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DPAK and SOT-89 Can be a bit tricky...
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Nick B View Drop Down
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Joined: 02 Jan 2012
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Points: 2096 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Nick B Quote  Post ReplyReply Direct Link To This Post Topic: DPAK and SOT-89 Can be a bit tricky...
    Posted: 9 hours 11 minutes ago at 9:38pm
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There seems to be a strange behavior when using an FPX component (downloaded from POD) with the Footprint Expert. I do not know if I am doing something wrong or there is an issue with the Footprint Expert.
 
The component is Onsemi SZMM3Z5VST1G, I am using PCBFE 26.08, 8/8/2026
When I load the FPX file, the pad size is rr70_83r10.
After recalculating the file, the pad size is rr70_52r10.
To activate the Calculate button I wrote the same value in one of the data boxes.
 
If I create the component manually using the same data that on the downloaded component, the pad size is rr70_52r10.
 
What is happening?

ANSWER:
The part on POD has the manufacturer recommended pattern.


When you recalculate, the manufacturer recommended pattern resets to the default IPC rules. You need to reinsert the mfr. recommended pattern dimensions.

Quote
Thanks for your explanation. I did not realize that, good point! My idea downloading the footprint was to check the distance used by the Footprint Expert in the pin in contact with pad (L), but the data of the component is missing:


How do you resolve this situation?

For this component, in my humble opinion, the manufacturer recommended land pattern could create problems in the assembly process. The Y=0.83mm for a pin with b(max)=0.4mm, could allow to the component to move in the land pattern if there is any problem with the paste mask or the heat or something else...

ANSWER:
If the component manufacturer only provides a Minimum 'L' dimension, using the manufacturer recommended pattern solves the missing Maximum value.

Also, Diodes may carry high voltage current, and the manufacturer wants to enlarge the pads to carry the current.

Same with DPAK voltage regulators - they carry high current and it may be wise to use their recommended pattern.

You're on the right track.
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