Rich,
Let me state the obvious :
1. Is it possible to have your customer go to a SMD resistor and
eliminate the pth?
2. Assuming your customer DFM is acceptable for spacing of conductive
features, what is your lead length protrusion
from the pth? Can these be trimmed before clinching so as not to
reach to the conductor?
3. Is it possible to have your customer reroute the conductor(s) to
alleviate all areas where your resistors are clinched?
4. If none of these are possible, I think Phil has the best answer,
although costly, trimming.
DT
At 12:32 PM 9/28/00 -0400, Phil Nutting wrote:
>Rich,
>
>We ran into a similar problem only the failures occurred while the product
>was still in house. Our solution was to manually trim all leads prior to
>release from PCB build. What a labor hog! I'd love to find a better
>solution.
>
>Regards,
>
>Phil Nutting
>Manufacturing Engineer
>Kaiser Systems, Inc.
>126 Sohier Road
>Beverly, MA 01915
>ph: 978-922-9300
>fx: 978-922-8374
>[log in to unmask]
>
>
>-----Original Message-----
>From: Rich Lasko [mailto:[log in to unmask]]
>Sent: Thursday, September 28, 2000 11:37 AM
>To: [log in to unmask]
>Subject: [TN] Lead Clinching over soldermask
>
>
>Good morning everyone!
>
>We are currently investigating a failure mode that has happened on a few of
>our customer's assemblies.
>
>The problem is as follows (a little background):
>
>We have three confirmed occurrences in which a through-hole clinched
>resistor lead has shorted out with a non-common conductor on the "solder
>side" of the board. All the conductors are coated with soldermask, however,
>after about four (4) months in the field (in which the unit had been working
>properly) the resistor lead had penetrated or pierced through the soldermask
>and "shorted" out with the adjacent conductor. The cause of the penetration
>is unknown at this time. We gently pulled the resistor lead slightly away
>from the adjacent conductor and the unit began working properly again (short
>was gone). We inspected the soldermask at 40X but did not see any copper
>exposure.
>
>IPC-A-610C (Section 5.2.7.2) states that "The lead is clinched toward an
>electrically non-common conductor, violating minimum electrical clearance"
>is a defect (all three classes). Our Auto-insertion machines are set up for
>a 45 degree angle clinch. (However, in these cases the clinch was below 45
>degrees...so it did appear the clinch was much tighter to the board than we
>would like)
>
>So....The issue we have are the following:
>
>The design of the board is such that the clinched resistor lead will always
>overlap the adjacent non-common conductor. Our detection for this condition
>has always been ICT and Functional Testing (which it will detect if the
>condition exists immediately). But unfortunately the failure did not occur
>until the unit was in the field for awhile. Has anyone else ever
>experienced this problem? If so, what steps were taken to resolve it? How
>was is verified? Did you have to rely on visual inspection of the clinch
>over soldermask?
>
>Help!!!!
>
>Thanks
>
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