Product Code: ICAL07_1402

Reduction of Thermal Damage in FR-4 with Progressive Percussion Drilling
Authors:
Leonard Migliore, Coherent, Inc.; Santa Clara CA USA
Presented at ICALEO 2007

Glass-epoxy circuit boards (FR-4) may be cut with carbon dioxide lasers. This process is commonly used for separating individual circuits from a larger multi-circuit panel. The cutting process, however, generates substantial amounts of carbonaceous decomposition products, resulting in charring. Charring has the potential to create unwanted conduction paths and makes the edge cosmetically unattractive. Charring may be mitigated by a multipass cutting procedure using pulses spaced apart by several times their diameter. A series of passes with the pulse locations controlled to fill the spaces completes the cut. With the appropriate pulse energy, pulse spacing and number of passes, the resulting cut exhibits greatly reduced levels of char in comparision to single-pass cutting or conventional multi-pass cutting with overlapping pulses. Charring is further reduced by the use of a 9-micron CO2 laser instead of a conventional 10-micron CO2 laser because epoxy has much higher absorptivity in the 9 micron band.