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February 2000

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Subject:
From:
"Hiteshew, Michael" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Wed, 9 Feb 2000 12:54:23 -0500
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Hello Miguel,
        I'm on the design end of circuit card assemblies. Ron Dieselberg is
indirectly pointing you at the proper solution. From a practical standpoint,
I suspect that whether the leads are trimmed at .060" or .065" from the
bottom of the board is irrelevant at the next assembly level. Whoever picked
out the connector probably didn't realize the implication of the mechanical
tolerance issue as it relates to the specification regarding max lead
protrusion on the finished assembly. However, that doesn't free you from
your obligation to meet the spec.
        My suggestion is that you bring this to the attention of the
engineering department. If you are a subcontractor, bring it up with your
liaison. Ron is correct in pointing out that the drawing supercedes
everything else. First, for the short term, ask for a waiver regarding lead
protrusion for the connectors involved. This will spark someone at the
design end to do a dimensional and tolerance analysis of the assembly.
Assuming five or ten mils of additional lead protrusion is not a problem
(and it may be - I don't know), ask to have the drawing modified to show
(graphically or with a note) the max lead protrusion allowed for that
assembly; or for a permanent waiver.

 Michael Hiteshew
 Lockheed Martin Launching Systems
 [log in to unmask]
 (410) 682-1259


> ----------
> From:         Miguel Vallejo[SMTP:[log in to unmask]]
> Subject:      [TN] Dimension variation
>
> Hi,
> I'm in the assembly end of the stick and have a situation that requires
> insight from the IPC group and parts manufacturers, although everyone is
> welcome to respond.
> 1. J-STD-001B, 1.3.1, states "Actual measurements of specific part
> mounting and solder fillet dimensions and determination of percentages
> are not required except for referee purposes."
> 2. If connector, sockets, headers, etc. are manufactured to present a
> lead protrusion of .060 on a .062 PCB and .030 on a .092 PCB (I'm
> assuming this is the manufacturer's target from what I've seen).
> 3. Considering a scenario where PCB and parts fabrication tolerances are
> in opposite directions (ex. PCB on the min. side and part on the max.
> side), which results in an increased lead protrusion, .062-.065.
>
> Is one to interpret the J-STD statement as expecting such a variation to
> be acceptable on a class 3 assy, since we're not required to measure for
> these dimensions? I've concluded so, but others here think we are bound
> to the .060 max.
> However, how is one expected to follow recommendations on J-STD-001B,
> 1.3.1, and meet the .060 max. lead protrusion on this kind of scenario?
> I hope I presented a clear idea of my situation.
> Thank you for any help.
>

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