Introduction
There is considerable interest in using ink jet technology to directly apply
either photoresist to a substrate or even the actual metal conductor material
thus bypassing the masking and exposure steps normally used when producing
PCBs.
A problem that arises is that the diameter of the “ink” droplet is often fairly large relative to the width of the lines and gaps that
one wants to image on the substrate. One cannot merely use a higher DPI to
achieve line precision and edge smoothness since there will be too much ink
applied.
Droplets must be tightly spaced in order to produce a smooth edge. However this
can result in so much ink that it will flow outside of the desired boundary.
To achieve optimum ink density it is necessary to "remove" a large percent of
the droplets . But if one simply attempts to uniformly remove the ink droplets
the result is jagged edges and poor linewidth tolerances. One needs to
precisely control spacing of droplets along the edges to form a smooth edge and
possibly wider spacing along the interior to control the total ink delivered.
Optimally spaced droplets are a tradeoff between overlap and edge smoothness.
The Edge Rasterizer differs from a standard rasterizer in that it assumes that
the pixel grid is much finer than the narrowest region to fill. For example, if
you need to fill lines of 50 um in width you will need a grid that is 8 to 10
times finer than this value in order to precisely place the droplets. The Edge
Rasterizer also knows that the spacing between pixels must be carefully
controlled in order to avoid ink run out. The actual droplet diameter can be
close to the minimum width of the line as long as the droplet placement can be
precisely controlled.
In the snapshot above, the cyan grid represents a 5080 DPI grid (i.e. a droplet
can be placed on 5 um centers). The blue line represents the conductor boundary
- in this case a narrow trace about 60 um wide connecting into a round pad of
approximately 450 um in diameter. The inkjet droplet is 40 um in diameter and
the nominal pitch between droplets has been set by the user to 20 um.