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 ################################################################