PCB News - PCB production-pattern transfer process

The graphics transfer process is one of the key processes in the printed board manufacturing industry, and every link must be taken seriously. If this process is well controlled, the subsequent processes will be much easier to do. Based on the author's many years of experience in the process control and management of graphics transfer, this article has gained some insights, in order to avoid unnecessary quality problems in graphics transfer, for reference and correction by colleagues at all levels.

1. Grinding board

1. Surface treatment to remove oxides and other contaminants on the copper surface.

a----H2SO4 2-2.5% (V/V) is prepared for sulfuric acid tank with the largest panel surface (generally vertical 18"*24") made by submerging, it is advisable to replace it once per 100 square meters, and wash it with running water every day Rinse tank.

b----Acid pickling (2-2.5% H2SO4) time 5-10S (5 pieces can be put into a fan each time), washing time 5-8S.

2. Test the width of the wear scar. The grinder used by the author is a 500-mesh needle brush, with a control range of 8-15mm. If the wear scar exceeds 15mm, there will be oval holes or no copper at the edge of the hole. Generally, it is appropriate to control 10-12mm.

3. Water abrasion test: daily test water abrasion rupture time ≥ 15S, the test shows: under the same conditions, the width of the wear scar is proportional to the water abrasion rupture time

4. Grinding plate control The conveying speed is 1.2-1.5M/min, the interval is 3-5cm, the water pressure is 10-15Psi, and the drying temperature is 50-70 degree Celsius.

2. Dry film room

1. The cleanliness of the dry film room is above 10,000.

2. The temperature is controlled at 20-24°C, and it is easy to cause deformation of the film if the temperature exceeds this range.

3. The humidity is controlled at 60-70%, and it is easy to cause deformation of the film if the temperature exceeds this range.

4. Workers must wear dust-proof clothing and dust-proof boots for 15-20S each time they enter the dry film room.

Three, film

1. Film parameter control (The dry film used by the author is generally DuPont PM-115 series)

a Temperature 100-120 degree Celsius, fine line control 115-120 degree Celsius, general line control 105-110 degree Celsius, thick line control 100-105 degree Celsius.

b Speed 1.5-1.8M/min, interval (manual film sticking machine) 8-10mm.

c The pressure is 30-60Psi, generally around 40Psi.

2. Matters needing attention

a When attaching the film, pay attention to the temperature of the board surface should be kept at 38-40 degree Celsius, the cold board film will affect the adhesion of the dry film and the board surface.

b Before applying the film, check whether there is any debris on the board surface and whether the board edge is smooth, etc. If the board edge burrs are too large, it will scratch the film rubber roller and affect the service life of the rubber roller.

c Under the condition of constant air pressure, the transmission speed can be appropriately increased when the temperature is high, and the transmission speed can be appropriately slowed when the temperature is low, otherwise there will be wrinkles or weak film, and it is easy to produce infiltration during pattern electroplating.

d When cutting the dry film (manual sticking machine), use even force to keep the trimming neat, otherwise defects such as on-line of the dry film will appear after development.

e After the film is applied, it must be cooled to room temperature before it can be transferred to the alignment process.

Fourth, exposure

1. Light energy

a Light energy (exposure tube 5000W) upper and lower lights are controlled at 40-100 mJ/cm2, use the lower drying rack to test the upper light, and the upper drying rack to test the lower light.

b. The exposure level is 9-18 levels (DuPont 25-level wedge meter), generally controlled at about 15 levels, but this level can only be reflected after development, so the development control requirements are stricter.

2. Vacuum

The vacuum degree is 85-95, and the vacuum degree is less than 85, which is easy to produce the phenomenon of faint light.

3. Hurry up

The blow-up must be at a vacuum greater than 85 and the blow-up force must be even, otherwise the pads and holes will move and cause the disk to break.

4. Exposure

Press the shutter lightly during exposure, and the panel must be taken out immediately after the exposure stops, otherwise the residual light in the lamp will be exposed for a long time, which will cause residual glue on the surface of the panel after development.

Five, development parameter control

1. Temperature 85-870C.

2. The concentration of Na2CO3 is 0.9-1.2%.

3. The spray pressure is 15-30Psi.

4. Washing pressure is 20-25 Psi for the first stage and 15-20 Psi for the second stage.

5. The drying temperature is 120-140°F.

6. Transmission speed is 40-55in/min.

6. Visual inspection

1. Common defects

a Open circuit Diazo film circuit damage.

b Short circuit The diazo film circuit is stuck with other debris.

c The exposed copper Diazo tablets are not clean.

d Residual glue There are many factors that cause residual glue. In summary, there are the following common situations.

1. The temperature is not enough;

2. The concentration of Na2CO3 is low;

3. The spray pressure is small;

4. The transmission speed is faster;

5. Overexposure;

6. Stack the board.

e-line is thin The exposure energy is high or the vacuum is low.

f On-line dry film The cutting edge of the dry film is not neat or the width of the protective edge of the diazo sheet is not enough.

g De-filming Caused by weak pasting.

2. Defect treatment measures

a Check the diazo film immediately if the circuit is open, find out the damaged part of the circuit and repair it. If it cannot be repaired, make the diazo film again. Then use a scalpel to pick open the dry film that caused the open circuit.

b. Check the diazo film immediately for short circuit, find out the debris on the line and remove it. Then the short-circuit board is repaired with a plating ink. For fine lines that cannot be repaired, the film must be removed and redone.

c. Expose the copper. Clean the diazo film immediately, and repair the exposed copper plate with electroplating ink.

d Increase the transfer speed of the remaining glue by 20-30%, immediately re-develop the remaining glue board, and find the cause of the remaining glue, check whether each parameter meets the process range, and then adjust the parameter to the range value.

e Line fine Adjust the exposure energy or check the vacuum, and redo the film of the line fine plate.

f Putting the dry film on the line Pick up the dry film on the line with a scalpel, and notify the dry film atrial cutting and alignment personnel to check the edge of the board. If the problem is found, deal with it immediately.

g Take off the film. Check the filming process parameters immediately. Black oil can be used to repair the boards that are not on the line.

Note: Open circuit and short circuit are just the opposite for etching with dry film directly as a corrosion-resistant circuit.

Seven, diazonium tablets

1. Diazo film exposure

5000W exposure lamp, exposure time 35-55S.

2. Diazo film development

Analyze pure ammonia water, temperature control 40-45 degree Celsius, develop 3-7 times until the line is dark brown.

3. Factors Affecting the Quality of Diazo Tablets and Prevention

a line thin

1. Caused by light reflection and diffraction; pure black non-reflective thick cardboard can be used for exposure under the diazo film to eliminate this phenomenon.

2. The exposure energy is too strong; appropriately reduce the exposure time.

b. Spots (commonly known as ghost images) appear after development. The exposure energy is insufficient, so extend the exposure time appropriately.

c The color is light, which is composed of the following factors

1. Insufficient temperature: wait until the adjusted temperature rises to the range value before developing.

2. Ammonia water expires: the concentration is reduced; replace the ammonia water.

3. Short developing time: re-develop 2-3 times.

4. The diazo film has a long time after exposure: the circuit part has been exposed, discarded and redone.

The above is the introduction to the PCB design and PCB production-graphics transfer process. Ipcb is also provided to PCB manufacturers and PCB manufacturing technology