Layer to Layer Registration Tolerances
The accuracy of the layer to layer registration is an important parts of PCB manufacturing process and it relates too:
- Pattern to Pattern Registration of an Inner Layer Core (e.g. L2 to L3).
- Inner Layer Core to Inner Layer Core.
- Outer Layer Pattern to Inner Layer Core(s).
- Outer Layer Pattern to Outer Layer Drill Pattern.
Understanding, managing and compensating for processes that influence the layer to layer registration accuracy we are able to reduce them to a minimum.
We use a combination of mechanical pins and fiducials together with the optical registration systems to ensure that the registration is within the allowable tolerance.
With the introduction of Direct Imaging (DI) especially for the Soldermask we have improved our registration capabilities and been able to reduce the minimum Soldermask annular ring.
It is important to understand what influences the layer to layer registration accuracy so that we can compensate for them during production.
When using traditional exposure units with film the main influences on registration are:
- Film distortion due to temperature and humidity.
- Film punched registration holes and the accuracy of the hole punch.
- Exposure systems camber registration accuracy.
When using Direct Imaging the main influences are:
- UV Marker positional tolerances for inner layers.
- Hole position tolerances.
- DI system registration accuracy.
Understanding and knowing all of these tolerances allow us to manage the layer to layer registration accuracy to avoid annular ring breakouts.