This page sponsored by

The solder paste example in Figure 1 shows a paste deposit smudged on the edge of the circuit board on a chip component location. The paste volume has been affected as well as residue of the paste on the surface of the resist which will probably lead to solder balling.

The example is most likely due to poor handling of the board after printing. The pads are very close to the edge of the board, less than the recommended 4mm edge clearance for handling and racking of printed boards.

Figure 1: Smudged paste deposit on the edge of a circuit board.

 

The solder paste deposit in Figure 2 has been smudged or flattened. If this was the condition as it exited the printer it has most likely come into contact with the base of the stencil. This contact has caused the paste displacement.

This could have been caused by too higher force on the stencil causing it to wipe back to the surface of the board after separation. The stencil may not be level or parallel to the board surface causing a different height after separation.

Figure 2: This solder paste has been smudged or flattened.

 

In Figure 3, he original paste deposit would appear to have been satisfactory but after printing the deposit has been smudged. This is more than likely to be due to contact with the stencil, the stencil has either flexed during separation with the board or the board has lifted. The stencil has literally patted down the surface of the paste.

If it was hand contact the damage to the print would be more obvious, or it could of course be the ESD lead or the engineers tie or the operators sleeve smudging the print!

Figure 3: A smudge that occurred during board/stencil separation.

 

Damaged Stencils	Stencil Blockage	Paste Misalignment	Smudged Paste	Poor Definition
Incomplete Prints	Residues	Bleeds	Ears	Scooping
Shorts	Slump	PIHR Printing