TECHNET Archives

October 1998

TechNet@IPC.ORG

Options: Use Monospaced Font
Show Text Part by Default
Show All Mail Headers

Message: [<< First] [< Prev] [Next >] [Last >>]
Topic: [<< First] [< Prev] [Next >] [Last >>]
Author: [<< First] [< Prev] [Next >] [Last >>]

Print Reply
Subject:
From:
Paul Klasek <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Tue, 6 Oct 1998 11:21:04 +1000
Content-Type:
text/plain
Parts/Attachments:
text/plain (190 lines)
Hi David ; Phill ; Steve
I thought about the deadness of MIL 2000 A ; than I thought lets tackle
it practically .
The standards (like the filet's "fill") are shifting fast nowadays ;
best is to validate whatever you do = test ,
unless you're directly tied to (some) standard .

Phill what does the 275 throw on this subject ? ; don't have this one .
The J 6.4.3.1. (stacking) basically allows it (documented; the way I see
it ) as the stack becomes one part (take a battery & holder ; pin and
wire ; and other "legal" examples of proximity requirements) in
relations to other on board ;
the electrical spacing is invalid note in this (resistive) application
(heat spacing would be more of the concern) .
Read blindly it can be taken as a "rule" ; still what is the "minimum
el. spacing" = defined by application ? = joint ?
The way I interpret the J is : it's telling you > you create a
(documented DWG) clause applicable to 6.4.3.1. as the special cases (
again that splendid term > intuitively obviously ) can not be possibly
all listed in J .
Reading FDA guidelines for bedtime's I became an part time lawyer too
Still ; is gray black or white ; beats me

Indeed ; I presumed this wasn't a satellite card ( intuitively obvious
?) ; perhaps a rush presumption .

Thanks  folks                                           Paul

        PS
        Sherman ; Steve's right : horses for courses : what is it ; one
of the surreal one's ?


> From:         David Ratte[SMTP:[log in to unmask]]
> Sent:         Tuesday, 6 October 1998 9:10
> To:   [log in to unmask]
> Subject:      Re: [TN] ASSY: stacking 1206 chip resistors
>
> First of all, I know this is a dead document, but since you were
> looking for anything that addresses this issue, paragraph 4.23.3.1 of
> MIL-STD-2000A specifically addresses stacking of chips: (page 16)
>
> 4.23.3.1 Stacking of Chips. Chip devices shall be mounted only to
> printed wiring or parts specifically configured to receive them (see
> figure 7).
>
> Since I don't have my scanner on, I'll tell you that figure 7 shows a
> couple of configurations of stacked 1206 resistors with the words
> UNACCEPTABLE DESIGN beneath them.
>
> I'm sure that there is probably something in IPC-610 about it too but
> I don't have a copy of that handy.
>
> -Dave Ratte
> [log in to unmask]
>
> ----------
> From:  Paul Klasek [SMTP:[log in to unmask]]
> Sent:  Monday, October 05, 1998 6:50 PM
> To:  [log in to unmask]
> Subject:  Re: [TN] ASSY: stacking 1206 chip resistors
>
> Hi Sherman ;
> This may be not the answer you seek ; so : "believe it or not" :
> There are few relatively bizarre practices ; but I'd say whole SMT
> progress is from first glance :
> resistors venting heat standing on side are prescribed quite often ;
> as the reliability guys here often said the less (up to a limit)
> solder
> the more reliable the joint (visible in new cap pad footprints) .
> Not that I'd find res. hooked on corners particularly appealing from a
> lot of other views ; but they live
>
> On your subject :
> I did the same (stacking) in telecom application in past (drop tests;
> vibrating at "railway" frequencies >you name it [calibration mainly) ;
> and still here in R&D runs ;
> as long as you have the heat dissipation (bit impeded in bottom two)
> under control and smear the paste sideways without much mess you have
> no
> problem . 1206 metalisation is actually asking for it (fairly "rich")
> ,
> very robust standard pads will have no problem holding 3 stack .
>
> As long as he's got the track to cope with the stack ; he's in the
> obviously constrained design situation making sense to me .
>
> PS
> You won't find this specific "rules" . Rules, generally, are something
> to quiz constantly anyhow, for a lot of reasons
> PPS
> If you handle them in post reflow assy (like calibrations) try to use
> paste and fine heat jet (with thermocoupler on hand first time) ;
> the bugs will get less shocked than with the traditional wire &
> overblasted tip . Hold the stack with needle from top (drop arm) .
>
> See you
> Paul Klasek
> http://www.resmed.com
>
> > ----------
> > From:         Sherman Banks[SMTP:[log in to unmask]]
> > Sent:         Tuesday, 6 October 1998 6:54
> > 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
> >
> > ################################################################
> > TechNet E-Mail Forum provided as a free service by IPC using
> LISTSERV
> > 1.8c
> > ################################################################
> > To subscribe/unsubscribe, send a message to [log in to unmask] with
> > following text in the body:
> > To subscribe:   SUBSCRIBE TechNet <your full name>
> > To unsubscribe:   SIGNOFF TechNet
> > ################################################################
> > Please visit IPC's web site (http://www.ipc.org) "On-Line Services"
> > section for additional information.
> > For technical support contact Hugo Scaramuzza at [log in to unmask] or
> > 847-509-9700 ext.312
> > ################################################################
> >
>
> ################################################################
> TechNet E-Mail Forum provided as a free service by IPC using LISTSERV
> 1.8c
> ################################################################
> To subscribe/unsubscribe, send a message to [log in to unmask] with
> following text in the body:
> To subscribe:   SUBSCRIBE TechNet <your full name>
> To unsubscribe:   SIGNOFF TechNet
> ################################################################
> Please visit IPC's web site (http://www.ipc.org) "On-Line Services"
> section for additional information.
> For technical support contact Hugo Scaramuzza at [log in to unmask] or
> 847-509-9700 ext.312
> ################################################################
>
> ################################################################
> TechNet E-Mail Forum provided as a free service by IPC using LISTSERV
> 1.8c
> ################################################################
> To subscribe/unsubscribe, send a message to [log in to unmask] with
> following text in the body:
> To subscribe:   SUBSCRIBE TechNet <your full name>
> To unsubscribe:   SIGNOFF TechNet
> ################################################################
> Please visit IPC's web site (http://www.ipc.org) "On-Line Services"
> section for additional information.
> For technical support contact Hugo Scaramuzza at [log in to unmask] or
> 847-509-9700 ext.312
> ################################################################
>

################################################################
TechNet E-Mail Forum provided as a free service by IPC using LISTSERV 1.8c
################################################################
To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body:
To subscribe:   SUBSCRIBE TechNet <your full name>
To unsubscribe:   SIGNOFF TechNet 
################################################################
Please visit IPC's web site (http://www.ipc.org) "On-Line Services" section for additional information.
For technical support contact Hugo Scaramuzza at [log in to unmask] or 847-509-9700 ext.312
################################################################


ATOM RSS1 RSS2