Prevention of Ultra Violet Exposure through Thin Laminate
Original Publication Date: 1996-Jul-01
Included in the Prior Art Database: 2005-Mar-31
As package density becomes greater, individual layers have decreased in thickness to accommodate more wiring per unit volume. The fully additive electroless process does not use copper foil for circuitization. Without this opaque copper layer, Ultra Violet (UV) light can more readily pass through thin laminates such as epoxy-glass less than about 7 mils thick. This phenomena is referred to as "bleed-through". Bleed-through on thin laminates can cause photoresist on the opposite side to partially polymerize. The result is incomplete development and subsequent copper voids when using the fully additive circuitization process. The affected side is always the first side exposed. However, if both sides are exposed simultaneously, the defect does not occur.