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Stacking chips

Ashok Dhawan

#4152

Stacking chips | 12 May, 2000

I need to install two SMD chips (0805) at one location. I refered to IPC-HDBK-001, fIG 6-24. When I solder the chips side by side, the ceramic side which is placed againgst solder pad- is already touching the solder. While I complete the solder joint, the solder fillet is too close to deposited element. ( As distance between end terminations is more the inner gap between solder pads) My question is :

1. Does any one know a vendor who can supply 5-sided terminations ( similar to Chip Capacitors) for thick film resistors? 2. Which one is less evil: Piggy back chips( not recommended by IPC) or solder touching the component body? 3. Any other idea?

I will appreciate your time for advice.

Ashok

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#4153

Re: Stacking chips | 12 May, 2000

Hi Ashok,

you may look through the archive for "patches - Wolfgang Busko 09:57:37 11/12/1999" it�s exact the same subject. Do you have the newest IPC-standart Jeff is talking about in that thread ? What�s the reason for this measure, component-shortage or power problems ? We managed to avoid this situation, good luck

Wolfgang

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Ashok Dhawan

#4154

Re: Stacking chips | 15 May, 2000

Busko

I could not find anything related to chip stacking in IPC-7711. I guess you meant that some changes will be coming. Probably , a task group is working on that. Can you fax or e-mail that info so that I can have access to that info ?

I will appreciate your help

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#4155

Re: Stacking chips | 16 May, 2000

Ashok: Couldn�t find that part in IPC-7711 either. I was just remembering that proposal from that thread mentioned. So you are still in that position I was at that time. Looking into IPC-D-275 (I have to admit that I have only an old issue in my office) it says "not allowed". Maybe the newest edition looks at it different, you might check for that.

You might also look at IPC-technet archives but it�s no real help for it states nearly the same, there�s a thread from 1998. Are you sure there�s no other way solving that particular problem without stacking components, we always found other solutions together with engineers and designers.

Good luck

Wolfgang

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Chris May

#4156

Re: Stacking chips | 17 May, 2000

You can refer to ANSI/J-STD-001B section 6.4.3.1 which states:

"When part stacking is permitted by the assembly drawing(s)/ documentation, parts SHALL not violate minimum electrical spacing between other parts or components such as terminals or other chip components"

Regards,

Chris May

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#4157

Re: Stacking chips | 18 May, 2000

Chris, one question, which standard allows to put it in the drawings/dokumention? As I said in my old IPC-D-275 it says "no". Did it change with the new edition ? Referring to J-STD-001 in this case seems to me like "I followed only the orders and don�t care if they are right or wrong". I believe Ashok is in that uncomfortable position to decide wether it�s allowed or not. I wish Jeff or somebody who has done some studies on this would say something about changes regarding that problem.

Can�t help any further

Wolfgang

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