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Mfr Recommended, Tolerances & Affected Pad Stacks
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Nick B View Drop Down
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Joined: 02 Jan 2012
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Points: 2092 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Nick B Quote  Post ReplyReply Direct Link To This Post Topic: Mfr Recommended, Tolerances & Affected Pad Stacks
    Posted: 5 hours 5 minutes ago at 1:34am
QUESTION:
Quote MINI-CIRCUITS has a wide range of RF devices with non-JEDEC/custom package types, e.g. the selected DLFCG-540+ (Case GE0805C-1) 6-pin SMT ceramic filter.

In this case (and for their other components), the part outline has tolerances both on the termination width E (which is normal) and the pitch G (which, I think, is singular). The same G pitch value is used for their PCB land pattern recommendation, with different tolerances. Note - "Suggested Layout Tolerance to be within +/-.002"

Looks weird to me, at least unusual. As far as I know, the component termination pitch has no related tolerances and has often a BSC (Basic Spacing between Centers) mention.

We faced placement issues with this part and are about to discuss the point with MINI-CIRCUITS.

Below is an IPC-7352 extract that does not help and confuses me. I would have rather see the sentence as "the pin pitch of the land pattern should match the pin pitch of the component datasheet" (or POD, drawing).

I would welcome your thoughts on this topic.

ANSWER:
Manufacturer package tolerances are mostly too robust and not reality. They don't realize that their tolerances impact pad stack calculations and all the drafting outlines that are mapped to the maximum material condition. 

Any package with dimensions like a 0805 package should have a realistic maximum tolerance of 0.15 mm max, 0.10 mm nom. or 0.05 mm minimum. We prefer to use the minimum tolerance of 0.05 because it's realistic.

It’s the goal of every component manufacturer to create packages near the Nominal Package Dimensions and their recommended patterns prove that.


The Mini-Circuits Recommended Pattern does not accommodate their package in the Minimum or Maximum material condition for the tolerances they provide. 

i.e.: if you used the manufacturer package dimensions in the minimum or maximum tolerances, would they fit on the pattern?

Here is the Mini-Circuits Recommended Pattern using their negative tolerance.
Pad stacks are too way robust for their minimum material condition. 


Here is the Mini-Circuits Recommended Pattern using their positive tolerance. 
Not sufficient pad stack for maximum material condition. 


Here is the Mini-Circuits Recommended Pattern using no tolerances. 
Perfect pattern for a package using no tolerances.


It looks like Mini-Circuits did not use their own tolerances when they created their Recommended Pattern. 

Component manufacturers need to make their package tolerances realistic. They should measure the packages coming off the manufacturing line to print the real package tolerances in the datasheets. Don't make up fictious tolerances that don’t match reality.
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