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

[royzizzle]

I want to build a EEG and the site tells me to buy a PCB from some manufacturer. Will my product have competent performance if built with breadboard?

What is so special about PCB？

 

[yungman]

It all depends, for RF, it is most likely not the same, for high impedance circuit, it likely not the same. For run of the mill circuit that is a few hundred KHz, impedance in 100KΩ or below, it is likely the bread board is close to the pcb.

Circuit layout is very important. This is one thing school don't teach you. You learn signal but you thing everything just magically going to the ground and is all good. In real life, ground is the second half of the circuit and it is just as critical. If you know grounding, circuit is just that simple, the circuit in the textbooks usually work. The devil is all in the detail, that's where people lost the war.

Also, wires in breadboard are much more susceptible to EM noise pickup as they hang in the air.

That said, there are different ways of bread boarding also. For example, for high speed circuit, we use ground plane board and "dead bug" the IC or transistors. You can get to a few hundred MHz with bread board, but it gets harder and harder to do. Now a days, making a run of pcb is a lot cheaper than 20 years ago. I have a few circuits that it's just too much trouble to build for demo, I am actually laying a pcb and combine a few of them on one layout. I did some inquiry on ebay from pcb house in Hong Kong, for 4 layer 30cmX30cm panel, it's only about $200 a run. I love to do it in USA, it's easy to say than to do. I got a rough quote from a friend, the same run would be close to $700. It is easy for people that don't pay from their pocket to say keep the job in America. But it it is your money and there is a bid difference in price...

 

[Averagesupernova]

It will also depend on the current involved. The breadboard will typically have more resistance on connections than a soldered up tidy PCB.

 

[Mike_In_Plano]

These biomedical circuits have a lot of gain, but little bandwidth. Hopefully, you're not intending to tie it into an AC connected device - few are rated for patient connection.

That said, yes, you can use breadboard techniques - if you're neat and thoughtful. By using a 1/4" strip of copper as a local ground, you can get fair performance from the front end amplifier.

 

[the_emi_guy]

Depending on the nature of the circuit it can go both ways ...

Most circuits are more well behaved when they are hugging a nice solid ground plane on a PCB (nice low Z return paths, low crosstalk ...).

Certain analog circuits (oscillators, op-amp circuits) have been known to work beautifully hanging in the free air, then fail miserably when hugging ground plane after implementation onto a real PCB (parasitic capacitance).

Of course we want that nice solid ground plane in all cases, but need to manage parasitic capacitance on a case by case basis (clearing plane under certain pins of certain parts).

 

[yungman]

Don't forget one most import thing, if your ultimate goal is to put the circuit on the pcb, doing the first try on pcb get you much closer to the final product, less surprise. As I said, a run of pcb is not that expensive. You can layout with spare circuits that you can try. When I do a proto pcb, I put in more poles and zeros compensations than necessary, I don't have to stuff it if I don't need it. By careful planning, you can put in a lot of "hooks" so you can experiment even with a pcb.

 

[gnurf]

What is so special about PCB？

In addition to what has already been mentioned, I'd add reduced size as a reason to use a PCB (using SMT) over a breadboard.

Certain analog circuits (oscillators, op-amp circuits) have been known to work beautifully hanging in the free air, then fail miserably when hugging ground plane after implementation onto a real PCB (parasitic capacitance).

Of course we want that nice solid ground plane in all cases, but need to manage parasitic capacitance on a case by case basis (clearing plane under certain pins of certain parts).

Do you by any chance have an example schematic of a circuit that is so sensitive that even the capacitance (a few pF?) formed by a single pin and the underlying plane can be harmful? Thanks.

 

[Averagesupernova]

In addition to what has already been mentioned, I'd add reduced size as a reason to use a PCB (using SMT) over a breadboard.
Do you by any chance have an example schematic of a circuit that is so sensitive that even the capacitance (a few pF?) formed by a single pin and the underlying plane can be harmful? Thanks.

A place I used to work had the first LO in a measuring receiver air mounted. It was a negative resistance VCO that had a top end frequency of around 1200 Mhz. Placement of components would adjust it into range so the PLL would lock throughout the whole range. It was a pain to tweak those components position. I recall capacitor leads were coiled and the spacing of those coils would trim the oscillator enough to bring it into range. It used a couple of varactor diodes of course and if those leads were too long or too short it would not be able to be brought into range. A pain to calibrate but a much bigger pain to manufacture. It seemed to work very well once set up and had good stability over temperature and did what it was designed to do very well.

 

[yungman]

In addition to what has already been mentioned, I'd add reduced size as a reason to use a PCB (using SMT) over a breadboard.
Do you by any chance have an example schematic of a circuit that is so sensitive that even the capacitance (a few pF?) formed by a single pin and the underlying plane can be harmful? Thanks.

For transimpedance amp that can measure under a pA, the feedback resistor is like 10GΩ or more, one pF will make a day and night difference. Even for 1GΩ resistor, I had to cut out the ground plane around the junction and area close to the input.

Also, in microwave, 1pF is quite significant. At 1GHz, the reactance is only 159.23Ω! You tell me whether it is significant or not!

 

[gnurf]

A place I used to work [...]

Interesting story. I'm not sure coiling the capacitor leads would be the first thing that crossed my mind if such a setup failed! Until now anyway.

For transimpedance amp that can measure under a pA, the feedback resistor is like 10GΩ or more, one pF will make a day and night difference. Even for 1GΩ resistor, I had to cut out the ground plane around the junction and area close to the input.

Also, in microwave, 1pF is quite significant. At 1GHz, the reactance is only 159.23Ω! You tell me whether it is significant or not!

Yeah, that makes sense. I flipped through some transimpedance amplifier app notes and sure enough they recommended to remove nearby planes. I learned something, thanks.

 

[yungman]

Interesting story. I'm not sure coiling the capacitor leads would be the first thing that crossed my mind if such a setup failed! Until now anyway.
Yeah, that makes sense. I flipped through some transimpedance amplifier app notes and sure enough they recommended to remove nearby planes. I learned something, thanks.

You're welcome. Actually for 10G resistor, I don't even think pcb can do it. Not because of the capacitance, but the leakage on the surface due to moisture and dirt. We stand the input end on a teflon standoff. We use leaded op-amp and bend the -ve input pin out and solder onto the teflon standoff to the resistor.

 

[Averagesupernova]

Interesting story. I'm not sure coiling the capacitor leads would be the first thing that crossed my mind if such a setup failed!

The coiled capacitor leads were standard procedure. Every single one was built like that and the spacing between turns was adjusted to help bring it into range. It was part of the design.
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I can also recall a design for a DVM that was integral to another piece of equipment that stood several larger resistors on end to avoid leakage current instead of having one single resistor laying down on the PCB. One end of each resistor was soldered to the PCB and the other two ends were joined in mid-air. It worked.
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I also recall in similar DVM circuits having relays that switched taps on the main voltage divider on the input of the DVM. When the PCB went through the wave solder machine flux would get trapped under the relay and cause leakage. Now the input voltage divider no longer scaled the input correctly. A couple of volts off at 2000 volts was out of spec. Anyone care to guess how how we proved and tested for this besides just swapping out the relay?

 

[yungman]

Don't need to prove, I can attest that too many cases of leakage that totally ruin the circuit. You have to be careful even for a few MΩ resistor. We have a special freon bath to wash the pcb and then use condensation freon to rinse the board.

 

[Averagesupernova]

Actually yungman it does/did need to be proven. The residual flux was only a problem in humidity so the fix for it needed to be proven well since we had no idea what type of climate it would end up in. It really wasn't a problem in the plant.

 

[yungman]

Actually yungman it does/did need to be proven. The residual flux was only a problem in humidity so the fix for it needed to be proven well since we had no idea what type of climate it would end up in. It really wasn't a problem in the plant.

As I said, it depend on how high impedance. In my experience, some of the circuit will not work most of the time if you don't take precaution. Even through hole components, we washed a few times with flux cleaner and still it did not work. Try a 1GΩ resistor and you'll see.

 

[Averagesupernova]

As I said, it depend on how high impedance.

What you actually said was:

Don't need to prove,

And I'm not sure you are getting the point. So, forget it.

 

[yungman]

What you actually said was:



And I'm not sure you are getting the point. So, forget it.

You said anyone can guess how you prove it. I reply that you don't need to prove, I've seen too many cases already and I am fully support what you said about the flux.

 

[Averagesupernova]

Yungman I don't understand you. I accept your last post and will not argue that you have probably seen a lot 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:

Anyone care to guess how how we proved and tested for this besides just swapping out the relay?

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 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.

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.edu/projects/garbz2_prj.php
doing the iron-on transfer takes some practice

a Dremel with the drill pess accessory is really handy.
http://www.micromark.com/RS/SR/Product/83453_R.jpg

 

[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]

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.

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

Just breathing on the relay made the meter reading change.

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]

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

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]

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.

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.