Good stencils and optimising printing (JLCPCB / Alpha / Tannlin)

[loki42]

I'm attempting to optimise my printing process. Do people find a performance difference between Alpha, Tannlin and cheaper stencils like JLCPCB? How about coatings? Do you tell your stencil provider what paste your using? Do you get them to optimise apertures based on your paste choice?

I've got a Koh Young SPI on the way so hopefully this will give me more info on print quality but I'm wondering if there's easy improvements. Is there a decent low cost (chinese?) ultrasonic stencil cleaner?

[Rat_Patrol]

For manual paste work, I honestly settled on JLCPCB frame-less stencils and cut them a bit to fit in my Neoden manual stencil machine. I've been happy with the etched stencils from JLCPCB, but be sure to get file confirmation so they get everything right if you need anything special.

The Euro Circuits stencil machine/system looks great, I may look into that, but the boards have to be made for the system to work right.

[loki42]

Have you tried higher end brands and compared? I'm mostly wondering about consistency of solder release and wipe frequency etc.

I'm using 29" framed stencils in an MPM printer. 

[SMTech]

I certainly think the JLC/PCBWay foil material is very different to the foil used by the higher end stencil  manufacturers. The squeegee sounds different moving across it, like the finish is rougher. I think the paste release is poorer, especially the cheap ones and while I have 20 year old framed stencils form Alpha, I don't see the Chinese ones ever lasting that long. Tecan foil even has a ripple in the finish they say helps with the solder roll and they also offer squeegees in Nickel, which for hand printing felt nice and smooth but was also easy to damage.

You can get handheld ultrasonic stencil cleaners, here's a UK offering https://www.gen3systems.com/gensonic-stencil-cleaner I have done googling before there are others globally but they are not easy to find (https://seikausa.com/electronics-mfg-equipment/quality-assurance-products/sawa-ultrasonic-portable-stencil-cleaners/sc-500he-hand-held) . This process is a HUGE improvement over trying to do it with gallons of spray on cleaner and wiping. However you need to apply more than you might think. You can mock this process by using a shitty laundry one off Aliexpress, it won't last long but it was an interesting experiment. The Gen3 is £1300 or so in the UK it even has a direct rival in a slightly different color. I'm told some people use this inside the printer to manually supplement the printer underwipe process.

[loki42]

Oh that's great, the ultrasonic stencil cleaners I've been looking at are much more pricey (25k usd) and need a lot of current.  What does a stencil from Alpha cost?

[SMTech]

No idea we haven't used Alpha in quite a long time, stopped using them when we stopped using framed stencils, they weren't cheap tho' so the tension frame was a fairly quick payback.

How do you find your MPM? Easy to use/maintain? Quite pricey new...

[loki42]

The mpm is a good bit of kit. Well built and well designed.  We got it used though and it needed a bit of work.  I was stupid and bought it from a dealer and should have saved a lot of money and got it at auction.  They come up often at auction. It is big and very heavy (3500 kg). It's been hard to get working perfectly but I think that's because it's a hard part of the process to get prefect rather than the machine.  We've been trying to tune board support,  wiping options,  paste,  printing parameters.  The built in inspection is good for stencil blockage and pad coverage but doesn't give you an idea of volume so I think 3D SPI is still useful.  I've bought a Koh young spi which is annoying because it takes up room without putting parts down but hopefully it reduces waste.