Patterns that combine multiple pads to a single pad?

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psabadin
Posts: 4
Joined: 06 Nov 2012, 12:13

Patterns that combine multiple pads to a single pad?

#1 Post by psabadin » 18 Aug 2014, 17:18

Is it OK to make a pattern that combines multiple pads into a single pad on a PCB pattern?

Routing is tight! I have an IC that has many pads that are logically the same, e.g. VCC has three pads right next to each other and GRD has multiple pads including a thermal pad. It seems as though a pattern could be made that combines these pads to a single pad. This makes routing easier and passes more current in a fatter trace on the PCB.

Is it OK to change the first pattern below to the second pattern? (combined pads have same logical label, GRD, VCC ...)

Image -----> changes to -----> Image

Good? OK?

Thanks

Serg
Technical Support
Posts: 345
Joined: 09 Jun 2010, 08:12

Re: Patterns that combine multiple pads to a single pad?

#2 Post by Serg » 19 Aug 2014, 08:12

Hello,

You can change this pattern. But you need to consider a design and IC recommendations.

Serg Luts
DipTrace Team

psabadin
Posts: 4
Joined: 06 Nov 2012, 12:13

Re: Patterns that combine multiple pads to a single pad?

#3 Post by psabadin » 21 Aug 2014, 11:51

Thank you, sl_sergey,

Other than thermal (which is low), abs maximum electrical values, and logical pinouts, are you suggesting something more to consider?

I am most interested in whether the reflow process will work by making a single large pad that covers three QFN pads that are next to each other.

The chip is a new TI DRV8850 and the data sheet is the poorest I have seen from TI. The chip also comes only in a QFN package (today) which makes it hard to reflow with my hobbyist "hot plate reflow" technique.

Can you give any further thoughts about combining multiple pins (GRD - ground) into a single pad and any reflow problems for that?

Thank you,
Paul

Serg
Technical Support
Posts: 345
Joined: 09 Jun 2010, 08:12

Re: Patterns that combine multiple pads to a single pad?

#4 Post by Serg » 22 Aug 2014, 05:04

Hello Paul,

Thank you for question. Unfortunately we cannot give any recommendation by this theme.

Serg Luts
DipTrace Team

Abbas_BrainAlive
Posts: 6
Joined: 18 Oct 2018, 12:20

Re: Patterns that combine multiple pads to a single pad?

#5 Post by Abbas_BrainAlive » 18 Oct 2018, 12:30

Hello Paul,

My requirement is very much closer to yours. I too want to merge multiple pads into one. But my objective is a bit different. Designing polygon/non-symmetric pads is very much easier and faster when you use discreet symmetric shapes and merge them into one. That's what I want to do. The only problem is the DRC. Even if I number all the discreet pads constituting a single non-symmetric pad of a component, Diptrace considers them separate individual pads. Those red circles are very distracting, especially when you are designing a complex system.

Is there any way to remove those red "error" circles?

There is no such thing as creating exceptions in Diptrace DRC, as far as I know!

If anyone could please suggest a workaround, I would be really grateful.

Best regards,
Abbas.
Last edited by Abbas_BrainAlive on 18 Dec 2018, 10:28, edited 1 time in total.

Alex
Technical Support
Posts: 3241
Joined: 14 Jun 2010, 06:43

Re: Patterns that combine multiple pads to a single pad?

#6 Post by Alex » 19 Oct 2018, 09:15

You can link one pin to multiple overlapping pads when you attach the pattern to component. Then you will get rid of DRC errors in PCB Layout as overlapping pads will belong to the same net.

Abbas_BrainAlive
Posts: 6
Joined: 18 Oct 2018, 12:20

Re: Patterns that combine multiple pads to a single pad?

#7 Post by Abbas_BrainAlive » 20 Oct 2018, 03:41

Thanks a lot, Alex, that worked!

But I am still open to quicker methods, like doing something collectively, on a group basis. For example, selecting all the target pads together and applying/modifying a certain setting all at once.

I would be grateful.

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