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A focussed laser beam with very short pulses (10-50 ns) has been used to create vias in polyimide overlying a metallurgy layer by controlled surface evaporation of underlying metal.
English (United States)
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Generation of Vias in Polymide by Rapid Heating and Controlled
Evaporation of Underlying Metallurgy with a Pulsed Laser
A focussed laser beam with very short pulses (10-50 ns) has been used to
create vias in polyimide overlying a metallurgy layer by controlled surface
evaporation of underlying metal.
The underlying metallization may be part of a signal line, a capping layer over
another via in a multilayer ceramic structure or a mesh plane for power
distribution. Vias may be formed in an overlying polyimide layer in a single step,
automated, maskless process with only one (possibly automated) registration
The figure illustrates the method in which vias are generated: (1) Use a laser wavelength at which the polyimide is highly
transparent, so that very little of the incident light energy
is absorbed in the polyimide. (2) Use a very short laser pulse with appropriate energy per
pulse so that the power density in the laser focal spot is of
the order of 10/8/ to 10/9/ watts/cm/2/. Under such
even though the energy is very low (of the order of tens of
microjoules), the extremely high rate of supplying the energy
over a very small area causes the exposed metallurgy to be
heated rapidly and evaporate. The depth of the exposed
evaporated is determined by the pulse energy and can be
precisely. This controlled micro-evaporation of the
surface metallurgy causes the polyimide above the laser