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SMT Trends and Technologies: Pick and Paste

What defines a good electronic product coming from a production line? All process variables need to be 100% without any influence from outside, which means all machines producing in exactly the same way, in exactly the same environment. In the printer, for example, the paste must be evenly distributed at exactly the right locations and in exact amounts. The pick-and-place equipment must place components precisely, with the right force at the right board coordinates--and all perfectly cured in the oven.

The reality is normally quite different, which explains the need for inspection units in the line to verify various steps in the production line. One of these units is the solder paste inspection (SPI) system. Offsets can be determined by solder paste inspection and results fed back to the printer (paste volume data) or downstream equipment (paste offset data).  

Solder Print Offsets

At the pick-and-place equipment, the actual mount data (coordinates plus correction) is based on a calculation based on reading fiducial marks. The result is a placement according to CAD data. However, even if all seems to be correct, the board yield will not be undesirable if all process variables are not what they are supposed to be. Solder print offsets, for example, will eventually lead to board errors. This is most problematic for components requiring highly accurate placement, or very small components like 08004, 01005, 0201 and Rnets.Read the full column here.Editor's Note: This column originally appeared in the November 2013 issue of SMT Magazine.