PCB Technical - Problems and solutions in the pcb proofing process

Problems and solutions encountered in PCB proofing:

Negative film is one of the important raw materials used in PCB processing plants. It works in the same way as the film used for photography, so it has high requirements for storage and use conditions. A slightly inappropriate treatment can cause many problems.

In this issue, let’s talk about some of the flaws of the negatives. Causes and elimination methods

A. Light drawing is negative

1. Problem: The negative film is foggy and the contrast is not good

(1) Old developers, the development time is too long.

Solution: Use new developers, short development time and good negative contrast (that is, good blackness).

(2) The development time is too long.

Solution: shorten the development time.

2. Problem: The edge of the negative wire is halo and the high temperature of the developer causes excessive display.

Solution: Control the temperature of the developers within the process.

3. Problem: The transparency of the film is not enough to appear foggy

(1) The fixed liquid on the precipitation of the old silver powder intensified the atomization of the film.

Solution: Replace the new repair program.

(2) Insufficient fixing time, resulting in a lack of transparency in the background color.

Solution: Keep it fixed for more than 60 seconds.

4. Problem: Insufficient cleaning of photographic film after discoloration and fixation.

Solution: After fixing, a lot of running water is needed to clean, it is best to keep it for more than 20 minutes.

B. Copy work from original tablet

1. Problem: The flipped diazo film is deformed, that is, all wires are thinner and more irregular.

(1) Improper selection of exposure parameters.

Solution: Optimize the exposure time according to the film state.

(2) The optical density of the original film did not reach the process data.

Solution: Determine the optical density so that the bright area reaches the data above Dmax4.0, and the transparent part does not need to be dense below Dmin0.2.

2. Problem: The flip of the diazonium film on the edge of the local line width is thin and irregular

(1) The process parameters of the light source of the exposure machine are incorrect.

Solution: The instrument is used to measure the energy attenuation of the UV light source lamp. If it exceeds the service life, it should be replaced.

(2) The area of the diazo film to be turned over exceeds the optimal range of the exposure frame.

Solution: According to the production situation, reduce the check area or because the light source is too close, increase the light source to an appropriate distance from the exposure table to ensure a large-size film in the large photosensitive area.

3. Problem: The total solution or local solution of the double diazonium tablets is bad

(1) The original film used is of poor quality.

Solution: Check the imaging status of the edge of the original negative line and take technical measures to improve it.

(2) The table top vacuum system of the exposure machine is malfunctioning.

Solution: Check carefully whether the air duct is perforated or damaged.

(3) There are bubbles in the negative film during exposure.

Solution: Check whether there are gray particles on the surface of the exposure machine, and check whether the film and the black paper on the exposure machine platform are dented or creases.

4. Problem: The diazo film wires that are turned over by the warp become wider, and the transparent area is insufficient (that is, the dmin data is too large). The selected exposure process parameters are inappropriate. Solution: A. Choose the appropriate exposure time.

B. The possible storage environment of diazonium tablets is close to the presence of ammonia or ammonia, leading to different degrees of development.

5. Problem: The shading area of the flipped diazo film is insufficient (DMax data is too low)

(1) When the diazo film is turned over, the development is not correct. Solution: A. Check if the developer has failed.

B. Check the ammonia supply system to determine whether the concentration is higher than '26 (that is, the specific gravity is 1.22).

(2) The original diazo sheet material is poor.

Solution: Determine whether the optical density DMax of the original film material is greater than 4.0.

6. Problem: The dimming performance of the dark area of the rotating diazo film is low dmax or even

(1) The development of flip diazo tablets is incorrect.

Solution: Check the fault status of the ammonia developer and make adjustments.

(2) The storage environment of the original film material is poor.

Solution: Store according to the specifications of the film material, especially avoid direct sunlight or close to ammonia storage.

(3) Improper operation by PCB developers. Solution: Especially to check the temperature of the developer conveyor belt, use the special sticker test for temperature and discoloration, which should meet the process requirements (non-ammonia tank in the thermostat).