How can I find a 1 um size vacancy under 150 um brass?

[rain2air]

I have soldered a pair of brass tape on the both side of a copper tape.
The thickness of each metal tape is about 150 um(micrometer).
The thickness of solder is about 2~20 um.
I want to know what device can find the small vacancy of solder between the brass and the copper tape.

 

[Nidum]

Depends on the area of the void . Very small voids will be difficult to detect by any method but larger voids that occur in normal soldered joints can be detected by a variety of standard NDT procedures . X ray and ultrasound detection are commonly used .

With these very thin layers you might be able to locate larger voids by measuring the through thickness electrical resistance at numerous points and detecting local variations .

 

[CWatters]

Curious to know why you need to know if there is a 1u void? Presumably it makes a difference to some something? so can you use that "something" to help locate it?

 

[Baluncore]

You should be able to use acoustic time domain reflectometry, or an ultrasonic thickness gauge. There will be a significant reflection from the acoustic impedance mismatch where there is air between the laminated metals.

 

[rain2air]

Curious to know why you need to know if there is a 1u void? Presumably it makes a difference to some something? so can you use that "something" to help locate it?

I want to prevent the void from being created in the solder.

 

[rbelli1]

I want to prevent the void from being created in the solder.

Why does it matter? What will the void do? CWatters asked because if your application is X and you will get Y problem then in your test setup you could do a bit of X and try to detect Y. If you see a bit of Y then you have the void. That may not be true of your application but if it is then you have a good way of measuring it.

BoB