Understanding_ the_Cleaning_Process_for_Automatic_Stencil_Printers - 第16页

Event d riven wiping • Key events that can t rigger defects: • Pause in printing • Fir st 1 - 4 prints • Additional paste added • Cust om Wipes t o t a r get specif ic events in the print er • Pause in printing • Based o…

Additional Parameters

• Recent studies have shown a Vac/Vac/Dry or a Solvent/Vac/Vac/Dry wipe is most effective

• The first vacuum wipe pulls solder from the aperture and forms stalactite's hanging from the aperture

Continuous vs index mode

• Continuous mode – advances the paper during wiper motion ensuring fresh paper is applied during the wipe – maximum paper

consumption

• Index mode – paper is advanced a pre-determined amount then is stationary during wiper motion – minimum paper consumption

• Continuous has shown to clean better and prevent “snowplowing” of the paste particularly when vacuuming

Hop over

• Used to address snowplow effect – retracts plenum and moves over end point

Overtravel

• Wipe stroke pre-determined by squeegee stroke – allows extension of stroke – eliminates contamination of gold fingers if present

Wiper speed

• Recommended speed of wipe or solvent stroke – 2 Inch/second

• Recommended speed of Vacuum stroke – 1 inch/second

Understanding the Cleaning Process for Automatic Stencil Printers

Event driven wiping

• Key events that can trigger defects:

• Pause in printing

• First 1-4 prints

• Additional paste added

• Custom Wipes to target specific events in the printer

• Pause in printing

• Based on thixotropic index of paste

• Recommend a medium plus wipe

• Kneed function

• Squeeze out is the issue

• Heavy on the dry wipe / no solvent

• During paste dispense

• Utilize printer window to do additional wipe

Understanding the Cleaning Process for Automatic Stencil Printers

Wiper Paper

• “Printers are only as good as the material that you put into it” – the same can be applied to the wiper

• Using low-cost paper directly influences the wiper ability to clean the stencil

• In general, there are two types of papers used in stencil wiping: papers made with synthetic fibers held

together with glues (called binders), and papers made from a mix of natural and synthetic fibers that do not

use glue.

• The papers ability to absorb both the solder and solvents reflects on the cleanliness of the stencil

Understanding the Cleaning Process for Automatic Stencil Printers