Subtractive methods remove copper from an entirely copper-coated board to leave only the desired copper pattern. In additive methods the pattern is electroplated onto a bare substrate using a complex process. The advantage of the additive method is that less material is needed and less waste is produced. In the full additive process the bare laminate is covered with a photosensitive film which is imaged (exposed to light through a mask and then developed which removes the unexposed film). The exposed areas are sensitized in a chemical bath, usually containing palladium and similar to that used for through hole plating which makes the exposed area capable of bonding metal ions. The laminate is then plated with copper in the sensitized areas. When the mask is stripped, the PCB is finished. COUNT 5
QSN1 Do additive or subtractive methods use less raw materials? ANS1 additive QSN2 What object is used to expose selected parts of the photosensitive film to light? ANS2 mask QSN3 What chemical element is often present in the bath used to sensitive exposed film after it's been imaged? ANS3 palladium QSN4 In subtractive methods, what metal covers the board and is then partially removed? ANS4 copper QSN5 In the additive method, which parts of the laminate are plated with copper? ANS5 sensitized areas