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Trends for Printing Ultra Miniature Chips



Trends for Printing Ultra Miniature Chips
A reader wonders about the current trends and practices for printing ultra-miniature chips, a la 01005. Seeking advice, they have contacted Board Talk. The Assembly Brothers, Phil and Jim, take a look and share their opinions offering insight and advice.
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 Jim Hall and Phil Zarrow of ITM Consulting, the Assembly Brothers, coming to you from the ITM elegante ballroom high atop Mount Rialto. And we are here to talk about electronic assembly, materials, equipment, components, practices and procedures and who knows what else. A myriad of things. A wonderment of our wonderful industry.

Jim, what is today's question?

Jim
Well, it comes from B.L. He says, what are the current trends and practices for printing ultra-miniature chips, a la 01 005?

Phil
Ah, well somebody is heading into stormy waters there. But fortunately there is quite a bit of work going on in this direction and it really runs a whole range of things.

I guess some of the direction we have seen for a while in general was a trend going to smaller particle size, with regard to the solder paste itself, typically going to a type 4 paste. Type 3 paste just kinds of runs out of steam.

And of course when you look at the appropriate apertures and you apply the five ball rule you can see where this kind of goes mathematically. And then the other area of course that is brought up in terms is stencil thickness.

Wow, if you are still using a five mil stencil and you are trying to do these, general wisdom says you may be running out of steam. We've seen studies where some of the best results, and this is even going back a few years here, have been with a type 4 paste and a 3 mil stencil and for the best release and coverage. But Jim, there is a lot of direction to go.

Jim
Well certainly from a traditional area ratio for stencil apertures of .66, the 3 mil stencil gives you a lot better chance of getting there, because it is thinner. And I think we have to realize that a lot of the published research is being driven by people who are building handheld devices.

They are the principle users, the first users, and people who use these ultra-miniature chips more than anybody else. They have the reality where everything, take a smartphone, everything on the board is ultra-fine pitch. So a 3 mil stencil is a possibility.

Because you don't have issues with bigger components, where you need a thicker deposit of solder paste. On the other hand, other industries such as automotive and so forth, where they have a bigger variety of components are looking to try to stay with their thicker stencils and still print for these.

There have been some pretty heroic tests published with, I will have to admit, ultra-optimized printing equipment and processes that have successfully used a 5 mil stencil and a type 3 paste. But what capabilities you have, in terms of the age of your equipment, does it have all of the latest and greatest features on it for accuracy squeegee control and so forth.

What is the mix on your board? Do you need to continue to use thicker stencils? Those are going to drive your decisions.

Obviously, using a thinner stencil and a finer pitch powder is going to make the printing job easier. Can you do it with a more difficult combination? Yes. What is the degree of difficulty?

It is practical for you in your environment? That is something you are going to have to decide for yourselves.

Phil
Right and your level of expertise of your people and your environment. Because it is one thing to have a bunch of printing experts and that is all they do all day, live and breathe in a lab environment. And that is a lot different than the people you may have on your engineering staff and on your shop floor.

Jim
It may be different. They may have really good people.

Phil
There are good people out there. There's a few. Anyway, very good. Well, you've been listening to Board Talk. And remember, if you can't laugh at yourself we certainly we. And whatever you do...

Jim
Don't solder like my brother.

Phil
And don't solder like my brother, please.

Comments

One solution for handling the larger components is to utilize dispensing capabilities on board the printer. This allows you to optimize the stencil design for the smaller components and supplement areas where additional paste volume is required on the bigger devices. Additionally, more is being written about the importance of calibrating the printer regularly. This is often overlooked. The ease and speed of printer calibration should be considered as it is a significant differentiator among manufacturers and critical for optimized print performance.
Mark Brawley, Speedprint Technology
Interesting subject here. We have been printing type 5-7 pastes through 1-2 mil stencil for quite some time. We do a lot of chip scale packaging where we have to print very small features. Currently we have printed 30 micron features. I would try 3 mil stencil with a type 5-7 paste like others have suggested. Then if you need smaller, migrate down to a 2 mil or even 1 mil electroform stencil. We actually bump entire wafers this way and have used the same techniques to print on pads of substrates of SIPs using 0201 components. It really isn't as bad as it seems.
Fred Haring, NDSU RCA
It is important to make efforts to perform your own testing with regards to 01005 parts using your equipment, your stencils, and your processes. As Phil and Jim stated, lab testing can only go so far. You, as a user, must establish your ability to print and process these components.

You can buy testing boards or create your own. Be sure you match plating and board finishes. If you create your own baords (highly recommended) obtain those boards from your production supplier (if possible). Contact your paste supplier for guidance/assistance. Run more than a few test boards and use the resultant data to establish your internal processes and DfM rules.

John Burris, Automated Logic / Carrier Corporation
You guys would be great on NPR! I'm excited to hear the sounds callers attribute to there malfunctioning printers
Zack, MIT

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