|Ask the Experts|
July 7, 2020
0201 Pick & Place Nozzle Plugging
We are assembling PCBA's containing 0201 passive components. We have a problem with solder paste getting in the 0201 P&P nozzles and plugging them up. We have been using a .005" thick stencil and with a 1 to 1 ratio on everything except the 0201 passives that have a 10% reduction. I believe what is happening is when the 0201 passives are placed, the paste is squished out to the sides and gets on the P&P nozzles.
Our stencil vendor is recommending using the same aperture size but going to a .004" think stencil. I am concerned about reducing the volume by 20%. Has anyone tried a 4 mil stencil that had the apertures enlarged to maintain volume while overprinting the ends to keep solder away from the 0201 nozzles?
|Expert Panel Responses|
Perhaps adjusting the Z height of the placement would be the easiest thing to do. Set it little bit higher so that it does not press the 0201 as deep in to the paste deposit.
.004" thick stencils are used all day everyday all over the world for PCB assemblies containing 0201s. A .004" thick stencil should provide adequate paste volume for 0201s.
Technical Support Engineer
I would not go right to the .004" stencil since this is reducing globally. I would actually go to a home plate style aperture for 0201 parts. To me the bigger issue sounds like the pick and place is actually driving down too far for placement.
I would check component height in the part data, or check stand offs and make sure they are not to high causing you to overdrive into the paste. A 20% reduction in pad solder coverage seems extreme to me also. If you are at 10% and seeing proper fillets post reflow solder paste is not the issue.
First, you are correct that you should carefully consider the transition to a 0.004" stencil. There will be an impact to other components, but perhaps not the components you might think. For many apertures, the reduction in thickness may be partly, or even fully offset by an increase in transfer efficiency, and your volume may not change nearly as much as you think. It may even increase for some apertures. The main impact will be for very large apertures, where there is some scooping going on.
Second, do consider alternate explanations for the plugging. For example, how often to you catch missing 0201 components later in the process? If you occasionally lose a part between inspection after pick and placement, you may stick the nozzle directly in the paste. It doesn't take many occurrences of this issue to plug up nozzles. Also look at what is the required placement force for the 0201 components, and whether optimizing the placement force may alleviate the issue, if it is truly due to squish-out.
The Tozai Nozzle Cleaner, sold by Juki in the Americas, can remove all solder paste residue, even from 0201 and 01005 nozzles. Tooling is available for all styles of nozzles from all major placement manufacturers.
North America Sales Manager
It's quite possible that the .004" thick (100 micron) will have higher print transfer efficiency and leave as much or more paste. If one assumes the area of the pads is .28 x .3 (from a resistor manufacturers data sheet, the area ratio of a .005" thick pad is 0.482. Going to a .004" thick stencil increases your area ratio to .724.
This will increase your transfer efficiency from below 50% to nearly 100% if you are using a state of the art solder paste.
Global Director of Customer Technical Support
Alpha Assembly Solutions
If you have paste getting squished out the sides high enough to get on the nozzle, you should have plenty of volume. You may want to make sure placement is where the nozzle is getting the paste.
Depending on the smt platform you have, it could be during a board level test area or tool bank on the machine contaminating the nozzle. If placement is the only source, you could try lower your placement force. Also make sure you are using the right size nozzle.
Manufacturing Applications Specialist
The 0201 and 01005 component pads pasting is definitely a challenge. My recommendation is to actually go to a 3 mil stencil and nano coating for sure. There are companies that are offering stencils that are high quality and can yield great results on small components paste deposition.
The other aspect on your problem is that you need to confirm 100% that the paste gets on the nozzle the way you've described it.
Engineering and Operations Management
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