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Paste printing, acceptable tolerance ?

Views: 1804

#41811

Paste printing, acceptable tolerance ? | 25 May, 2006

Having an issue with our paste inspector (human type).

Were printing paste on .5mm pitch pads (MLF package).

My question is - What is the acceptable print deviation (percentage) off the pad before you see problems after reflow?

0%? 1%? 10%? 25%? 50%? 75%? more?

I know, I know...... get a machine that will print perfect. Problem solved. This is an unacceptable answer.

Thanks for your input.

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RDR

#41812

Paste printing, acceptable tolerance ? | 25 May, 2006

How accurate is your placement machine? if it is accurate I would eval up to 25% off pad. the problem I might think you will have is errant paste or balls causing shorts if it doesn't coalesce completely.

Bottom line is, if the board is good at the end of the oven then it doesn't matter what it started out as.

Russ

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Chunks

#41823

Paste printing, acceptable tolerance ? | 26 May, 2006

This could be what we call a "non-problem". If your print is off slightly, yet after reflow there is no solder related defects, it should be considered OK. Move your inspector from the printer to right after the oven. This would enable them to inspect the entire process instead of just the screen printer too.

As for the percentage a print can be off is mostly determined by the direction it is off, pad dimension and mask outline of your board and placement of the part.

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#41827

Paste printing, acceptable tolerance ? | 26 May, 2006

This question cannot really be answered definitively here. There are unknowns such as your board design and solder land finish. I suggest you conduct a DoE (Design of Experiments) to determine paste print deposition X-Y-Theta tolerance for your applications. Opinions posted here should be a guide. A DoE will define for all in your organization.

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#41832

Paste printing, acceptable tolerance ? | 26 May, 2006

Paul,

The paste you use is another variable. As Pete recommends to know the real answer you need a DoE.

Jerry

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#41835

Paste printing, acceptable tolerance ? | 26 May, 2006

You also want to look at whether or not you are using lead free paste. "Typically" for leaded paste, 25% is acceptable, depending on end result, but lead free is less forgiving.Not only for the paste to migrate back to pad but also for comp. to right themselves. All answers given are pretty much correct, but personally it sounds like your inspector is a little anal.

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#41836

Paste printing, acceptable tolerance ? | 26 May, 2006

Thanks for the inputs. No time for DOE's (you know the drill). I need to get this inspector off my arss. I'm gonna give the inspector Russ's 25% answer AND his e-mail address !!!! LOL

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Chunks

#41840

Paste printing, acceptable tolerance ? | 26 May, 2006

Tell your inspector you are PURPOSELY printing 25% off to attain a synergistic energy level that will initiate the description of the criteria for requirements by developing a framework for the application architecture consistent with the planning corridor specified in our strategic initiative. Once bilateral goals are established, the engineer continues to undertake reinvention activities and new initiatives, we recognize the need to establish a framework to provide the necessary structure for optimal interactions and complementarily of the various reinvention activities. The framework delineates four major goals for reinvention: (1) maximize scientific opportunities through optimal use of resources; (2) enhance engineering interactions with the scientific community; (3) clarify and streamline decision-making processes; and (4) focus internal operations on outcomes and results. Each of these goals are further developed into specific reinvention objectives, and the plan is to use these goals and objectives as guide-posts as the engineer moves forward with the myriad of reinvention projects.

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#41844

Paste printing, acceptable tolerance ? | 26 May, 2006

Chunks,

ROTFLMAO !!!!!!

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#41845

Paste printing, acceptable tolerance ? | 26 May, 2006

CHUNKS! ROFLMAO also! Tarnations! I just love those seven dollar words! I wonder how many Euros that is. Jay

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#41895

Paste printing, acceptable tolerance ? | 30 May, 2006

I can't believe I waited 4 days to read this. Freakin' brilliant!

SMTGCE's got nuthin' on you, dude.

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#41896

Paste printing, acceptable tolerance ? | 30 May, 2006

Do a dirty DoE...print ten boards with the worst error you think you can accept, build them up, and count print related defects. At the same time, print ten spot-on and proceed the same. If you don't have any more defects on the off-print batch show him the data (hell, make it up ahead of time!) he can go pound sand!

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Bolos

#42014

Paste printing, acceptable tolerance ? | 7 June, 2006

first: what is your problem after reflow? second: a good rule of thumb is a tolerance of 1 mil. for example..if you got 5 thou stencil thickness then your range of thickness is 6-/+1 thou.. then you just improve after you get your height data and analyzed it through xbar r-chart..cheers..

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Reflow Oven

pcb components X-ray inspection