The real physical size of the hybrid is determined after it comes out of the furnace. Making a proper stencil can take from one day to two weeks depending on the complexity of the pattern. With automated dispensing systems, physical changes in the size of the substrate are not a problem because new coordinates can be taught to the machine in minutes, not days or weeks.
Aided by a vision alignment system, it is just a matter of teaching the machine two coordinates, which can be any contrasting features on the substrate. The automated system takes it from there and dispenses the correct pattern.
Vision Alignment Systems
A good vision alignment system can counteract the problem of fired substrate shrinkage and also the alignment problems faced when fixturing tiny chips. After being taught the fiducials, which typically only takes a few minutes, the vision system instructs the dispensing system to shift it's data file to dispense where it actually "sees" the part, rather than where the part is supposed to be. This automatic inspection process will guarantee accurate dispensing on every part regardless of the size, placement, or whether the part is bare or hybrid.
Also in the process of firing ceramic substrates, there are mechanical instabilities in the material. When fired, the ceramic material can come out with a twist or camber to it (bows).
Because of this, the surface is no longer flat. If a large substrate has these abnormalities in it and is "pulled" flat or level by a vacuum plate, it can break. Often, when dealing with multiple chips within a waffle pack or other transport/holding device, every chip is not level. The holding device itself may have slight warp or abnormalities that cannot be seen with the eye. This is where a non-contact height sensor can be extremely helpful.
The pump dispenses from above the receiving surface. For complete accuracy, the height of the dispensing tip above the hybrid is critical to the volume of the dot. If the receiving surface is uneven, the height between the dispensing tip and the substrate (stand-off distance) is subtly changed. Given the minute size of the dots and close tolerance of patterns, height is extremely important.