Sherman,
        I have encountered this once from a customer during design/proto
phase, but steered them away from it in final layout by stressing
concerns of overall reliability of assembly (they were working towards
Bellcore compliance). Bellcore TR-NWT-000078, Sec 2.2 addresses general
electrical and mechanical integrity and would probably consider this to
be 'novel or new technology' which would require demonstrated
reliability through accelerated testing or modeling. In addition, Sec
7.1.2.2.5 specifically prohibits 'piggybacking' of components in
production assemblies. Talk to your designer and stress the fact that
Bellcore standards are written to assure the highest quality and
reliability levels, and should be used as a guideline for non-standard
assembly practices even when building to IPC. Appeal to his obvious
concern for the utmost product integrity (guilt trip) and he should see
the light....

Mike McMonagle
PCA Process Engineering Supervisor
K*Tec Electronics
1111 Gillingham Lane
Sugar Land, TX  77478
(281) 243-5639 Phone
(281) 243-5539 Fax
[log in to unmask]

> -----Original Message-----
> From: Sherman Banks [SMTP:[log in to unmask]]
> Sent: Monday, October 05, 1998 3:55 PM
> To:   [log in to unmask]
> Subject:      [TN] ASSY: stacking 1206 chip resistors
>
> Hi Folks,
>
> We've got an engineer who wants to stack 1206 resistors 3 high in
> order to
> achieve a larger power rating. While it is intuitively obvious to us
> that
> this is NOT the way to go, we are at a loss to find any published
> documents
> that caution or forbid the practice.
>
> Can anyone cite a published source that can give more specific "rules
> or
> guidelines" on this subject.
>
> We've searched, J-STD-001, SM-780, SM-782, A-610, and R-700
>
> Help!!!!!
>
> REGARDS
> Sherman Banks
> [log in to unmask]
> 408/481-6047
>
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