Process topics


 Differences between liquid resist and dry film: Superiority of the dry film
Generally, liquid resist is positive type and its exposed area is dissolved during development. The exposed area of dry film, which is of negative type, is hardened. It is necessary for a user to control the stability of the film thickness of the liquid resist during coating. Controlling the film thickness with high accuracy is difficult due to its liquid state although it depends on the coating method. Variations in film thickness in coating process may cause variations in etching accuracy. However, the thickness of the dry film does not change and there is no necessary for a user to control the resist thickness.
Therefore, high etching accuracy can be obtained. In addition, dry film can reduce environmental load compared with liquid resist due to waste liquid disposal, etc.
 Is there a positive type dry film?
Since the resin component of a positive type resist is hardened in the temperature range of 5°C-20°C, film processing is difficult. However, if requested, we will examine whether we can propose a negative type resist. Therefore, please contact us.
 What kind of substrate can be applied with dry film?
It can be applied to stainless steel, 42 alloy, invar alloy, etc., in addition to copper, which is generally used for Circuit formation. In the case of copper, it can be applied to electroless copper, electrolytic copper, rolled copper foil, sputtered copper, etc.
 Relationship between developing solution concentration/temperature and adhesion
The following table presents the relationship between the developing solution temperature/concentration and the adhesion of an isolated line of resist in case of our standard resist for plating. Generally, there is a tendency that a decrease in concentration and temperature of developing solution reduces the load to resist and improves adhesion. However, if the B.P (breakpoint) is too slow the load to resist increases and adhesion deteriorates.

The resolution indicates no significant differences at the temperatures of 27°C-30°C and concentrations of 0.7%-1.0%.

 What are the advantages of the subtractive and semi-additive processes?
Semi-additive process has an advantage in the formation of fine circuits although there is a tendency toward high costs because the semi-additive process has more process in comparison with the subtractive process. On the other hand, the subtractive process is superior in through put and process cost, but it is more disadvantageous than the semi-additive process in the formation of fine circuit because side etching is generated during etching process. However, in recent years, the refinement of circuit patterns has progressed in the subtractive process due to the introduction of ultrathin copper foil, development of dry film with high resolution adhesion, and evolution of etching technology.

Subtractive process
Intrusion of etching solution not only vertically but also laterally; generates side etching.
Semi-additive process
Vertical accumulation of plating prevent from the problem of side etching. This is used for fine circuits. The important features are the shape and plating resistance of the dry film.
 Relationship between stripping condition and stripping piece
The general relationship between the size of a stripping piece and the concentration and temperature of the stripping solution (NaOH) is depicted in the following diagram. In the condition of low concentration and high temperature of the stripping solution, the stripping piece presents the smallest shape (dispersion). Conversely, there is a tendency that the film is stripping in the condition of high concentration and low temperature of the stripping solution. In addition, dispersion differs depending on individual products.

 Note for handling concerning temperature, humidity, illumination, etc.
Please store the products in a cool and dark place at 5°C-20°C and 60%RH or less. Leave a product stored in a refrigerator in a clean room for a while prior to use to avoid dry film to condensation. Since dry film is photosensitive to natural light, please handle it under a yellow lamp. When storing substrates with laminated dry film before exposure, it is recommended to shield it from light using a black PE sheet.