Enhancing Photoresist adhesion
Back to InnerlayersPerma-Etch® DFPerma-Etch® DF*
*United States Patent #4,437,931 #4,437,932Product Description
The PERMA-ETCH® D.F. Process is a sprayable microetch for copper on printed circuit boards, and is based on hydrogen peroxide and sulfuric acid. It is designed to provide the optimum topography prior to application of organic coatings such as liquid or dry-film photoresist and solder masks. The PERMA-ETCH® D.F. Process is specifically designed for spray application where 50 to 100 microinches (1.25 - 2.5 microns) of copper are to be removed in 10 to 60 seconds.The etch rate of a PERMA-ETCH® D.F. solution is controlled by proper selection of PERMA-ETCH® Replenisher concentration and temperature as shown in Figures 1 and 2. The etch rate is consistent regardless of copper concentration within the normal operating limits.
The copper removed from the board by etching can be recovered from the PERMA-ETCH® D.F. solution in the form of copper sulfate pentahydrate by using a continuous recovery system. This feature allows the PERMA-ETCH® D.F. solution to be replenished and used indefinitely without dumping. Consult Electrochemicals' Technical Service Department for specific recommendations on recovery systems. Alternatively, the PERMA-ETCH® D.F. solution can be dumped when the copper concentration reached 52.5 - 60 g/L (7 to 8 ounces per gallon).
Applications of the PERMA-ETCH® D.F. process include:
Microetching of innerlayers prior to conveyorized spray oxide coatingThe use of the PERMA-ETCH® D.F. Process eliminates the need for a pumice scrub prior to photoresist application or screen printing.
Microetching of innerlayers before application of photoresist
Microetching before solder mask application (SMOBC process)
Solution makup
| PERMA-ETCH® D.F. Make-Up | 80% by volume |
| Sulfuric Acid (used only with recovery systems) | 10% by volume |
| PERMA-ETCH® Replenisher | 2 - 10% by volume |
| Deionized Water* | Balance |
Mixing instructions
1. Add the required amount of PERMA-ETCH® D.F. Make-Up.2. If necessary, slowly with mixing add the required amount of sulfuric acid. Do not allow the temperature to exceed 49°C (120°F). (CAUTION: Considerable heat will be evolved.)
3. Add the required amount of PERMA-ETCH® Replenisher.
4. Fill to volume with deionized water*.
* Make sure the deionized water is chloride free as chloride contamination will result in a rapide decrease in etch rate.
Operating conditions
| Nominal | Range | |
| PERMA-ETCH® Replenisher (% v/v) | 3 | 2 - 10 |
| Sulfuric Acid (% v/v) | 10 | 8 - 20 |
| Copper | 20 g/L (2.7 oz./gal.) |
4 - 60 g/L (0.5 - 8 oz./gal.) |
| Temperature | 43°C (110°F) |
32 - 49°C (90 - 120°F) |
| Dwell Time (sec.) | 20 | 10 - 60 |
| Total Etch Amount | 1.25 m (50 min) |
0.25 - 2.5 m (10-100 min) |
