Silk screen printing

The screen printing process of solar cells USES the screen printing method to complete the production of back field, back electrode and positive grid wire metal electrode, so as to lead out the generated current.The screen printing process has three purposes.

1) Electrode printing is carried out on the silicon wafer behind the P-N junction and $film.

2) The carrier generated by the light can be successfully exported to realize photoelectric conversion of solar cells.

3) Sintered and dried the slurry on the silicon wafer, and burned up the organic components of the slurry to form a good ohmic contact between the slurry and the silicon wafer.

Screen printing equipment

1) Screen printing line.

The solar cell screen printing equipment is composed of the upper part, three printing heads, two drying stoves and transmission parts.Three print head, respectively, in turn, to complete the back electrode, electric field and the positive electrode printing, after complete the back electrode and the back field of printing is to enter the drying oven drying processes, for the back of the printing process, upon completion of the positive electrode printing, directly through the conveyor belt transmission into the sintering furnace, complete drying sintering process.

2) Electronic platform scale.

In screen printing process, two electronic platform scales with precision of 0.01g are needed to monitor the weight gain of silicon wafer after printing.

Electronic balance is the latest generation of balance, according to the principle of electromagnetic force balance, direct weighing, the full range does not need weights.After placing the weighing object, the balance is reached within a few seconds, and the reading is displayed. The weighing speed is fast and the accuracy is high.The supporting point of electronic balance is replaced by elastic reed, the agate blade of mechanical balance is replaced by differential transformer, and the pointer scale type is replaced by digital display.Therefore, the electronic balance has the characteristics of long service life, stable performance, simple operation and high sensitivity.

3) Paste mixer.

In screen printing, must be a period of time for the new slurry mixing, through stirring, make the slurry mixed evenly, there is no caking phenomenon, in order to better printing process.

Screen printing process and its parameters

The process flow of screen printing is very intuitive, and the main processes are basically completed in the visible range of silicon wafers.However, the screen printing process on the quality of the operator is relatively high requirements, requirements operators have skilled equipment experience, especially in the printing process, the printing head setting, adjustment requirements are high, and need to add slurry more frequently.Screen printing process mainly has the following – some points to pay attention to.

1) Formulation of process parameters — printing pressure, printing height, printing and feeding speed, screen selection, sizing selection, etc

2) Control of printing size

3) Control the uniformity and integrity of printed graphics

4) Screen graphics and diffusion process coordination

5) Yield control — process stability control

Precautions for printing

1) Screen printing attention points

A. If debris occurs in A certain link, press the “Stop” button on the operation panel of the corresponding printing press immediately, and inform the front printing to Stop together with the oven.After disposing of the debris, restart production.Debris handling shall be carried out in accordance with debris handling standards.

B. Monitor the operation and printing quality at any time.Press the “Stop “button of the corresponding printing press in case of special situation and deal with it accordingly.

C. Printing quality shall be measured by clear and tidy line boundaries and even and smooth slurry.

D. When the printed silicon wafer sticks to the screen, press the “Stop “button on the left operating panel of the corresponding printing machine immediately, open the printing head, and take out the silicon wafer.

2) Points of attention in fragmentation processing

A. Pick up large silicon wafers and vacuum cleaner to remove small silicon chips and micro silicon powder when the chips are generated on the production line.

B. It is strictly prohibited to blow away the powder by mouth under any circumstances.

C. When dealing with debris, the equipment shall be stopped, and the production shall continue after the site is cleaned up and the fault is removed.

However, it can also be handled while the equipment is running under the condition of ensuring the safety of the person and equipment.

3) Pay attention to the use of slurry

A. Slurry must be stirred before use, silver slurry and silver aluminum slurry shall be stirred for more than 6 hours, and aluminum slurry shall be stirred for 2-3 hours.

B. See clearly the paste used in this process before use, and do not add mistakes.

C, paste bottle should be cleaned before and after use, paste scraper do not mix, to avoid paste pollution.

4) Screen use points of attention

A, the use of tensiometer screen before the use of tension, tension is lower than 18N can not be used for production, grid wire screen printing more than 8000 pieces after the need to replace.

B, screen plate use light handle light, avoid contact with sharp objects, printing shovel size also want to be light, avoid knife cut screen.

C. Dry paste on the printing machine cannot be cleaned during printing to prevent blocks of paste from falling off and blocking the screen.

D. After use, carefully clean the paste on the screen with a spade knife, and flush the screen with alcohol to ensure that no net is blocked and then wipe dry with a dry dust-free cloth.Put it in the screen cabinet.

E, graphics incomplete, tension does not meet the requirements and other reasons can no longer use the screen should be marked with eye-catching labels, and timely clear out of the production line, please indicate that can not use the screen, the operator should not be in use.After wiping the screen, such as the occurrence of continuous sticky film notification process.

2, in the process of printing production, sometimes printing graphics are not complete, at this time should check whether the screen is blocked, such as blocking with a dust-free cloth to wipe clean.Whether scraper and recharging knife are installed smoothly, if not, reinstall smoothly.Whether the scraper is damaged and whether there is foreign matter in the slurry, such as the scraper is damaged need to replace the scraper, such as there is foreign matter in the slurry, replace the slurry.

3. Under normal printing appearance, two pieces of silicon wafers (200 pieces) should be taken for testing to measure the weight gain of each printing track. Refer to the middle value in table @ above.