Photoresist Developers | Dry Film, Liquid Resist & Solder Mask

Cleaning the metal surface is extremely important when it comes to developing. A clean surface means no dirt will interfere with the exposure step, and lamination adhesion is improved.
Alkaline Clean is the first cleaning step and is used to remove all oils and organics from the surface.
Acid Clean is the second cleaning step and removes any contaminants that remain on the surface. This chemistry will micro-etch the surface, which increases lamination adhesion.
To further increase lamination adhesion, chemical milling companies should make their post-acid clean rinses slightly acidic. A slightly acidic rinse will create an acid surface that reacts with the lamination to improve adhesion.
PCB industry companies can Increase lamination adhesion by micro-etching the surface prior to lamination.

Hot Roll Lamination— pre-heating the board before applying the dry film photoresist—is used to increase resist adhesion and avoid photo resist wrinkling, especially if the metal is thick.
Liquid Resist is recommended to attain high resolution for developing and etching.
Thinner Photoresist typically gives tighter tolerances because the channel the chemistry needs to enter is shorter. A shorter channel allows the chemistry to flow in and out better.
Hold for 30 minutes after lamination to allow the resist to lock into the metal.

As products continue to get smaller this has become one of the most important pre-developing steps.
A speck of dirt is enough to cause an open circuit on fine lines. The slightest misalignment on artwork top to bottom has the potential to shift dimensions outside the tolerances.
This is not a Chemcut process, but over the past seven decades, we have learned a lot about photoresist exposure. Below is a small list of topics we believe are important for the best exposure:
- Clean
- Yellow room is a must have
- Collimated light for fine features
- Features that help create near perfect alignment
- Hold for 30 minutes before developing for better resolution

Developing is often viewed as less critical than etching. While that may be true, it does not mean you can overlook the developing step.
Photoresist can be underdeveloped or overdeveloped. Underdeveloped means all the unpolymerized resist was not completely removed. You did not fully expose the metal that you want to etch away, resulting in smaller holes, no breakthrough for chemical milling, and shorts for circuits.
Overdeveloped means the developing solution started to undercut the resist. As a result, the resist may lift while etching, which means you will lose resolution and worse, etch away metal you want to keep. For chemical machining, you may end up outside your tolerances. For circuits, you may end up with open circuits.