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Resistor's resistance drifts up after electroplating

We are a resistor manufacturer and we're faced with a problem while plating nickel over the 10 ohm resistors. We found that the resistance before electroplating is in the tolerance but after the electroplating process, the resistance driftup with minimum 0.059% and the most 0.972% which will cause it out of spec. As your knowledge, the 10 ohm resistors are plated by using 72.3A within 87 minutes. Is that the high current effect the resistance and cause it out of spec? Or you know the real causes of it?

Terence Tan

2006

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Terence,
I don't understand the second part of your question. Are you referring to plating load amperage and plating time? What is the resistor substrate makeup (before plating)? There are other metals with better resistance values than nickel. What type of nickel bath are you using? If your dealing with tight specs, your nickel bath has to be of the highest purity. Organic contamination and co-deposited metallic impurities can throw you out of spec. Please post the additional info. so I could better help you. Regards,

Mark Baker

2006

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First of two simultaneous responses --

I would check the following,

1. Check if the resistor is properly covered with dielectric over coat. Most of the time, the laser trench is not properly covered and this could cause the drift after plating.

2. Check if the edge wrap around termination (if polymer Ag paste) is properly cured. If the paste is not cured properly you might see this effect after plating.

3. Try a STOL (Short time over load) test before plating and see if you see a drift. This will tell you if the current you are using to plate the resistor is causing the drift issue. If thats the case you have to select a proper resistor paste for such low tolerances or check your laser trimming process. (low power, residue in trench, etc etc)

Good Luck

Karthik Thambidurai

2006

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Second of two simultaneous responses -- 2006

Thanks for your reply.
yes, 72.3A is the plating load ampere and 87 minutes is the plating time. the resistor substrate is made up by alimina. we are using watt's dull nickel bath.
is that the organic contamination still strongly effect the resistance compare to the co-deposited metallic impurities. we are dealing with 0.7% tolerance and we are using high purity nickel.

Terence Tan

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First of three simultaneous responses --

Karthik Thambidurai,
thanks for your suggestion.

1. we check the resistors by 40 times microscope to make sure it is properly covered by dielectric overcoat.
2. we are using sputtering technique to wrap around the termination.
3. what is the recommended type of the dielectric (overcoat) paste using for cover the trim?
4. what is the recommended cure thickness?

Terence Tan

2006

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Second of three simultaneous responses -- 2006

Karthik Thambidurai,
We are using a stol tester after electro plating by solder the resister up to PCB board.
but we unable to solder it up before plating. so do you got any better idea for stol?

Terence Tan

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Third of three simultaneous responses -- 2006

Hi Terence,
To answer your question, metallic co-deposition can play a role in the increase of resistance to a greater extent than organic impurities will. Of course it would all depend on the respective levels. If you look at a electrical resistance chart for various metals you can note the differences. If you have had the Ni bath checked lately for inorganics (iron and lead would be a few of the common types), then you can rule out the plating solution and know you have a high purity Ni plate. If not, your Ni supplier may check the common contaminants free of charge for you.
Mr. Thambidurai seems more familiar with the actual process for resistors than I am, so his advice should be held in high value and respect. I'm a plating guy just sharing experiences I've had over the years. Good Luck!

Mark Baker

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First of two simultaneous responses -- 2006

Hi Terence,

You could do a STOL test without having to solder the terminations. You could use a very good clip contact (alligator clip will do) and apply 2.5 times the rated current to check if the drift is due to passing of current during plating.

For lower value resistor a good trimable glass would be preferred (Green Glass from Shoei or Dupont would do) on top of resistor before trimming. After trimming the glass should melt and cover the exposed resistor. Any residue (black residue) in the trench should be wiped clean with IPA or DI water using lint free wipe.

Generally the fired thickness of the termination and resistor should be 8-12 microns.

If you couldn't find any cause, it might be due to the resistor material you are using. The best option would be to offset during trim process. Say if you require 10 Ohms offset the value to 9.75 Ohms during trimming and after plating it would be close to 10 ohms. You have to arrive at the offset value by trial and error.

Generally plating is not a suspect as long as you don't see black pads or unplated pads.

Hope this helps...

Karthik Thambidurai

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Second of two simultaneous responses --

The effect of plating current towards resistance value. hi, is that the value of plating current will effect the drift up percentage of the resistance?
if using the lower plating current and use longer time for plating process, will the drift up percentage decrease?

Terence Tan

2006

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2006

Dear Mr. Karthik Thambidurai,
We are using OKUNO OC1614 paste while over-glaze. According to the reading we get by measurement, the resistor's resistance will drift 0 to -9.753%.
is it a normal situation?

Terence Tan

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2006

Hi Terence,

Are the measurement readings from STOL test? If so, -10% is quite unusual. Also, if I understand correctly you had mentioned earlier that the drift was positive ... are you seeing a negative drift now? How good is your TCR?

It is normal to see 2 to 3% drift after plating with low value resistors like 10 Ohms. Anything more than that is unusual atleast from my experience.

Areas to check,

1. Firing profile
2. Trim speed & kerf depth
3. Or Contact Paste vendor.

Good luck ...

Karthik Thambidurai

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We are using OKUNO OC1614 paste for over-glaze process. According to the reading we get by measurement, the resistor's resistance will drift 0 to -9.753% after firing.
is it a normal situation?

Terence Tan

2006