Will solder flux residue have any impact on the performance of an IA ?

Thread Starter

Dritech

Joined Sep 21, 2011
874
Hi all,

I am doing a circuit using the INA333 instrumentation amplifier, with an input voltage in the low mV range.
As solder flux, I am using cheap NT ZJ-18 Yellow paste and Kester SN63PB37 as solder.

Question 1: Is the solder quality any good? or is there room for improvement? Any suggestions would be highly appreciated.
Question 2: I did my best to clean off the flux, but some of the flux residue remained between and under the leads. Will this affect the performance of an IA ? (on the short and long run)
 

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Yaakov

Joined Jan 27, 2019
3,492
The Kester solder is an excellent one, no problems there. Your cheap flux has a bad reputation but unless it is corrosive, which I can't figure out from what is online, there is not problem with the excess being on the board. That said, I would try to flush it with 99.9% (anhydrous) or at least 96% isopropyl alcohol and then don't apply and current until it is well evaporated.
 

Thread Starter

Dritech

Joined Sep 21, 2011
874
Thank you Yaakov. So any flux residue left between and underneath the leads should not degrade the quality of the signal or the performance of the IA, correct?
 

Thread Starter

Dritech

Joined Sep 21, 2011
874
Use a brand new, clean toothbrush when you apply the alcohol to assist in the cleaning.
Hi Schmitt Trigger, I used the Menda 35688 brush, but flux can still be seen underneath the leads (as shown in the photos). I think the best option would be to use an ultrasonic bath, something which i do not have :(
 

MisterBill2

Joined Jan 23, 2018
9,267
Some solder flux will absorb moisture and cause electrical leakage. And some oof it will hold dust and the dust will lead to electrical leakage. How much of a problem that would be will depend on the connected circuit.
 

Ian0

Joined Aug 7, 2020
3,237
Use isopropanol, (acetone is very effective, sometimes too effective as some plastic components will dissolve in it).
Toothbrush is excellent (though most toothbrushes will dissolve in acetone).
I spray the board with isopropanol, then use a 40mm diameter nylon rotary brush in a battery-operated power drill. It looks like overkill but it shifts the flux, and also dislodges any SM components that look as though they might be soldered but aren't.
 

BobTPH

Joined Jun 5, 2013
3,658
I think perhaps you are overdoing the flux in the first place. My boards don’t have that kind of residue before cleaning. I just use a liquid flux pen for soldering SMT parts, lightly painted onto the pads.

Bob
 

MisterBill2

Joined Jan 23, 2018
9,267
Given that we do not know anything about the PCB being soldered or the condition or method of soldering, at this point all is good advice based on what works for us.
 

DickCappels

Joined Aug 21, 2008
7,704
This is very simple. I remember reading about how they measured noise in opamp circuit at National Semiconductor. One important step was to clean all of the flux from the PCB board before the test.
 
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