Do circuits built using PCB and using bread board perform the same?

Averagesupernova

Yungman I don't understand you. I accept your last post and will not argue that you have probably seen alot of cases that are like what I described. I did not dare you to dispute what I posted. It seems to like you took my statement as that or that you were stating that such a thing does not need to be proven, which of course it does since there are many components that could be contaminated. I described what happened in the plant and asked if anyone wanted to take a guess at how it was determined that the problem was as I described. The exact wording was as follows: I thought it would be assumed by the readers here that comonents involved with the front end of a digital voltmeter are very high impedance. Finding leakage at these high impedances is not such an easy task.
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Is there some kind of language barrier thing going here? Did I not understand you? Did you not understand me?

yungman

We are going in circles, I repeatedly said I agree with you and said you don't need explain or prove. I back you up on your assertion from my experience as described.

Averagesupernova

You are right, you and I are going in circles. I have acknowledged that you agree with me which is not the point.
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For anyone who actually gets the point:
Was wondering if anyone had an idea how it was proven at the factory what was really happening at the time, using instruments of some sort connected in some manner. Proving leakge that affects the front end of what I recall to be a 10 Megohm input impedance meter by less than a tenth of a percent is not easy. Sorry to say we didn't have yungman running around out there saying: You not need to prove nothing. I know it relays. Must be, I seen it billion times.

yungman

You took it all wrong, I started with a response to back you up.

And now this is uncalled for, I tried to explain politely in a few posts already. Let's just stop here before we really start an argument. Or take it off line, this is physics forum!!!

jim hardy

well, niether of you has to prove it to me.
but anecdotes from real life are always interesting and good way to make a technical point.

i'd say to OP

EEG sounds like it will be connected to some living creature, possibly yourself or a friend.

Most obvious trouble with breadboards like this



is wires come loose and flop against something so make DARN SURE there's no high(> about 15volts) voltage on your board.

Second trouble is as already mentioned, on a breadboard the leads will be longer. That causes trouble with noise pickup, every wire is an antenna.

Third trouble is , as mentioned, on a breadboard you can't "guard" sensitive inputs.
This TI datasheet explains that, see section CIRCUIT BOARD LAYOUT AND ASSEMBLY on page 8, and fig 4. http://www.ti.com/lit/gpn/ina116

Try it and see.

There's several ways to make printed circuit boards at home
i use this one
http://gilmore2.chem.northwestern.ed...garbz2_prj.php
doing the iron-on transfer takes some practice

a Dremel with the drill pess accessory is really handy.

rbj

one thing about modern PCB that makes this a little different is that, in the olden days, the parts used for "thru-hole" PCB and for breadboarding were the same. now you use surface mount parts for PCB, and i can't see how you would use such parts for breadboarding.

yungman

Very hard, we did some, but not a usual practice. Some of the young assembly girls are very good in building those. We usually do pcb for trial run instead, put many small circuits onto one run to cut cost.

jim hardy

i had a high impedance board to do once.

I elaborately guarded the inputs and socketed the relays so the washing machine would get a good rinse around the tracks below relay. I noted drawing to insert relays AFTER wash. Analog hold circuit worked fine, held one part in a thousand overnight with off the shelf polypropylene capacitors.

flux was a terrible problem ten years ago we had it too.
Nova, how'd you determine yours was flux and not a board problem??
We once got some conductive fiberglass.....


old jim

Averagesupernova

One thing a factory has an advantage in is a fairly healthy supply of new and possibly unassembled parts. Or at least lots of assembled samples to play with. This has been pushing 20 years so I have to scratch my head a bit to remember it all. I don't remember specifically how it was determined that it was the relay as opposed to any other part including the PCB but as with any troubleshooting it most likely involved simplify simplify simplify. The part I do remember was testing relays once removed from the board and comparing them to relays that had never been through the solder wave. We used a high-pot tester set up pretty close to 2KV in series with a 10 Megohm or higher impedance voltmeter which was in series with the suspected pins that had leakage on the relay. In an ideal world all of the voltage will be dropped across the relay pins. And with a new relay all the voltage did since there was no reading on the voltmeter. But a tenth or two volts on the meter indicated leakage. Do the math and find out how high of a leakage resistance there was on the relay considering what the meter said, the supply voltage and the Zin of the meter. Just breathing on the relay made the meter reading change.
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Oh BTW, I recall board leakage also but not in this case. Sometimes a good scrubbing would take care of it. Other times it was a vendor problem.

yungman

We had problem by just using flux removal spray and scrub even for a few times. We had to use the freon bath that they used for cleaning high vacuum components to clean it. The freon is very volatile, the main bath at the bottom was heated and the freon vaporized. But the top part of the tank had cooling coils the to make the freon condense back into liquid and drop back down. The bottom has ultra sound for cleaning also.

So all we need to do was hanging the pcb and dipped into the bottom bath and let the ultra sound scrubbed the board, then bring the board up slowly, the condensation ( which is pure clean freon) coming down served to rinse the board. That's the sure way for us to clean the board with very high impedance circuits.

Averagesupernova

Yungman, I recall hearing that prior to my employment freon was often used for cleaning boards. I never had any experience with it.

jim hardy

my boards were built in Idaho where it's quite dry
and i was worried how the product would do in warmer climes
but reports are they do fine in S Florida

indeed that flux residue will absorb moisture from air, seems to me it was a water wash variety to make EPA happy. There was a rash of reports on it around 2000.

that's why i inserted relays after board wash - figured they come from their assembly line clean

and installed the capacitors with INSIDE foil to guarded side.

Thanks fellows

old jim

Topher925

One thing not mentioned here but certainly is an issue in very sensitive applications is piezoelectric effects. With breadboards, everything is through hole and loosely mounted so piezoelectric effects can be ignored. However on PCB's, SMD mount capacitors can function as little microphones and introduce electrical noise from acoustical vibrations from the local environment.

Some of my research requires very sensitive optoelectronics (talking GIGA-ohm feedback resistors on op-amps here) where just clapping your hands in the same room as the device would completely wash out the signal being measured. These kinds of things can be ignored in most cases, but in my case I had to go back redesign an enclosure and part of a PCB due to not taking these effects in account.

yungman

We mostly use the bath for high vacuum components. We kind of taking advantage that of the situation and use it. Now is almost impossible to buy those freon anymore because of the pollution.

yungman

Just a wild hunch, put a temporary spacer ( like a piece of cardboard) under the relay when you solder to create a tiny gap between the pcb and the relay when you solder. Then remove the spacer after soldering. Now you have some day light between the relay and the board. With this, dirt, flux is not going to be trapped as easy and you can get the flux solvent in between and clean the flux or dirt.

yungman

It's the vibration. We deal a lot with that. that's where rigid coax and secure mounting come in play. In fact I was helping a person here on photo diode detector circuit. He had the photo diode mounted on a platform moved by stepper motor, he used cable to connect to the transimpedance amp mounted somewhere else. I had him move the whole transimpedance amp to the platform with the photo diode and solve the problem. Get as much gain on the rigid part before sending the signal down. Have the amp bud up to the detector to minimize the components that can pick up vibration. At that, it is not a guarantee.

Averagesupernova

Yungman, the final fix for the flux residue under the relay was in fact a spacer that did what you described. The vapors escaped during soldering and did not impregnate the plastic on the relay. As I remember it, once the relay was contaminated there was little that could be done to clean it up. It had become part of the plastic.