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Stencil life

Views: 3299

#80275

Stencil life | 19 April, 2018

Hello experts,

what would you recommend as a standard practice for stencil replacement? I am having here a stencil from 2004 that is worn out enough and has a small dent on the image, but still have to prove why I want to change it.

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dwl

#80276

Stencil life | 19 April, 2018

When your stencil foil looks like cooked bacon it's time to replace it.

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#80284

Stencil life | 20 April, 2018

We usually replace stencil when we start to get problems with the solder paste printing i.e. uneven solder paste deposit etc. Until then it doesn't matter how many years ago it's manufactured, but how many prints it passes and if the operators didn't do something silly with it.

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#80286

Stencil life | 20 April, 2018

Show that it is cheaper to replace than to make bad boards that need rework. Surely you can get QC to complain about the boards pasted with that stencil.

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#80513

Stencil life | 7 June, 2018

Hello, the colleagues are all right. What I did in addition to show customers and quality that we either need or dont need a stencil: 1. Made a procedure - in there i defined 50 000 cycles and then the stencil has to be checked by me. In the checks if you have dents on the image, rust, signs of delamination from frame (if you use frames). I also got a special tool to measure the tension of the stencil to see if it is ok. 2. Made a special check list in where i check all that, input the tension results from the 4 corners and the middle 3. Get information from SPI (cpk, trends, defects). If spi is giving bad panels because of stencil - immediate change. 4. If everything is okay - 50000 more cycles or until SPI signals way too many defects. Keep all check lists :) Oh yeah i forgot - we had traceability system to count cycles and automatically stop production at 50k. Then only i can release it back to production. If you have any more questions feel free to contact me.

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#80902

Stencil life | 16 August, 2018

Hey man, can you please suggest what you do for traceability system to count cycles of the stencil. Is there any special setup for that or just a Excel sheet with formulas.?

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#80903

Stencil life | 16 August, 2018

Never heard of any traceability requirements for stencil cycles.

The SPI machine should be the judge of how your print process is performing.

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#80907

Stencil life | 17 August, 2018

Traceability can be made for many things. It is up to the factory and what it wants to implement. You can have traceability on the stencil for a several reasons: 1. Want to check stencil cycles 2. Want to verify if stencil is the correct one loaded 3. Want to have a history of when the stencil was cleaned and by whom. 4. Want to have an automatic stop of the line for example if stencil was used more than 8 hours on the line. Then maybe you have to clean it or put in a spare one. It is very interesting approach to have that, but also requires a lot of efforts to realize it.

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#80909

Stencil life | 17 August, 2018

Correct stencil, wiping frequency effectiveness,and correct paste deposition are all verified by the SPI machine.

I suppose you can put all kinds of things in place, but you may want to determine what is practical and "why?" are you doing it.

Traceability requirements are typically set by the customer not the factory in my experience. Anytime you say "traceable" there is cost incurred.(sometimes significant) At the end of the day you need to determine the value of all these checks and data collection. If it is not a customer requirement you are paying for it.

Just a thought......

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#80910

Stencil life | 17 August, 2018

I agree with you. I just said, if it is customer requirement, factory has to implement it, right? :) Of course it is huge amount of money. SPI is the main control, but it doesnt save you the pressure, speed, snap of from the printer to the trace (usually). For example, the traceability that we use has that information on every panel (pressure, speed etc), but not so much for the stencil information. Another company that I saw had more information stored from the stencil. Its all depending on customer-company relationship. Another example: of course the SPI will catch that you have the wrong stencil, but in that case you already have at least 2 panels which are printed and have to be scrapped(assuming you dont clean them). If you verify the stencil before that, you wont have that scrap.

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#80939

Stencil life | 22 August, 2018

If we don't take SPI machine is given in the equation, another control should be put in place. Buckcho your approach is interesting, but requires a lot of effort. Do you guys think the stencil printer can count the prints for the same program? Or even better have the option to scan the stencil towards this count of prints? I have DEKs - Horizon Regards, Emil

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#80941

Stencil life | 22 August, 2018

I have the same machines, haven't figured it out yet. Only idea i got is to scan every batch and get a rough number of the prints. For example if you have an order of 500 panels, usually it would take 500prints to produce them (maybe 4-5 differences depending on various reasons) Again, this would require a programmer. Maybe it can be done with excel: scan stencil (if you have barcode, or input manually), scan order (or input manually numbers) and it counts all orders. Then conditional format if the count exceeds 50 000 prints - then stencil becomes red. This is the simplest i could think of.

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