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. 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