| | | Hi, | | | I'd like to ask some tips about the merits and shortcomings o | | | of both screen printer and stencil printer. For small quantity and highly mixed usage, which type of printer is suitable to our | | | application? | | | The boards contain no BGA and the finest lead pitch is 15mil PLCC. | | | Thanks for any advice. | | | Carol | | | | | | Hi Carol | | If you are talking 15 mil you are looking for a stencil printer, laser cut or electroformed stencil and a metal squeegee. Save the stencil printer for the company tee shirt. Actually the printer would be the same with either a full mesh screen with resist defining the apertures or a foil stencil with fully open apertures mounted to it. You just won't get the accuracy and definition needed when pushing the paste through a mesh screen. good luck | | John Thorup | | | | | In addition to John's comments I recommend the laser cut stencil apertures for 15 mil pitch to be trapezoidal and electro-polished for better paste release. | Mik Horvath |
Carol,
I used to make screen printers for thick film hybrids. They can print two mil lines and spaces. Makes your 15 mil pitch look like a cake walk. I now make screens and stencils. My recommendation: shop by requirement, there is no general rule.
If you need automation, vision, system intergration, throughput, look to the big SMT printer manufacturers. You'll need lots of money. If want some automation without the big dollar price tag, try some of the screen printer manufacturers with equipment adapted for SMT. If you want table top manual machines they are several out there, but you will struggle with the 15 mil pitch.
Screens are good for prototypes, but they wearout quick, they are also less expensive. They don't print solder well, but there are screen printable pastes available.
A stencil is the way to go, if possible, trapizoidal aperatures and electropolishing will help paste release on fine pitch, but save the expense on boards with nothing under 25 mil pitch. Laser is probably best from most vendors under 16 mil pitch in foils 5 mils thick or thicker. We chem etch everything and have had great results to 16 mil in 5 mil foils. Pricing will depend on your vendor. Laser is usaully more expensive. Some vendors sell "hybrid" stencils with chem etch and laser cutting on the same foil to keep price down. Metal squeegee is best on either.
Let your process and budget determine your needs, not the terminology of an industry that has trouble keeping up with itself. Good Luck...Dan.
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Hi,
I'd like to ask some tips about the merits and shor...
- Aug 18, 1999
by
Carol Zhang
