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Solder Mask Defined Variant

Printed From: PCB Libraries Forum
Category: PCB Footprint Expert
Forum Name: Questions & Answers
Forum Description: issues and technical support
URL: https://www.PCBLibraries.com/forum/forum_posts.asp?TID=2303
Printed Date: 16 Nov 2024 at 8:44pm


Topic: Solder Mask Defined Variant
Posted By: ransonjd
Subject: Solder Mask Defined Variant
Date Posted: 26 Feb 2018 at 7:56am
Hi,

Is there a quick way to generate SMD footprint variants for parts?  

I'm looking at power parts where some pins have skinny traces connecting to them, and others have planes. 

I want SMD footprints to prevent uneven solder height due to spreading during reflow.

Thanks,
John


Replies:
Posted By: Tom H
Date Posted: 26 Feb 2018 at 8:14am
By "Variants" are you referring to Library Expert Preferences? 

Can you provide some real application examples? 



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Posted By: ransonjd
Date Posted: 26 Feb 2018 at 10:16am
This is mostly an issue with power components, which require thick traces or pours to certain pads for electrical or thermal dissipation reasons.

An example would be a dual power transistor in a leadless package where the sources and drains have to be directly connected to pours for heat dissipation, but you want skinny traces to the gates to minimize capacitance. With NSMD pads, the pour-connected pads end up with extra exposed copper.  They are effectively starved for solder paste, since the paste only covers the nominal pad area. 

Posted By: Tom H
Date Posted: 26 Feb 2018 at 10:44am
All of this can be done in FP Designer. 

FP Designer is available in both V2018.02 Library Expert Pro and Enterprise. 

You have complete pad stack design and placement control. 



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Posted By: ransonjd
Date Posted: 26 Feb 2018 at 10:53am
Can it be done just through a preferences file? I often already have a part entered that I'm using in a new way, and I need a version with NSMD pads. It would be great if I could just pick a set of preferences and pop out a new footprint. If not, it's no big deal.

Posted By: Tom H
Date Posted: 26 Feb 2018 at 10:59am
The preference file only has settings for "Terminal Lead" styles like Gull Wing, J-Lead, Flat Lead. 

Preferences are mainly used for the Calculator to auto-generate patterns. 

However, you have 100% full editing rights to adjust the Toe, Heel and Side goal for any Terminal Lead form. 

You also have a preference for Thermal Tab Paste Mask Reduction.

I think you need the ability to create custom pad stacks and FP Designer does that. 



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