Release difficult from thick stencil

Maybe someone has a good explanation for this, but I'm wondering why your customer would dictate the equipment you use in your process. I thought typically contracts define the quality standards and you decide how to get there....show's you what I know about contract manufacturing.

Anyway, if you're trying to print on lands any smaller than 18 mils with that kind of sheet metal you're at risk of paste release problems. The rule of thumb I use (and seems to be the norm, based on the scads of papers and posts on this topic) is a 1.5/1 aspect ratio between land width and aperture width.

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Sorry,I can't help you with your problem, but would it be possible for your customer to take a little time to explain the reasoning behind their demands? I am sure we would all like to know. What are you putting on these massive deposits? Trends in both PTH & SMD are leading to less & less solder, not more. Good luck with difficult customer.

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In response to your questions: * Will a polyurethane squeegee blade help? NO * Will a Pro-Flow head help? NO, but it might be a cool excuse to buy one. Unfortunately, you will look like a jerk, if you talk your boss into buying one and then he /she finds out that it doesn�t work.

Wister there�s too much surface area on the walls of your apertures and that prevents proper release of the solder paste. The approach you take to squeegee work will do nothing to affect that problem.

The problem you have is that your stencil is twice as thick as you normally would make it. So in order to deposit the same amount of paste as you would with a thinner stencil, you need to pinch your apertures to maintain the same volume relationship on the inside of your aperture. When you do that, you ruin the aspect and area ratios [check the SMTnet Archives] necessary for good paste release. As you have noticed that these numbers are so blanked-up by using a thick stencil that polishing doesn�t do blank.

Here�s some things to try: 1 Try a Type 5 paste. This is a dumb idea, but it just may allow you to avoid doing what you should do, which is #3 below. 2 Increase your printer separation speed. This is a dumb idea, but it just may allow you to avoid doing what you should do, which is #3 below. 3 Sit down with your customer, explain the problem, and request that they either * Pay for the additional cost of using the thick stencil ... OR * Get the blank otta the way and let you do yer blankin� job!!!

Your important customer is a jerk!!! [And unfortunately you have to deal with it] Your customer should describe to you the quality and performance of the product that they expect your to deliver and not interfere with your ability to deliver product. It took many years for the US military to realize that by prescribing both process and quality requirements, they were creating an untenable situation for their suppliers [but then again that appears to be the purpose of rule making bureaucracies]

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Wister,

I agree with the other comments as far as challenging the customer, and minding proper height/width or better yet area aspect ratios. Let's assume you need to go with a .012" stencil for arguments sake. Talk to your stencil supplier about how aggressive they can be with the stencil wall angle. While there is the natural trapezoidal angle from laser cutting that is slight, there are also processes to exaggerate that angle and thus reduce your effective paste contact with stencil walls. For kicks and giggles you could also nickel plate the stencil for improved paste release characteristics. Good luck.

Steve A

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Is it possible you could simply over print to achieve the same paste volume? Supply me the numbers and I will do the calculation for you.

Cheers

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