Richard,

It is generally frowned upon to mount one component over another is such a
way as to require the first to be removed before the second can be removed.

That does not mean you can't do it.

But realize that when you do, other people are going to curse your name
under their breath when they have to work on it... if repair is important...
some products are throw away products and if they fail, they can only be
replaced... others we need to get at to replace bad parts on because they
cost too much to throw away...

Sometimes you have no choice and have to live with it.. but, get the others
in your team to sign up for it before you etch it in copper and warn them of
the impacts to test and repair and the order of assembly. Call a little
'design review' meeting with your manufacturing guys, and the field test
crew... see what they think.

I love 3D puzzles... sounds like you have a good one.. :)

Bravo...


Bill Brooks
PCB Design Engineer , C.I.D., C.I.I.
Tel: (760)597-1500 Ext 3772 Fax: (760)597-1510


-----Original Message-----
From: Richard [mailto:[log in to unmask]]
Sent: Wednesday, January 21, 2004 1:44 AM
To: [log in to unmask]
Subject: [DC] Component stack up / is it OK?

Hi,
I'm working on a board that has a shortage of real estate.
By far the best placement (electrically, ease of assembly etc.) for a large
through hole cap and a 14-pin SOIC on this board would be to have the IC
directly underneath the CAP.
The IC would get reflowed with the other SMDs, and then the CAP would get
waved with the other THDs.
I plan to add vias (and maybe even the silkscreen) on the bottom so that all
the pads can be probed.
My question is if this is a bad practice?  Will the IC have contaminates
trapped on it during assembly because of the CAP?  Environmental issues
aren't a concern, and there is no chance of anything shorting in this
orientation.
I hope it's OK to do this.
Any answers are greatly appreciated.
Thanks,
Richard

----------------------------------------------------------------------------
-----
DesignerCouncil Mail List provided as a free service by IPC using LISTSERV
1.8d
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF DesignerCouncil.
To set a vacation stop for delivery of DesignerCouncil send: SET
DesignerCouncil NOMAIL
Search previous postings at: www.ipc.org > On-Line Resources & Databases >
E-mail Archives
Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16
for additional information, or contact Keach Sasamori at [log in to unmask] or
847-509-9700 ext.5315
----------------------------------------------------------------------------
-----

---------------------------------------------------------------------------------
DesignerCouncil Mail List provided as a free service by IPC using LISTSERV 1.8d
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF DesignerCouncil.
To set a vacation stop for delivery of DesignerCouncil send: SET DesignerCouncil NOMAIL
Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives
Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315
---------------------------------------------------------------------------------