IPC/EIA J-STD-001C says this: 6.4.2.1 Mounting of Parts on Parts (Stacking) When part stacking is permitted by the assembly drawing(s)/documentation, parts shall not violate minimum electrical clearance between other parts or components such as terminals or other chip components.
IPC-HDBK-001 w/Amendment 1 says: Except when required in high frequency applications, stacking of components should not be permitted in initial design. Stacking involves the soldering of surface mount chip components on top or along side of each other. Stacking usually occurs when the existing design must be modified to incorporate additional components on the assembly and the PWB does not permit proper mounting of the device. Stacking should be documented on the assembly drawing. Stacking of resistors on top of each other is not recommended because the resistance of the bottom resistor could be changed by the presence of solder on the deposited element. When resistors are mounted on their sides, the deposited element(s) should be positioned towards the outside. Bridging components across other components is not recommended, as shown in Figure 6-24.
IPC-A-610C is mute about stacking so no visual acceptance criteria; users will have to develop their own.
IPC-2221 says in 8.1.1.3 Surface Mounting: . . . Unless a component or part is specifically designed to accept another part into its configuration, there shall be no stacking (piggybacking) of components or parts (see J-STD-001).
So acceptable is in the eye of the beholder. Or the designer. Or the user. Or someone that determines that they need to do it for their specific application and documents it by putting it on the drawings.
This is about the best I can elaborate.
Jack
>>> [log in to unmask] 09/27/01 04:22PM >>>
Jack,
Are you saying stacking of components are acceptable? Please elaborate your comments.
re,
Ken Patel
Jack Crawford wrote:
> The official release of 7721 Change 2 can be downloaded FREE from the IPC Website http://www.ipc.org and select the link to "On-Line Resources . . ." and on the new page to "IPC Documents for Download".
>
> jack
>
> >>> [log in to unmask] 09/27/01 01:03PM >>>
> Tim,
>
> We're often asked to stack chip components and perform other odd
> modifications. We have also added a new procedure to IPC 7721 called
> Component Modifications and Additions. You can preview our version of this
> procedure, including images of stacked components, on our web site at:
> http://www.circuittechctr.com/guides/6-3.htm
>
> Jeff Ferry, CEO
>
> Circuit Technology Center, Inc.
>
> Chairman
>
> IPC Repairability Committee
>
> On Wed, 26 Sep 2001 09:10:38 -0500, Tim Devaul <[log in to unmask]>
> wrote:
>
> >Good morning,
> >
> > I am in the middle of a slight disagreement between a couple of our
> company's organizations. It is over stacking
> >SMD chips, specifically 0603s. In a temporary rework fix engineering wants
> to stack and solder one chip directly on top of the other. Does anyone have
> any experience positive or negative concerning this practice?
> >
> >Tim DeVaul
> >Quality Assurance Training and Audit Supervisor
> >Philips Broadband Networks, Inc.
> >100 Fairgrounds Dr.
> >Manlius, New York 13104
> >Tel: (315) 682-9105 Ext. 2403
> >Fax: (315)682-9006
> >Email: [log in to unmask]
> >
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