: |
|
|
A product I am working on recently experienced a higher than normal drop out
both internally and externally due to open traces. Microsection analysis of
several of the failing PCBs found barrel cracks, plating folds, and insufficient
wall thickness.
Our fabrication specification requires "Copper Plating, Annular Ring, Conductor
Spacing, and Solder Mask requirements shall be in accordance with IPC-6012,
Class 3". PCB is 6 layers or IPC Type 3.
I applied IPC-6012 tables 4-2 Sampling Plan and 4-3 Acceptance Testing and
Frequency to give the following:
- Table 4-3 specifies sample frequencies of 2.5 for Plating / Coating Thickness
and 0.1 for Hole Plating Thickness (structural integrity after stress), both per
panel.
- Our lot size was approximately 2000 PCBs, yield is 6 PCBs from an 18" x 24"
fabrication panel, therefore at least 330 fabrication panels would have been
processed.
- From Table 4-2, my assumption is that lot size should be 330 panels, and
the corresponding sample sizes for 0.1 is 125 and 2.5 is 16 (please correct me
if I'm interpreting this incorrectly !).
Some questions:
1. What governs how the fabricator applies the specification to their process.
In other words, does a vendor have freedom to perform (in our case) 125
samples / 16 samples from a single fabrication panel and then pass the other
329 based upon those results, or is there some other specification which
which the vendor must follow for sample identification ?
2. If so, how do I properly convey this to the vendor ?
We have since determined the cause was 1 of 7 sub lots at our vendor was
improperly processed through desmear. It's my feeling that our Class 3
requirement should have caught the failures at the fabricator if proper
sampling / testing was performed - comments ?
Thanks,
Dave
---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 15.0
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL)
To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest
Search the archives of previous posts at: http://listserv.ipc.org/archives
Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815
-----------------------------------------------------
|
|
|