PCB plate making method is divided into : -plate method, the direct and indirect -plate method, using the indirect method of the plate material were: Photographic pulp sensitive diaphragm , sensitive diaphragm , indirect film
1 -to-plate method
Methods : In a stretched good screen coating thickness of the photosensitive paste ( typically photosensitive diazonium salt slurry ) , drying the coating , plate-making film and then laminated into the exposure machine to its exposure, the developed , rinsed , after drying become a screen printing screen.
Process: Photographic pulp preparation has Stretching - skim - drying - coating - drying - exposure - development - drying - Revised Edition - Final Exposure - close up
The methods and the role of each section
Skim: use degreaser to remove grease online photosensitive paste wire and wire mesh completely glued together was not easy to stripping.
Drying: drying moisture bit avoid leaving mesh tension variation due to high temperature , the temperature should be controlled at 40 ~ 45 ℃.
Photographic pulp preparation: the photosensitizer with pure water and mix thoroughly after adding photosensitive paste Stir , place eight hours later reuse.
Film : the use gouges photosensitive paste evenly on wire-line , according to the coating into automatic and manual film coating machine coating , the coating can be based on the actual number of circumstances.
First, when the film should be coated blade surface , the purpose is first among gauze to fill the gap , to avoid air bubbles, then was coated printing surface ( in contact with the PCB side ) , currently used automatic coating machine for each coating one can increase the thickness of approximately 3um, so most of the solder stencil coating method chosen : two blade surface coating - drying - three times the printing surface coating - drying - the printing surface coating three times - drying - three times the printing surface coating - drying.
Coating methods are wrong description :
A. correct blade surface coating , the thickness of the printed surface suitable to meet the requirements .
B. thin film ( printing surface ) Disadvantages: poor durability .
C. scraper surface coating is too thick Disadvantages : Due to the blade surface of the photosensitive paste is too thick , the photosensitive uneven when developing water after washing, the surface roughness of ink poured into the film , making the film off, resulting stencil life cut short .
D. scraper surface coating is too thin Disadvantages: poor durability .
Drying : Drying the photosensitive paste evenly , avoiding the sensitive pulp dry wet outside , the outside temperature will be dry and inside photosensitive paste is dry , leaving the screen life cut short , the temperature should be maintained at 40 "45 ℃, time 10 minutes, depending on the thickness of the drying time adjustments .
Exposure: proper exposure can photosensitive paste photopolymer through negatives developing a clear image .
Factors affecting the quality of the screen :
A. correct exposure energy
B. The exposure and the degree of vacuum
C. Exposure glass cleaner
General exposure energy used to adjust the exposure time , the production should be based on screen mesh thickness by using graded exposure method using the exposure estimates to determine the various types of network version of the film proper exposure time.
Calculation sheet to use:
① exposure time in advance plus twice the estimated exposure time , the developing normal way , choose the best , i.e., the clear image in the range of a post- development, the actual exposure time is then multiplied by the selected the image scale factor , is the preferred exposure time.
There are five factors on estimates films, namely: 1.0,0.7,0.5,0.33,0.25 , the coefficients corresponding to a circular target graphics and outlets.
② such factor appears to be the best coefficient of 1.0 , will have to just double the exposure time together , re -plate exposure test .
③ such as coefficient of 0.25 seems to be the best coefficient , will have to reduce by half the exposure time just to re -plate exposure test .
Several factors such as continuous ④ are met, the upper limit of the smaller coefficient using dot pattern when the sun , that some of the exposure time is shorter , the sun generally used when a higher limit than the broad-brush factor , namely the partial exposure time longer .
⑤ several factors are met , such as continuous according to the type of screen proofing , the finest selection of the target line or circle dot sharpness choose the best coefficients.
Further , the backsheet dense paste , glass cleaner exposure machine , the vacuum pump has an important impact on both the quality of copy .
Development : the use of water-soluble photosensitive paste features , the use of water will not wash away the exposed photosensitive paste , developing ways has great influence on the fine screen , you must spray before developing the photosensitive aqueous slurry sucked up ahead , standing one . " 2 minutes , then fanned back and forth developing water cannons until the image is completely clear.
Note : High-pressure washing can not leave the screen too , generally 0.8 "1m, otherwise too much pressure so easy to produce jagged lines , serious part of the network is obliterated .
Drying : The online version of the moisture dry, the temperature is not too high, otherwise it will produce change screen tension , usually 40 "45 ℃.
Revised version , check : to repair and inspection of pinholes and some NPTH hole.
Finally Exposure: Photographic pulp and further improve the adhesion of gauze , increase service life.
Close up : The data on pulp fills the screen spare part , so as not to leak ink when printing.
⑵ sensitive diaphragm -plate method
Process: has Stretching - skim - wet - film - drying - Reinforcement - exposure - development - drying - Revised version - close up
Method
Photographic film diaphragm commonly known as water , is 0.1mm thick transparent plastic film for film base , Bing coating on its side of the emulsion layer of a certain thickness made fully wet when using the first screen , then paste film sheet diaphragm is adsorbed by capillary action to the wire-line , remove the plastic film base and dried is exposed and developed , to give the final desired pattern .
Wet : use of a wetting promoting uniform water film is formed on the surface of the screen so that a smooth transfer of the photosensitive film .
Film : According to the halftone type photosensitive film onto the blade to the surface of the wet screen , paste after scraping the excess water with a spatula .
Drying: Drying generally below 40 ℃, after drying to remove the plastic film base , and dried to a few minutes more .
Reinforcement : To increase the number of printing plates can be dried in the diaphragm blade topcoat layer of photosensitive paste, to be dried after coating .
Consistent with other parts of the operation and the plate photosensitive paste method .
2 , the direct and indirect -plate method
Method
Direct and indirect method is when the plate is first coated with a photosensitive plate wrist film base material of the photosensitive film on the flat face on the work surface , a good wrist stretched flat on the screen frame onto a substrate , and then placed in the screen frame photographic pulp and coated with a soft squeegee pressure , drying fully unfold the plastic film base , attached to the photosensitive film can be used for wrist screen copy, by developing , after drying the silk screen .
Process:
Has Stretching - skim - drying - stripping film base - exposure - development - drying - Revised version - close up
3, the indirect method of the plate
Method
The indirect method is to plate indirectly exposed first film after curing with 1.2% H2O2 developed with warm water , dried and graphics into a peelable film, the film surface of the graphic film in close contact with the screen stretched well plate by squeeze to make the film with moist paste screen real , peeled off the film base , made of silk with the wind and dry on the screen .
Process:
1 has Stretching - skim - Drying
2 Indirect film - Exposure - hardening - developing
1and2 - fit - dry - Revised version - close up
