crackling noise lifting a PCB after soldering components

Hi all,
I'm currently assembling a DR MQ5 equalizer.
The PCB is quite big.
When I gently lift it from the table, by holding the short edges with my fingers, I think I cause it to flex a little (you cannot see the bending, but it most probably bends a few tenth).
Since I've soldered all film capacitors (and some socket) on the PCB that lift movement causes a single faint "cling-ching" high-pitched noise. The noise is so low that I have difficulties in understanding from where it comes.

It sounds like it a sort of little loose metallic part, but the fact I can hear it by just gently lifting the PCB induces me thinking it is caused by the PCB bending.
In your opinion, does such noise comes from:
-the long and rigid film capacitors scraping their base against the PCB Surface when the PCB bends?
-by something inside those capacitors that is moved by the soldered legs when the PCB bends?

I'm wondering if it is something the more experts of you have ever whithenessed and if I shall consider it as not being a problem.

Thanks.

Bear in mind that your board is completely unscreened while out on the bench , small currents might flow while its in contact with the bench , all of a sudden you lift it those leakages currents change ,that could be what your hearing , its not unusual to hear small clicks  or static fuzz  type sounds in that situation in my experience .

Tubetec said:

Bear in mind that your board is completely unscreened while out on the bench , small currents might flow while its in contact with the bench , all of a sudden you lift it those leakages currents change ,that could be what your hearing , its not unusual to hear small clicks  or static fuzz  type sounds in that situation in my experience .

Click to expand...

Thanks for the reply.
However the PCB is still not complete therefore not connected to any power/audio signal.

I'm talking about a mechanical noise not an audio noise.

It iIs like if some of the film capacitors have a metallic loose (loose = that could be forced in someway to scratch against something else) little part inside and putting some strain on their soldered legs makes the part to emit a very very low mechanical "cling".
The stain is provided by lifting the PCB (i.e. causing the PCB to flex).

For this reason I was asking if someone who ever opened (or knows how they are inside) such type of capacitor may confirm that the noise is nothing to be scared of.

I hope to have clarified the topic.

Ahhh I see ,
On one ocassion I got a passive P.A. speaker in for repair, fault no sound from the tweeter. Tested the tweeter ,continuity across the voice coil was good ,in the end it turned out the series  foil capacitor on the high pass section of the crossover was open circuit ,physically it looked perfect but maybe vibration had caused the internal connection to fail . Its the one and only time I saw a fault like this ,I suspect that its more likely to happen on an axial mounting style cap than a radial type . If a close physical inspection of the solder joints and components shows up nothing ,continue with the build and see if it passes signal in the end .

Tubetec said:

Ahhh I see ,
On one ocassion I got a passive P.A. speaker in for repair, fault no sound from the tweeter. Tested the tweeter ,continuity across the voice coil was good ,in the end it turned out the series  foil capacitor on the high pass section of the crossover was open circuit ,physically it looked perfect but maybe vibration had caused the internal connection to fail . Its the one and only time I saw a fault like this ,I suspect that its more likely to happen on an axial mounting style cap than a radial type . If a close physical inspection of the solder joints and components shows up nothing ,continue with the build and see if it passes signal in the end .

Click to expand...

No, solder joints are all carefully inspected and look fine.
I really think the sound is caused by the capacitor legs that transfer the bending movement to the metal foils.

        _______
        |______|
        |            |
==========   
^                        ^
force              force 


        _______
        |______|
        /          \
==========   

if you bend (we are talking about tenths) the PCB the soldered legs can either break or transfer the flex to the internal foils.
The metallized foils emit the sound.
You can barely hear it and it doesn't come always from the same capacitor.

Now, if this means that the capacitors have been damaged (e.g. because I've let them overheat while soldering) this I do not know. I fear I will discover it only when I'll complete the build.

Let's cross finger.

mudseason said:

No, solder joints are all carefully inspected and look fine.
I really think the sound is caused by the capacitor legs that transfer the bending movement to the metal foils.

        _______
        |______|
        |            |
==========   
^                        ^
force              force 


        _______
        |______|
        /          \
==========   

if you bend (we are talking about tenths) the PCB the soldered legs can either break or transfer the flex to the internal foils.
The metallized foils emit the sound.
You can barely hear it and it doesn't come always from the same capacitor.

Now, if this means that the capacitors have been damaged (e.g. because I've let them overheat while soldering) this I do not know. I fear I will discover it only when I'll complete the build.

Let's cross finger.

Click to expand...

component damage from soldering iron is very unlikely unless you really suck at it.
how long did the hot iron tip touch the pins? more than 1 minute? if only for a few seconds, then you should be fine.

always check if component orientation is correct.
always check if component value is correct.
always use a multimeter to check for continuity, shorted solder joints, cold solder joints, etc., instead of just powering up the circuit to see if it'll blow up or not.

Thanks for the suggestions.

metalb00b00 said:

how long did the hot iron tip touch the pins? more than 1 minute? if only for a few seconds, then you should be fine.

Click to expand...

few seconds

metalb00b00 said:

always check if component orientation is correct.
always check if component value is correct.

Click to expand...

I check before soldering on schematics and PCB overlay
I check after soldering again, and if available I also use reference pictures.

metalb00b00 said:

always use a multimeter to check for continuity, shorted solder joints, cold solder joints, etc., instead of just powering up the circuit to see if it'll blow up or not.

Click to expand...

When applicable I also use the multimeter, and I carefully inspect each joint after soldering and all joints after cleaning them.

I guess you do not have suggestions regarding my original question: the mechanical sound (very low "cling-cling" from metal film capacitor when I shake/move the PCB).

If so I do not see many other options than powering the stuff and see if it works, do you?

mudseason said:

When applicable I also use the multimeter, and I carefully inspect each joint after soldering and all joints after cleaning them.

I guess you do not have suggestions regarding my original question: the mechanical sound (very low "cling-cling" from metal film capacitor when I shake/move the PCB).

If so I do not see many other options than powering the stuff and see if it works, do you?

Click to expand...

you could pull the suspected caps out and check them with a multimeter, no?
it's not like all of them are making the same cling sound...

I have soldered many metalized film caps, from cheap epoxy potted mylar which crack easily to expensive ones, Wima and the likes; I can tell you for a fact no such cling sound ever been heard when I flipped a board multiple times.

metalb00b00 said:

you could pull the suspected caps out and check them with a multimeter, no?
it's not like all of them are making the same cling sound...

I have soldered many metalized film caps, from cheap epoxy potted mylar which crack easily to expensive ones, Wima and the likes; I can tell you for a fact no such cling sound ever been heard when I flipped a board multiple times.

Click to expand...

The point is I can hardly figure out which one is making the noise.
The "cling" is so low in volume that could come from any of them (there are around 40 of them soldered...)
If I had a stethoscope I would try with that...
but, it could be possible that the noise is not caused by the capacitors, may be it is caused by the IC sockets, or
may be is the PCB itself:  it is very long and when it bends a layer/foil could make the noise) ...

Something that I'm sure is that if I fix the PCB to the chassis I can still hear it BUT in a very limited way if I tilt the PCB.
to summarize is like if the noise (when tilting the PCB) is:
- emitted from 3 or 4 sources (not always from the same area/zone) when the PCB is free
- emitted from 1 source (not always from the same area/zone) when the PCB is fixed to the chassis
Is this because I limit its bending when fixing?

Thanks again.