Print Process Parameters

Transcription

1 Print Process Parameters INTRODUCTION The purpose of this Application Bulletin is to highlight some of the critical Print Parameters that are often found to cause problems in the field. Settings addressed in this Bulletin are:. Print Speed. Release Speed. Release Delay. Downstop. Lift/Dwell Height. Paste Replenishment. Squeegee Height & Length. Print Pressure 1. PRINT SPEED Always observe recommended squeegee speed for specific solder paste products. Note that different speeds may be preferred to maximize print performance for different solder pastes. Certain latest generation solder pastes like OM-338 Series are designed to print fast based on their high shear/fast response characteristics. The table below provides conversion between metric and imperial values. Inch/sec 1" 2" 3" 4" 5" 6" 7" 8" 9" 10" mm/sec 2. RELEASE SPEED Observe recommended release speed for specific solder paste products. Note that certain latest generation products require fast release speeds (or no release speed), based on the thixotropic nature of these products (like OM-6000 and OM-338 Series). Use a microscope to judge the different print results with different release speeds. 3. RELEASE DELAY For solder paste stencil printing, never use a release delay to avoid solder paste from adhering to the aperture walls in the stencil. 4. DOWNSTOP For good printing, the squeegee downstop should be set at 1.9 to 2.2 mm ( mil) to avoid excessive squeegee bending, resulting in solder paste sticking to the squeegee holder. The squeegee angle should be approximately 45.

2 5. LIFT or DWELL HEIGHT Lift Height (MPM) or Dwell Height (DEK), should be set within the range of 8 14 mm (1/4 3/5 ). This range prevents solder paste from sticking to the blade when the paste roll is too small, while avoiding dropping from the blade if the roll (weight) is too much. In both cases, the result might be missing deposits. The majority of the solder paste roll should always remain on the stencil. Note that some MPM printers have a tilt squeegee head; in this case, the 8 mm (1/4 ) Lift Height should not be exceeded. D Printing Status: R Stopping SQ Status: Solder Paste remains on the stencil mm 6. PASTE REPLENISHMENT When the above settings are used an additional benefit is that this provides a good indicator for the operators when to add new solder paste:

3 1. When the curtain is perfect: no need to add solder paste 2. When some holes are noticed in the curtain: add ± 50% of the solder paste pot (or ± 250 grams) 1. Solid Curtain: no need to add solder paste 2. Holes: add about 250 gram solder paste The tables below provide weight indications in grams for given squeegee lengths versus paste roll diameter. This information is useful for operators to estimate the amount of solder paste to be added while avoiding a paste roll to ELJWKDWPLJKWHQGXSVWLFNLQJWRWKHVTXHHJHHKROGHU7KHIRUPXODXVHGLVDVIROORZV 5 2 x SQ x 4, whereby R = ½ roll diameter in cm and SQ is Squeegee Length in cm and 4 is approximate density of paste. R D SQ

4 Diameter Paste Roll (Inch, ") Weight in Grams Diameter Paste Roll (cm) Weight in Grams ,029 1,081 1,132 Squeegee Length (Centimeter, cm) ,030 1, SQUEEGEE HEIGHT & LENGHT To select the proper blade length, add mm (1 2 ) to the width of the print image. For example a 200 mm (8 ) print image requires a squeegee length of mm (9 10 ). To avoid solder paste sticking to the squeegee holder, the optimum squeegee height is 38 mm (1 1/2 ). This equals also the maximum software limitation for DEK & MPM printers. 8. PRINT PRESSURE Print Pressure is typically expressed in Kilograms per Centimeter (kg/cm) or Pound per Inch (Lb/ ) and require conversion relative to the blade length. Pounds per Inch (Lb/") Kilogram per Centimeter (kg/cm) The tables below provide print pressure settings based on squeegee length (metric & imperial). The workable range is from 0.16 to 0.35 kg s per cm (0.9 to 2.0 pounds per inch) to avoid damage to stencils & squeegee blades.

5 Squeegee Pressure (Pounds per Inch) Pressure in Pounds (per Inch) Squeegee Pressure (Kilogram per cm) Squeegee Length (Centimeter, cm) Pressure in Kilo (per Centimeter) Squeegee Pressure (Kilogram per cm) Pressure in Kilo (per Inch)