Author Topic: Create a shortcircuit between two PCB pads  (Read 670 times)

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Offline jm_sanz

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Create a shortcircuit between two PCB pads
« on: August 23, 2022, 09:44:52 am »
Good morning everybody,

I am trying to shortcircuit the drain to source pads of a mosfet (attached) trying not to have any influence on the thermal model of the system.

[attachimg=1]

For this, I have tried using some solder tip but pads do not join together. I have found this copper tape that might to the job but for sure not as good as soldering as it includes some thickness.

https://www.3m.com/3M/en_US/p/d/b00041333/

Any tip for joining both pads?

Thank you :)
José Miguel Sanz Alcaine
Infineon Technologies Austria AG
Specialist Device Performance Analysis
 

Offline jpanhalt

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Re: Create a shortcircuit between two PCB pads
« Reply #1 on: August 23, 2022, 09:59:39 am »
Suggestions: Short pieces of wire or "zero" ohm resistors.  If you want copper strip, get copper flashing at a hardware store.  Hobby shops in the US also sell thin copper sheet.  You can also buy copper foil without adhesive.  The adhesive is no advantage.  I would certainly not rely on it for electrical contact.  It can be removed with some organic solvent.  I would use MEK.
 

Offline Feynman

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Re: Create a shortcircuit between two PCB pads
« Reply #2 on: August 23, 2022, 10:51:16 am »
Not sure, if I understand your intentions correctly, but you want to "bypass" the power dissipation of the MOSFET, right? The resistance of zero ohm resistors is usually higher than typical Rds(on) values of MOSFETs. So maybe that is not what you want in this case.

Most likely solder mask is preventing you from joining the pads with solder. Maybe you can cover the solder mask between the pads with copper tape (or thin aluminum foil) and then try to make a decent low resistance connection with solder (on top of the copper tape)?
 
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Offline jm_sanz

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Re: Create a shortcircuit between two PCB pads
« Reply #3 on: August 23, 2022, 11:53:12 am »
Yes, this was actually what I already tried and got a 1mohm resistance in comparison with the 3mohm of the MOSFET. This is good but not enough for my application. I think this might be due to a poor soldering from the pad to the copper foil. It is kind of tricky as it forms sort of a sandwhich between the pad, the copper foil and the MOSFET.
José Miguel Sanz Alcaine
Infineon Technologies Austria AG
Specialist Device Performance Analysis
 

Offline jm_sanz

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Re: Create a shortcircuit between two PCB pads
« Reply #4 on: August 23, 2022, 12:52:17 pm »
I have found this one which seems very suitable for the application, the thiner the better.

https://basiccopper.com/6x61milcofo1.html

Thanks!
José Miguel Sanz Alcaine
Infineon Technologies Austria AG
Specialist Device Performance Analysis
 

Offline Kean

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Re: Create a shortcircuit between two PCB pads
« Reply #5 on: August 23, 2022, 01:00:57 pm »
I have found this one which seems very suitable for the application, the thiner the better.

Thinner copper sheet is probably going to give worse results.

A quick calculation based on a 4x6.5mm section of 35um copper (approx area between S & D pads) at 25C gives 800uohm, so not much better than the 1mohm you achieved.
The same calculation with 1 mil (25um) copper sheet is 1.1mohm.

You will need thicker copper to get a lower resistance, but that will be harder to solder and may affect thermals.

Calculator used: https://www.omnicalculator.com/other/pcb-trace-resistance
 
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Offline free_electron

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Re: Create a shortcircuit between two PCB pads
« Reply #6 on: August 23, 2022, 02:53:28 pm »
There are preforms available that solder directly on that footprint to short source and drain
Laird makes those i believe
Professional Electron Wrangler.
Any comments, or points of view expressed, are my own and not endorsed , induced or compensated by my employer(s).
 
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Offline jm_sanz

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Re: Create a shortcircuit between two PCB pads
« Reply #7 on: August 24, 2022, 09:26:51 am »
Do you have the name or the reference to look into their website? they have too many products.

Thank you.
José Miguel Sanz Alcaine
Infineon Technologies Austria AG
Specialist Device Performance Analysis
 


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