Once upon a time-
We included a requirement that leads like those in DIP devices be trimmed
(when required) with tools or tooling that did not impart stress on the
component body. I still have one of these .040 Shear cutters (not flush
cutters) specifically made for DIP leads. It's been a while since we
specifically addressed the possibility of component damage, but it was an
issue at the time and there is a significant amount of impact for the
component. So for discussion purposes it might be prudent to consider.
While we are there, we also required coverage of the lead end once it was
cut since they were iron based and there are corrosion properties different
than copper to consider.
Mel Parrish
[log in to unmask]
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Bissonnette,
Jean-Francois
Sent: Thursday, October 31, 2002 9:03 AM
To: [log in to unmask]
Subject: Re: [TN] Lead protrusion
Agreed with all that was said about the drawings overruling IPC however I
was
face with a situation regarding electrical clearance once that was not very
obvious
at first but could turn into some monster if all conditions were met.
We ask our suppliers to build as per Class 2. All the leads were within the
max
lenght. On a particular IC, a lead bent horizontally would not violate
electrical clearance,
but... if two pins (side by side) would be bent toward each other while
being manipulated
(and we had close calls a few times) a short could have occured. We had to
ask a specific
lenght to avoid mishaps.
At first I assumed that the leads on your boards would not cause that and
did not replied...
but just in case... assuming is not always the right thing to do!!!
JF
-----Original Message-----
From: Keith Calhoun [mailto:[log in to unmask]]
Sent: Thursday, October 31, 2002 8:05 AM
To: [log in to unmask]
Subject: [TN] Lead protrusion
We are having a vigorous discussion about how to deal with lead
protrusion on our thru hole boards. We build mainly IPC class 3 boards,
and have two Contact Systems CS400-D thru hole insertion machines that
we use to populate these boards. Discrete parts are not a problem, as
the leads are crimped to retain the parts in the boards for wave
soldering. Our area of concern is DIP packages along with sockets, and
connectors. When we insert DIPs we clinch two opposing corner pins,
connectors and sockets are retained with temporary solder mask (goop).
we are finding that the leads on these parts tend to exceed the max lead
protrusion permitted for class 3 boards when used in .06 nominal
thickness boards, but do not want to get into the quagmire of trimming
leads and inspecting or reflowing after trimming. These boards will
meet the class 2 requirements, and there is no danger of violating the
minimum electrical spacing requirements when these boards are installed
in our systems.
Anyone else having this problem? If so, how did you resolve it? Your
support is greatly appreciated.
Keith Calhoun
Manufacturing Engineer
Sierra Research, an Integrated Defence Technologies company
485 Cayuga Road PO Box 222 Mail Stop 334
Buffalo
New York
14225
USA
Fax: (716)631-7849
Work: (716)631-6434
<[log in to unmask]>
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