32

Poor Hole
Fill This example shows poor wetting of the surface of the pads and is likely to be due to the thickness of the tin/lead coating. Solder levelling often leaves a thin deposit on the surface of the pads and on the edge of the hole. This defect is often referred to as the weak knee effect where the solder fails to wet over the knee of the hole and on to the pads. Poor hole fill can also be due to the pre heat operation being set too low or poor flux application. In both cases a check on the process parameters should eliminate the problem. Reference to the set-up and process control procedures included on this CD should assist in eliminating problems in the future.