Introduction To The Production Process Of Flat Screen Printing
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Posted by licheng flatprinter - Filed in Business - #Hot Air Stenter Machine #Flat Screen Printing Machine Factory - 1,130 views
Wire mesh structure of Hot Air Stenter Machine
Screen, squeegee, paste, printing table, substrate
Slurry system
Silver aluminum paste: the back conductor, as the back electrode, provides solderability.
Aluminum paste: the back conductor, as the back electric field, to collect current.
Silver paste: The front conductor acts as a positive electrode to collect charges.
Influencing factors
1. The influence of printing pressure
In the printing process, the squeegee must maintain a certain pressure on the screen, and this force must be appropriate. If the printing pressure is too high, the service life of the screen and squeegee will be reduced, the screen will be deformed, and the printed graphics will be distorted. If the printing pressure is too small, the paste will easily remain in the mesh, resulting in false printing and sticking of the mesh. Increase the printing pressure within an appropriate range, the ink penetration will decrease (the wet weight of the slurry decreases), the height of the grid line will decrease, and the width will increase.
2. The influence of printing speed
The setting of printing speed must take into account both output and printing quality. In terms of printing quality, if the printing speed is too fast, the time for the paste to enter the mesh is short, the filling of the mesh becomes poor, the flatness of the printed grid line is damaged, and the gourd-shaped grid line is easily produced. The printing speed increases, the line height of the grid line increases, and the line width decreases. The printing speed slows down, the ink volume increases, and the wet weight increases.
3. The influence of the screen gap
Under certain other conditions, the relationship between the screen gap and the wet weight is roughly as shown in the figure on the right: at first the two increase almost proportionally, then the screen gap increases, the wet weight decreases, and finally it suddenly becomes zero. Screen printing uses the first half of the curve (that is, the proportionally rising section). It can be seen that the screen gap is enlarged, the amount of ink is large, and the wet weight increases. If the screen gap is too large, it is easy to distort the printed graphics; if it is too small, it is easy to stick the screen. The effect of squeegee hardness The squeegee material is generally polyurethane or fluorinated rubber with a hardness of 60-90A. The greater the hardness of the squeegee, the more accurate the printed graphics and the better the reproducibility of the original image. Therefore, the printing of the front gate line needs to choose a higher hardness squeegee. The hardness of the squeegee is small, and the wet weight is large when other parameters remain unchanged, the line height increases, and the line width becomes larger.
4. The influence of squeegee angle
The adjustment range of the squeegee angle is 45-75 degrees. The actual squeegee angle is related to the slurry. The higher the viscosity of the slurry, the worse the fluidity. The greater the downward pressure of the squeegee on the slurry, the smaller the squeegee angle. Under the printing pressure, the squeegee rubs against the screen. At the beginning of the brush, the pressure on the screen is very large. As the number of printing increases, the blade is arc-shaped, and the pressure on the unit area of the screen is significantly reduced. The actual angle of the screen is less than 45 degrees, which is easy to blur the printed lines and stick to the screen. Within the adjustable range, reduce the squeegee angle, increase the amount of ink, and increase the wet weight. The squeegee blade is blunt, the ink volume is large, and the line width is large.
5. The influence of slurry viscosity
The change of paste viscosity (thixotropy) during printing is shown on the right:
The viscosity of the paste is inversely proportional to the fluidity. The lower the viscosity, the greater the fluidity, which can ensure the quality of printing to a certain extent. The viscosity of the paste is too large, the ink permeability is poor, and orange peel and small holes are easily produced during printing. If the viscosity of the paste is too small, the printed graphics are easy to expand (the grid line expands), resulting in bubbles and burrs.
6. The influence of yarn thickness and film thickness
In general, the lower the screen mesh, the thicker the wire diameter, and the higher the paste layer after printing. Therefore, the higher the screen mesh, the lower the paste layer after printing. For screens of the same mesh, the thicker the yarn, the less ink penetration. Within a certain range, the thicker the photosensitive film, the greater the amount of ink, and the higher the printed grid lines. However, the increase of the film thickness can easily cause the photosensitive glue to fall off.
7. The influence of printing table
The levelness of the printing table: the cell is adsorbed on the printing table during printing. If the table is not flat, the cell is easy to break under negative pressure. Generally, the level of the cell should be less than 0.02mm. The parallelism between the printing table and the screen: determines the consistency of the printing paste. Generally, the parallelism between the two should be less than 0.04mm. Repeated positioning accuracy of the printing table: The repeated positioning accuracy of the solar cell printing table must reach 0.01mm.
Parameter correlation
1. Pressure and spacing: the greater the pressure, the greater the spacing; because when the pressure is high, the contact between the scraper and the screen will protrude more, if the spacing is small, the pressure on the silicon wafer will increase, and the probability of fragmentation will increase . Changing one of the two parameters without changing the other may increase the possibility of silicon chip breakage or affect printing quality.
2. The printing speed affects the production capacity, but also the amount of silicon wafer paste printed.
Adjustment of printing parameters
1. First, change the printing speed to a lower value to facilitate a good observation during debugging (for example, the printing speed is 50mm). Loosen the locking screws completely and ensure that the fixing screws on the left and right sides of the scraper and the return scraper are unlocked and can move freely.
2. First set the printing distance: the printing distance should be printed on the silicon wafer with the paste, and there is no sticky film and false printing. (Recommended: 1.5 0.3)
3. After setting the spacing, set the printing pressure. Slowly increase the pressure from low to high until the paste can be cleaned up during printing.
Parameter adjustment
4. After the pressure and spacing are set, print one piece to see if the printing is qualified, otherwise fine-tune it. (Printing speed has not been changed)
5. After the Flat Screen Printing Machine Factory is qualified, slowly turn the lock screw downwards, and lock the lock screw when you feel the lock screw just touched something. This action is equivalent to finding a limit where the squeegee drops, ensuring that the squeegee will not press down when the pressure increases.
6. Then speed up the printing speed, and measure the printing weight, if it is too large, it will slow down, if it is too small, it will speed up. (170mm is recommended).