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How Can We Prevent Our 0201 Nozzles From Clogging?



How Can We Prevent Our 0201 Nozzles From Clogging?
We have a formula stencil that had the apertures enlarged to maintain volume while overprinting the ends to keep solder away from the 0201 nozzle. Phil Zarrow and Jim Hall, The Assembly Brothers, discuss this situation.
Board Talk
Board Talk is presented by Phil Zarrow and Jim Hall of ITM Consulting.
Process Troubleshooting, Failure Analysis, Process Audits, Process Set-up
CEM Selection/Qualification, SMT Training/Seminars, Legal Disputes
Phil Zarrow
Phil Zarrow
With over 35 years experience in PCB assembly, Phil is one of the leading experts in SMT process failure analysis. He has vast experience in SMT equipment, materials and processes.
Jim Hall
Jim Hall
A Lean Six-Sigma Master Blackbelt, Jim has a wealth of knowledge in soldering, thermal technology, equipment and process basics. He is a pioneer in the science of reflow.

Transcript


Phil
And welcome to Board Talk with Phil Zarrow and Jim Hall, The Assembly Brothers who by day go as ITM Consulting. We are here to help you solve, resolve or certainly learn more about your assembly processes, situations and all. We have an interesting one today, Jim.

This is from C.T. He says, we are assembling PCBAs containing 0201 components. We have a problem with solder paste getting in the 0201 pick and place nozzles and clogging them up. We have been using a 5 mil thick stencil with a 1:1 ratio on everything except the 0201 passives that have a 10% reduction. I believe what is happening is when the 0201 passives are in place the paste is squished out to the sides and gets on the pick and place nozzle.

Our stencil vendors recommend using the same aperture size but going to an 04 thick stencil. I am concerned about reducing the volume by 20%. Has anyone tried a formula stencil that had the apertures enlarged to maintain volume while overprinting the ends to keep solder away from the 0201 nozzle? Jim
Certainly, lots of people are successfully printing adequate paste for 0201 chip components with 4 mil stencils. The amount of area reduction, I don’t think you will have to go to overprinting with any kind of reasonable pad size.

C.T. is probably right. With a 5 mil stencil, even 10 mil area reduction, you may just be printing too much paste, more paste than you need. Not too much, but on the high side of what is acceptable. Certainly a 4 mil stencil should be no problem and you have that 10% reduction too which you can do away with. I don’t think that you will have to overprint to get adequate solder volume. But it is something that you will want to check out.

The feeling I have is that if you go to these really small chips they are very thin the nozzle has to be relatively large, almost the width of the body of the component so that there is a big enough hole in it to get enough vacuum to pick up the chip reliably. With these really small chips, you get some solder sucked up into the nozzle. That is inevitable. Isn’t it true that most current placement machine offerings specifically have nozzle cleaners?

Phil
Yes, Jim. This has become such a problem, not just from solder paste, clogging up nozzles that the pick and place manufacturers have a need to address this. What they do is a two-prong approach. One is while the chip tooling is waiting to be picked up on the board with the appropriate components some of these systems shoot a little air through to unclog it.

Then there is another phase where they have a cleaning station, where they are still using air through the various chuck tips to clean them out. This is probably done during set-up, when the chuck tips are otherwise sitting idle. I know that aspect is an option in a number of machines. Not just solder paste, but dust from the tape reel feeder has clogged up the tip tooling, or certainly the filters that are further down the line.

Do you remember a while back when one of the major causes of billboarding, when a component was on its side, as well as a contributor to tombstoning was wearing pick-up tooling on the pick and place machine? The durability of the tips they are using now that is really seldom the problem it is more clogged. You see clogged tips contributing to billboarding and tombstoning.

Jim
The root cause, as with so many problems, is that everything is getting smaller. The chips are getting smaller, so the nozzles have to get smaller. The hole in them is really small and it is much easier to clog it up with a piece of dust or a couple particles of solder paste.

Things that wouldn’t cause a clog with larger nozzles because the hole is big enough and they just got sucked on through. Now the hole is so small in the nozzle, that it is just that much easier to get plugged. The placement manufacturers are addressing the problem by providing nozzle cleaning techniques on the machines. C.T., I think you can get away with it.

The other question, with going to a formula stencil, I am confident that you can print adequate paste for your 0201s. But what about all your other parts on the board? You say that you aren’t using any area reduction on your other parts.

So now, when you go down, you don’t have any area reduction to eliminate when you go down to the 4 mil stencils. If you have some bigger parts, 50 mil pitch, bigger capacitors, whatever it might be is the formula stencil going to give you adequate paste? This is the dilemma that most people deal with because of the variety of parts on any given assembly. There are different volumes of solder paste required for the different types of components.

Phil
Right, and a number of different approaches to that, including step stencils which we have talked about on occasion. I guess another thing before you go too far off subject, you might want to play with some aperture reduction rather than a 1:1 across the board. But remember to always make sure that you abide by the aspect ratio rules when you do your reduction. You want to avoid those tall and narrow apertures.

Jim
I think we have covered it. A lot of things could be involved. Needing to clean your nozzles may be a reality.

Phil
Obviously, if you are using a pick and place machine that doesn’t have this particular methodology you may want to look at doing it manually, doing pressed air type setup. I’m sure your pick and place manufacturer can give you some advice on handling a particular tool in that regard.

This is Jim and Phil, the Assembly Brothers. Hopefully we have solved C.T.’s question there or certainly gave him more to scratch his head about. We want to thank you for listening to Board Talk and whatever you do, whether your nozzle is clogged or not, please don’t solder like my brother.

Jim
And don’t solder like my brother. Please.

Comments

Mr. Mahilum was close... Sounds like the placement machine is not current enough to place the smaller parts. Almost all machines that are component capable below 0403 use a blow-off technique where the smaller components are actually blown off the end of the nozzle since the opening in the nozzles are so small and the components are so fragile. the nozzle slows once it is ~.05mill of the surface f the bard and then the paste height is sensed and the component is blown off in to the paste at ~.001mil from the surface.
Ike Sedberry, ISEDS
I have maintained a 3 mil stencil thickness for 0201 devices for the last few years. I definitely recommend it.
For your nozzles clogging, I would make sure you are using the right size. Talk to your equipment manufacturers process group. They will tell you what is the best nozzle for a 0201 package. Also, look at you nozzle maintenance. Do you have a regularly scheduled program for cleaning? If they start clean they are more likely to stay clean.
Alan Woodford, NeoTech
With paste clogging in nozzle, it is highly possible that you have problem in the following;
  1. pick up centering - it is more likely that your nozzle is not on the center of component.
  2. Choose the correct nozzle size - if utilizing bigger nozzle, big chance also to adhere on tip, then clog to nozzle and filter. if have paste on tip, component can be mounted to next sequence.
  3. mount offset - if you have mount offset, your nozzle can adhere to paste also.

I'm ok with analysis that there is more paste, if it will squeeze out, there is no problem if your nozzle size is correct, center to component during pick-up, and mount to correct coordinate (center, between two pcb pad).

Gregorio Mahilum Jr

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