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Capability Study for Solder Printing Process

Sophia

#2984

Capability Study for Solder Printing Process | 19 September, 2000

Hi guys,

I have been working in the SMT pick and place process for five years, and now I'm responsible for the solder paste printing process, and one thing that I notice is that the actual process that we have is to poor, actually our main defects are caused by this process, can somebody help me on what should I check to have a capability Study for this and the best tools to decrease the defects, like solder height, off location, stencil parameters, all the important things????

thanks in advance.

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#2985

Re: Capability Study for Solder Printing Process | 20 September, 2000

Congrats. You now control the source of almost 70% of the defects of your SMT operation.

There is a neat series of presentations on printing, each year at SMI. One of the best of the SMI series was in 1997, because presenters used a common board design, paste, stencil, etc when talking about the thirty-six or so variables that contribute to the quality of a print. The papers written by these presenters are: * "Characterizing And Controlling the SMT Screen Printing Process" MJ Beck, View Engineering * "The Affect Of Aperture Area Aspect Ratio On SMT Printing Technology" RS Clouthier, AMTX * "Importance Of Board Planarity" G Trinite, Elexsys International * "Solder Paste Design And Performance Verification For Fine Pitch Printing" RR Lathrop, Jr, Heraeus Cermalloy * "Optimum Printer Properties For Fine Pitch Printing" A Johnson, MPM

Further, I�d suggest that a moderately ambitious rep for the company that makes your screen printer should be able to give you copies of papers on printing that will give additional insight.

Finally, I was boggled yesterday when I received an advert from DEK (the printer people) googooing about their products. Their top of the line printer had a Cpk of 2. Mmmmm

Good luck

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#2986

Re: Capability Study for Solder Printing Process | 21 September, 2000

Once you know what your print should look like, means you have found the right apertures, stencil thickness, stencil finish and the right printer adjustments and alignments, the main things to watch for or better to control when printing is in progress are: - Paste condition - Cleanliness of PCBs and stencil - PCB alignment - Stability of the settings The "best tools" are well trained operators with profound knowledge to decide when a particular print does not meet your postulated criteria. That will work of course only when you have established a rework (cleaning) process for misprinted PCBs. The means you use for process control depend on your printer and inspection equipment but in the end it�s your operators jugdement abilities that count. To know what�s good and what�s bad and how to correct the bad is essential. Print height, alignment and cleanliness are good critera to control.

good luck

Wolfgang

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Mike Rowell

#2987

Re: Capability Study for Solder Printing Process | 21 September, 2000

Hello Sophia,

I am an applications engineer for Speedline/MPM. I'd be happy to help you with your questions. feel free to e-mail me or contact me at Speedline/MPM. There are many factors that could cause problems with the print process, I would prefer to discuss your process with you to help determine what steps you could take. 1-800-528-6001.

mike

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C.K.

#2988

Re: Capability Study for Solder Printing Process | 21 September, 2000

Dave:

That's just fine and dandy but where does one find these papers?????

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Sully

#2989

Re: Capability Study for Solder Printing Process | 21 September, 2000

I am interested in those papers, too. Any other help out there?

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Ricardo Fuentes

#2990

Re: Capability Study for Solder Printing Process | 21 September, 2000

I'm interested also to get those files or papers Thanx

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#2991

Re: Capability Study for Solder Printing Process | 21 September, 2000

Geesh, what a bunch of babies!!!

I've got two alternatives for ya: 1 SMTA sells the SMI proceedings 2 Authors / authors' companies often provide copies of papers to interested folk

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#2992

Re: Capability Study for Solder Printing Process | 21 September, 2000

Mike: Why not hold this conversation on-line, so that we can all benefit? That's really one of the purposes of forums like SMTnet ... free flow of information for the benefit of all. Not a place where sale-types can develop contacts. Right???

While I have your attention, why not volunteer to as the question responder in an up-coming OnBoard Forum?

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K.T

#2993

Re: Capability Study for Solder Printing Process | 22 September, 2000

I 100% agree with Wolfgang. No matter how many in line or off line inspection gadgets, zillion $ printers, and top of line stencils you use, bottom line is a properly trained machine operator who gives a rat about his/her job that makes the difference.

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Francois Racine

#2994

Re: Capability Study for Solder Printing Process | 23 September, 2000

Hi Sophia,

I`m responsible of SMT line and we solved this problem with a complete automatic solder paste printer machine. In the past we had problem with off alignment and solder height too.... at that time we used a semi-auto printer machine and we had problem of alignment. The reason is: when you work with PCB, the drilling process and the trace exposition are seperate...so....you can have a little offset between the SMT pad and your reference holes. If your solder paste printer use two reference holes in your PCB you have a tolerance for these holes so, you can have an offset in you printing specialy when you use fine pitch components. If you use a full automatic printer, your printer reference are now two fiducial marks on your PCB. With this process, your final result is more efficient because you don`t have to work with mechanical tolerances. For solder height, I suggest to use a 6 mils thick stencil for fine pitch and all other package. If you always use a 6 mils stencil, your aperture in your stencil must be at least 10% smaller of your SMT pad if you don`t want to find solder ball around your components. Finaly, if you always use a 6 mils thick stencil, it will be easy for your PCB Designer to use the good amount of paste for all components on each new project.

If you have other questions concerning the solder paste process, do not hesitate to ask them via this SMTnet forum.....

Good luck

Francois

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KirkS

#5032

Re: Capability Study for Solder Printing Process | 22 January, 2001

Hey Mike, what do you recommend for PCB cleaning if there was a mis-print during the screen printing process. Currently we are hand cleaning them with a SMT solution but are having problems with solder balls in the via's and joints. What cleaning material and or machines do you recommend.

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Verm

#5048

Re: Capability Study for Solder Printing Process | 23 January, 2001

Hi kirks, I don't want to appear to be selling a product for a particular supplier, but we recently (six months ago) purchased a Kerry SC1000 stencil / misprinted cleaning system. We too were experiencing solder beads in via holes left behind after cleaning by hand. The fundamentals of the machine are great, BUT, be very cautious about believing the spiel about running costs, material usage etc. They are alot higher than you are led to believe.

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rpereira

#5058

Re: Capability Study for Solder Printing Process | 23 January, 2001

I have recently completed a HUGE screen-printing DOE. I used Taguchi methodology and man I got good results!

Here is what I learned for what it's worth: (p.s. to the MPM apps guy I sent a copy to Tim Gillis, Lou Fuda, etc...)

EFab vs. Laser: EFab had better paste release characteristics (~10% more) Laser showed better variability (~3 db's or 29%) Note: Stencil company papers will differ, but trust me my results were consistent, and most importantly they confirmed during the final confirmation study.

4 mil stencils vs. 5 mil stencils: 4 mil had slightly better paste release variability was close

0.5 mm pitched CSP aperture geometries: Square and Square with rounded corners apertures were close ROUND IS TERRIBLE - DON'T USE THEM FOR small CSP applications

I did some stuff with the MPM parameters, to summarize the most critical factor was separation speed (Called Slow Snappoff on MPM):

FAST SEPARATION SPEED IS BEST, when you have good vacuum tooling to hold the PCB down, otherwise it will stick to the stencil...

Lastly, most papers are done under optimal conditions without manufacturing "noise". I love reading papers, but I usually don't believe anything until I test it myself!

Use papers as a starting point, but make your own decisions, after all it's your butt if it don't work!

GOOD LUCK! Screen printing is awesome!

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