Printing Defects

Printing Defects (6)

Please see below answers concerning your printing defects.

What is Under Stencil Cleaning?

Under stencil cleaning rollers ensure that the screen of solder paste printing machines are kept clean and work efficiently, in other words, it is the cleaning roller for the bottom of the printing screen.

They are non-woven materials with a high durability rate, which do not leave dust and similar residues behind, are also suitable for vacuum cleaning and have a very high suction permeability, which are used for cleaning solder paste residues and other dirt-causing substances after solder paste printing. It can also be used wet or dry according to preference.

The machines suitable for the use of under-screen rolls are mainly ASM DEK and many other global brand machines and are available in different sizes according to demand. 400mm, 510mm and 600mm are the most preferred 3 types of under-screen rolls and you can view the length details of these rolls from the table below.

Model 1: 530mm x 510mm (53cm long)
Model 2: 530mm x 400mm (53cm long)
Model 3: 622mm x 600mm (60cm long)

Roll Type Main Width (A) Fabric Width (B) Roll Diameter (C) Inner Diameter (D) Roll Length (F)
400mm roll 530 mm 400 mm 56 mm 19 mm 10
510mm roll 530 mm 510 mm 56 mm 19 mm 10
600mm roll 622 mm 600 mm 56 mm 19 mm 10

You can examine the technical specifications of our high quality under stencil rolls that Assemcorp offers for sale below.

Main Components: 45% polyester, 55% cellulose
Weight: 68 g/m2
Thickness: 0.29 mm[...]


What are the reasons of bridging?

Are apertures larger than pads?
Is there any space between stencil and the PCB?
Is stencil thicker than 0.150 mm?
Is stencil damaged?
Is the green dye thicker or thinner than the pads?
Are ther any solder masks, stickers and etc. near bridging?
Are tin coated pads smooth?
Is the viscosity of the solder paste too low? (metal ratio less than 89%)
Is printing area wet and hot?
Is squeegee wear down?
Is squeegee soft? (less than 90 shores)
Is squeegee pressure too high? (more than 2kg per 100 mm0)
Is printing misaligned?[...]


What are the reasons of excess printing height?

  1. Are there solder paste over the stencil surface?
  2. Is squeegee torn down?
  3. Is there a void between stencil and the PCB?
  4. Is squeegee edge damaged?
  5. Is squeege pressure too low? (for 100 mm squuegee width, less than 1 kg)
  6. Are PCB supports weak?
  7. Is stencil damaged?
  8. Are there any solder paste, mark ink or similar material left around the area?


What are reasons of misprinting?

Are there enough solder paste infront of the squeegee (app. 15 mm radius roll).
Does previous solder paste stick to squeegee?
Does the solder paste infront of squeegee drag instead of rolling?
Does the solder paste stay on the stencil surface?
Are apertures less than half of the pitch size?
Is the stencil thicker than 0.150 mm?
Are apertures clogging?
Is stencil deformed?
Is the green dye thicker or thinner than the pads?
Are ther any solder masks, stickers and etc. near misprinted?
Are tin coated pads smooth?
Is the viscosity of the solder paste too much?
Is solder paste old and dry?
Is the solder paste left on the stencil more than tens of minutes ?
Is it cold in printing area?
Is it uniform at squeegee edges?
Is squeegee blunt?
Are squeegee edges damaged?
Is squueegee speed too much for solder paste?
Is squueegee pressure too low? (for example less than 1kg/100mm squeegee length )
Are PCB supports weak?
Is squeegee too soft (less than 75 shores)
Is squeegee pressure to high? (for example more than 2kg/100mm through squeegee length).
Is seperation speed less than 0.5 mm/s or more than 10 mm/s?[...]


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