Positive Printed Circuit Board Photoresist (PCBPR) Product Introduction




Prosperity Integration, Inc. is currently distributing liquid photoresist and the equipment for printed circuit board (PCB) products in the North America. PCBPR (Printed circuit board photoresist) is produced by Everlight Chemical Industrial Corporation (ECIC) in Taiwan. ECIC is a high-tech chemical manufacturer whose development in the research and production technology has achieved distinguished recognition in the field of dyes, specialty chemicals, pharmaceuticals, and electronic specialty chemicals. ECIC is an ISO 9001 & 9002 company and has also awarded ISO 14001 certification. ECIC is a public company and plans on achieving the sales goal of 10 billion NT Dollars in year 2000.  With electronic devices getting smaller and faster, the PCB industry requires new electronic chemical to stay competitive and enter new technical field.
 
Traditionally photoresist applied in PCB patterning is mostly negative dry film photoresist or negative liquid photoresist that has problem in controlling the linewidth during the patterning process because it has swelling phenomena in development. Therefore ECIC has developed positive liquid photoresist to deal with the problem. Positive liquid photoresist which can be applied to process etching of inner- or outer-layer board and can be applied with the appropriate coating methods to achieve better control in line widths, excellent resolution, and good durability at lower cost. In addition, the application of PCBPR on the defective surface copper-clad will not affect its adherence. This will increase process stability.
 
ECIC has developed the positive liquid photoresist with novolak that is different from the major resin of negative photoresit. Novolak is better in many aspects such as linewidth, resolution, hardness, etch resistance, and durability. Under optimal condition, it requires less coating thickness to achieve the performance that results in cost reduction and higher quality. Therefore novolak resin as photoresist is particularly very beneficial to the manufacture of fine line PCBs. Novolak liquid photoresist is currently used in IC manufacturing widely.
 
Prosperity Integration, Inc. looks forward to assisting the customers in the North America to meet their PCBPR and equipment needs in fine line etched PCB prototype preparation and mass production.

PCBPR SPECIFICATION:

Photoresist Type
Positive liquid photoresist
Main component
Resin and photoactive compound
Appearance
Green liquid (under yellow light)
Solid content
30-40%
Linewidth
Minimum 15 um (0.6 mil)
Viscosity (cps)
65-75 (25°C)
Coating thickness
4-5 um (dry)
Dry time
5 min (80° C)
Hardness
4H
Exposure energy
150 mJ/cm2
Developer
PH = 12-13 (Na2SiO3/KOH)
Development time
30 sec

FEATURES:

  • High resolution
  • Reliable tenting up to 0.6 mil
  • Short developing time
  • Superior resistance to all acid plating
  • Easy stripping and filterable
  • Large process window
  • Excellent contrast after exposure for easy inspection
  • Good leveling for copper clad laminate

PCBPR PROCESSING:

Process Condition
Pretreatment Brushing film, degreasing, cleaning
Coating The thickness of wet film, 10-12 um
The thickness of dry film, 4-5 um
Dryness 80oC for 5 minutes
Exposure 150-200 mJ/cm2
Development 1-3 wt% Na2SiO3/KOH
Etching FeCl2/CuCl2
Stripping 2-4 wt%NaOh (aq)

PCB PRETREATMENT FOR PCBPR COATING:

For superior photoresist film adhesion, surface of copper clad laminate is required to clean, dry, free oil, free contaminates.

The procedure to clean PCB is as follows:

1.  The copper-clad laminate surface is cleaned by automatic srubbing machine with acid pumice slurry or cleaning chemicals.

2.  Water rinse.
3.  Cleaned with mixture of aqua solution and 5% H2SO4 rinse. The aqua solution contains 5% H2O2.
4.  Water rinse.
5.  Dryness with clean air.
6.  Dried in oven at 40-65°C for 5 mins.
Note:  If dryness is too long, it will cause oxidation on surface of copper clad laminate.

PCBPR COATING:

PCBPR is coated on copper surface by roll coater or the other coating techniques. Film thickness can be adjusted based on the type of roll coaters used, photoresist viscosity, and solid content. The other coating parameters are listed in Table 1.


TABLE 1


Roll temperature
25 - 40°C (77 - 104°F)
Roll speed
2 – 6 m/min (6 – 19 feet/min)
Operating temperature
25 – 30°C

PCBPR DRYING:

Normally after coating, it prefers to use convection type of clean oven. Two ways to dry PCBPR film can be applied. They can be dried either at static or at continuous-gradient and are listed in Table 2.

TABLE 2

Static
80°C for 5 mins
Continuous-gradient
80 –120°C for 2-3 mins

EXPOSURE:

After drying the PCBPR film in a clean oven, the photoresist coated layer may be immediately exposed and developed for better performance. With contact or proximity broad beam phototool, the mask is positioned above the photoresist film. The exposure parameters are shown in Table 3.
TABLE 3
UV wavelength
350 nm
Vacuum time
3-5 sec
Exposure energy
100 – 200 mJ/cm2

PCBPR DEVELOPMENT:

After exposure, the exposed area is removed in the development step. The developing conditions are listed in Table 4.

TABLE 4

Developing system
1– 3 wt % Na2SiO3/KOH
Developing time
20 – 30 sec
Pressure
Normal pressure

ETCHING:

Etching is conducted in acid solution. The unprotected copper surface will be etched since there are no photoresist to protect. The parameters for etching are shown in Table 5.

TABLE 5

Etching system
H2O2/HCl CuCl2 or FeCl2
Temperature
50°C
Spray pressure
1 – 3 kg/cm2 (15 – 45 psi)
Etching time
100 – 200 sec

STRIPPING:

Stripping is done in alkaline solution. The conditions for stripping are indicated in Table 6.

TABLE 6

Stripping system
NaOH (aq) (2 –4 wt %)
Temperature
40 - 60° C (104 – 140°F)
Spray pressure
1 – 3 kg/cm2 (15 – 45 psi)
Stripping time
50 – 100 sec

PCBPR STORAGE:

During storage of PCBPR, keep off the actinic light and store in a cool and dry place. The storage temperature is recommended at 5 – 20°C (40 – 70°F). The relative humidity is suggested at 60 ± 10%. With the storage at the above conditions, the maximum shelf life and product performance can be assured.

NOTICE:

The information contained herein is correct to our knowledge. As different type of equipment result in different outcome slightly. The suggested process parameters are based on the experience from the laboratory and the production lines.