A&Q of PCB (2)

  • 2021-10-08 18:10:52
9. What is resolution?
Answer: Within a distance of 1mm, the resolution of the lines or spacing lines that can be formed by the dry film resist can also be expressed by the absolute size of the lines or spacing. The difference between the dry film and the resist film thickness The thickness of the polyester film is related. The thicker the resist film layer, the lower the resolution. When the light passes through the photographic plate and the polyester film and the dry film is exposed, due to the scattering of the light by the polyester film, the lighter side Seriously, the lower the resolution.

10. What is the etching resistance and electroplating resistance of PCB dry film?
Answer: Etching resistance: The dry film resist layer after photopolymerization should be able to withstand the etching of iron trichloride etching solution, persulfuric acid etching solution, acid chlorine, copper etching solution, sulfuric acid-hydrogen peroxide etching solution. In the above etching solution, when the temperature is 50-55°C, the surface of the dry film should be free of hair, leakage, warping and shedding. Electroplating resistance: in acidic bright copper plating, fluoroborate ordinary lead alloy, fluoroborate bright tin-lead alloy plating and various pre-plating solutions of the above electroplating, the dry film resist layer after polymerization should have no surface hair , Infiltration, warping and shedding.

11. Why does the exposure machine need to suck a vacuum when exposing?

Answer: In non-collimated light exposure operations (exposure machines with "points" as the light source), the degree of vacuum absorption is a major factor affecting the quality of exposure. Air is also a medium layer. , There is air between the air extraction film, then it will produce light refraction, which will affect the effect of exposure. Vacuum is not only to prevent light refraction, but also to prevent the gap between the film and the board from expanding, and to ensure alignment /The quality of the exposure.

12. What are the advantages of using volcanic ash grinding plate for pretreatment? shortcoming?
Answer: Advantages: a. The combination of abrasive pumice powder particles and nylon brushes is tangentially rubbed with cotton cloth, which can remove all dirt and expose fresh and pure copper; b. It can form a completely sand-grained, rough and uniform D. The surface and the hole will not be damaged due to the softening effect of the nylon brush; d. The flexibility of the relatively soft nylon brush can make up for the The problem of uneven plate surface caused by brush wear; e. Since the plate surface is uniform and without grooves, the scattering of exposure light is reduced, thereby improving the resolution of imaging. Disadvantages: The disadvantages are that the pumice powder is easy to damage the mechanical parts of the equipment, the control of the particle size distribution of the pumice powder and the removal of the pumice powder residue on the surface of the substrate (especially in the holes).

13. What effect will the circuit board developing point be too large or too small?
Answer: The correct development time is determined by the development point (the point where the unexposed dry film is removed from the printed board). The development point must be maintained at a constant percentage of the total length of the development section. If the developing point is too close to the outlet of the developing section, the unpolymerized resist film will not be sufficiently cleaned and developed, and the resist residue may remain on the board surface and cause unclean development. If the developing point is too close to the entrance of the developing section, the polymerized dry film may be etched by Na2C03 and become hairy due to prolonged contact with the developing solution. Usually the developing point is controlled within 40%-60% of the total length of the developing section (35%-55% of our company).

14. Why do we need to pre-bake the board before the characters are printed?
Answer: The pre-baked board a is to enhance the bonding force between the board and the characters before the characters are printed, and b to enhance the hardness of the solder mask ink on the surface of the board to prevent the solder mask oil cross-spreading caused by the character printing or subsequent processing.

15. Why do we need to swing the brush of the pre-treatment plate grinding machine?
Answer: There is a certain distance between the brush pin reels. If you don’t use the sway to grind the plate, there will be many places that will not be worn, resulting in uneven cleaning of the plate surface. Without swaying, a straight groove will be formed on the plate surface. Causes wire breakage, and it is easy to break holes and produce tailing phenomenon without swinging the edge of the hole.

16. What effect does the squeegee play on printing?
Answer: The angle of the squeegee directly controls the amount of oil, and the uniformity of the blade to the surface directly affects the surface quality of the printing.

17. What are the effects of solder mask and temperature and humidity in the darkroom on PCB production?
Answer: When the temperature and humidity in the darkroom are too high or too low: 1. It will increase the garbage in the air, 2. The film sticking phenomenon is easy to appear in the alignment, 3. It is easy to cause the film to deform, 4. It is easy to cause the board surface to oxidize.

18. Why don't solder mask be used as a developing point?

Answer "Because there are many variable factors in solder mask inks. First of all, the types of inks are more and more complicated. The properties of each ink are different. During printing, the thickness of each board ink will cause uniformity due to the influence of pressure, speed and viscosity. They are not the same as the dry film. The thickness of the single film is more uniform. At the same time, the solder resist ink is also affected by different baking time, temperature, and exposure energy during the production process. The effect of the board is the same. So the practical significance of solder mask as a development point is not great.

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