Simulating Surface Height and Roughness
of Ink Jetted Conductors
Contributions to Surface Roughness
There are many process variables that contribute to conductor surface roughness.
Our simulator can only address one issue -- how droplet placement and overlap
produce height variations. Unlike some inkjet applications, the conductor
droplet diameter is very close in size to the line width -- therefore the
positioning and overlap of the droplets contributes significantly to surface
roughness.
Consider the case of a copper trace produced bya pass of the inkjet heads with
overlapping droplets as shown at right. There are five levels of ink converage
beginning at 0 (where no ink at all is deposited) up to a maximum of 4 where 4 “levels” of ink are deposited.
Clearly the surface of this trace will have significant height variations even
when accounting for a certain amount of levelling due to ink flow.
One of our objectives is to optimize the pattern of drops used to fill narrow
traces so as to produce a smooth edge and a smooth surface. To evaluate
different software algorithms to determine the best approach, we need a “tool” that provides some feedback as to the actual surface height.
Otherwise we have to rely on many time consuming and expensive physical tests
and evaluations to provide feedback.
Even a single pass will have height variations due to overlapping droplets.
Multiply this by the number of passes and maintaining surface flatness becomes
a problem.
Our droplet simulator is designed to provide some useful feedback on the effect
of droplet overlap and patterning on the thickness and roughness of the
surface. It has been designed with “plug-in” algorithmic modules so that it can be easily modified to support different ink
flow phyiscal models.