Removing bubble from 200um holes via excitation 3

[AndrewUK]

Hi I’m working on removing bubbles form holes !after some thoughts and ideas,


We manufacture printed circuit boards, we drill hole 0.2mm deep , 0.2mm diameter and are blind (not fully through)
These holes are then treated in electroless copper to make them a conductive passage.

The circuits are held in the vertical plane, thus the holes are horizontal when submerged in the electroless copper liquid.

The problem is that the electroless copper (in liquid form) does not get in al the holes due to bubble entrapment.
Bubbles could be air from the atmosphere before being submerged and/or from the hydrogen produced during the
Electroless process.


I’m currently setting up some experiments to gather data, I’m looking at vibrating the jig that holds the circuits changing the following, Direction, Amplitude, Frequency

Does any one have any ideas on this?

I’m also looking at other techniques such at pluses in the liquid. If any one has any info on this please let me know.

do you think cavatation be a factor?

Could you treat the bubbles as a solid object and transport out as you would transport a component on a production line?

I'm thinking larger bubbles be easier to remove than smaller bubbles? (larger surface area, lower pressure).

I will post results of experiments soon

 

[Hatch]

How about doing it the other way. Ultrasonic cleaners excite the liquid so it cleans parts thoroughly. Maybe you can apply an untrasonic exicter to the tank so that the liquid will flow into the voids better and bubbles might be dislodged at the same time.

 

[AndrewUK]

maybe be, I was looking at inductors and did some test but these circuits are in panel form 20" x 21" with holes spread over the surface and blind from both sides. hence set up for good flow is hard. We have some side to side agaition on the jogs already.

But I will look in the ultra-sonic cleaners, will have to look into that would that be a Chaotic type of motion.

 

[GregLocock]

We used ultrasonics + vacuum in a similar situation.

What do you mean by pluses? oh , pulses?

Can you cook them a bit - the expansion of the air might encourage the bubbles to migrate.

What sort of failure rate do you get? If your yield is >50% (say) then it might be worth running a DOE on your existing setup to optimise the process.



Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[MikeHalloran]

That panel would require a pretty big ultrasonic tank.

It might be sufficient to just introduce the electroless liquid while under vacuum.

It would also probably be helpful to ensure that the holes are squeaky- clean and free of oil (e.g. coolant, preservative, lubricant from the drills) before starting the electroless process.



Mike Halloran
Pembroke Pines, FL, USA

 

[AndrewUK]

Firstly thanks for the ideas, all good ideas.

Sorry I meant pulse.


I forget to mention a critical factor; the panels are processed in a rack and as such are in rack approx 30mm held vertically , 10 panels in a rack (much like a toast rack). Hence this questions the uses of fluid movement to remove the bubbles.

As for hole condition all holes are high pressure rinsed and then cleaned with a chemical desmear which ‘etchs’ back slightly the laminate in the hole ensuring a good surface .
No coolant used.

The original vibration was air vibration. The motor was of the shuttle type acting the vertical plane. I changed to electrical rotary vibration (motors are mounted with masses rotating in the horizontal plane). This has had an effect on reducing the bubble entrapment. Which lead me to think that I really should quantify this.

Invertors on order so I can change frequency of vibration, I think this may have more of an effect than amplitude.

Any ideas on type of vibration to ‘transport’ bubbles along roof of hole?

Can you post photos on here? Would be easier to show some details.