thanks for your comments
as an electrical issue i have verified with the mfg that floating many
of the pins is ok
i had not thought specifically about the stress issues you mention
i suspected that this was a marginal idea at best but wanted to at least
fully consider it
i think you have put the nail in the coffin
(unless someone else starts an intelligent fight with you!)
has anyone seen this done on commercial boards?
Dennis Saputelli
Harry Selfridge wrote:
>
> If this is a product, I advise against your idea. If it is an in-house
> project that will only be used in controlled conditions, it will probably
> work - for a while.
>
> Shorts through the solder mask are unlikely; however, some of the problems
> I see are:
>
> - The package will have uneven stresses on the leads unless the same
> geometry of leads is used on each side.
> - Fewer soldered pins means less physical strength between chip and
> board. Vibration, temperature cycles, etc. become more of a concern for
> possible solder joint failure at the pins.
> - Because the surface of the solder mask is above pad level in most cases,
> the unused leads will be stressed upward (or the soldered leads will not
> be down flush against the pad when soldered. If you run a trace under
> solder mask, under an unused pin, the upward distortion of the unconnected
> pin will be even more exaggerated.
> - Unused pins are not always "unused". Sometimes they are connected to the
> substrate, and should be returned to Vcc, Vee, or Vdd. It depends on the
> chip technology in use. I'm always wary of floating chip bond-outs.
>
> In my view, for anything except a quick-and-dirty in-house project, this is
> a bad idea.
>
> At 06:13 PM 6/7/02 -0700, you wrote:
> >i've got a 144 pin PQFP 0.5mm pitch
> >there are only a small number of connected pins, maybe a dozen or so
> >excluding power
> >
> >i am thinking about deleting a lot of unused pads to possibly open up
> >top side routes and reduce inspection and bridging concerns
> >
> >am i crazy?
> >do you think the leads will short thru the solder mask to traces below?
> >
> >is this good practice even if i don't run traces there, i.e. will it
> >solder and align properly with missing pads?
> snip
--
___________________________________________________________________________
www.integratedcontrolsinc.com Integrated Controls, Inc.
tel: 415-647-0480 2851 21st Street
fax: 415-647-3003 San Francisco, CA 94110
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
* To post a message: mailto:[EMAIL PROTECTED]
*
* To leave this list visit:
* http://www.techservinc.com/protelusers/leave.html
*
* Contact the list manager:
* mailto:[EMAIL PROTECTED]
*
* Forum Guidelines Rules:
* http://www.techservinc.com/protelusers/forumrules.html
*
* Browse or Search previous postings:
* http://www.mail-archive.com/proteledaforum@techservinc.com
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
