Micro via drilling in multi layer high density printed circuit boards

Applications in the Printed Circuit Board (PCB) industry seemed to be well suited to the Copper Bromide Laser as a result of the high energy and small spot size. A large market exists for drilling micro vias in printed circuit boards.

A Laser system has been developed and successfully used to drill micro vias. The laser system trepans in a circular fashion to remove first the top copper layer. The power is then reduced and the dielectric begins to be drilled, the diameter of the trepan is slightly reduced so that a conical hole is produced.

100 micron hole is drilled in copper and dielectric in one action		The hole is then electroplated to make the interconnect

A diagrammatic representation of a multi layer completed circuit board.

There is sufficient power available in a Norseld Copper Bromide MOPA Laser to drill 4 holes at a time thus a multi head laser driller was developed. Each laser head is capable of drilling holes down to 20 micron in diameter and up to 200 micron in diameter.

A recent innovation in the Norseld laser drilling head is to depart from the traditional scanning head to using a system which permits on-line imaging of the hole as it is being drilled. This permits the on-line quality monitoring of the drilled via.

Another important feature of the system is that the Copper Bromide laser is capable of drilling both the copper and the dielectric whereas all other systems require the hole to be drilled in two stages. First the copper is either cut with a laser or etched using traditional photolithographic methods then a second laser is used to remove the dielectric. This leads to a much slower process and increased inaccuracies in the process.