LED package Collection: LED packaging technology can not know the knowledge(II)
Second, the packaging process
1, LED package of the task
Is to connect the outer lead to the LED chip electrode, while protecting the led chip, and play a role in improving the efficiency of light extraction. Key processes are mounting, welding, packaging.
2, LED package form
LED package can be said to be a wide variety, mainly according to different applications using the appropriate size, cooling measures and light effects. Led by package in the form of Lamp-LED, TOP-LED, Side-LED, SMD-LED, High-Power-LED, and so on.
3, LED packaging process
A) Chip inspection
1, Whether there is mechanical damage to the surface of the material and linen pit (lockhill);
2, Chip size and electrode size is consistent with the process requirements;
3, The electrode pattern is complete.
B) Expanded tablets
As the LED chip after the scribe is still arranged in close spacing is very small (about 0.1mm), is not conducive to the operation of the process. We use the expansion of the film on the adhesive chip expansion, LED chip spacing is stretched to about 0.6mm. You can also use manual expansion, but it is likely to cause the chip fall and waste and other undesirable problems.
In the corresponding position of the led stent silver glue or plastic.
(For GaAs, SiC conductive substrate, with the back electrode of the red, yellow, yellow and green chip, using silver plastic. For sapphire insulating substrate blue, green led chip, using insulating glue to fix the chip.) Is the amount of dispensing control, in the colloid height, dispensing position has a detailed process requirements. As the silver plastic and insulating plastic in the storage and use are strict requirements, silver plastic wake material, mixing, the use of time is the process must pay attention to matters.
D) Preparation of glue
And dispensing on the contrary, the preparation of rubber is prepared with a plastic machine on the back of the silver paste on the back electrode, and then put the back with silver plastic led on the led bracket. The efficiency of the glue is much higher than that of the dispensing, but not all products are suitable for the preparation process.
E) Hand thorns
Will be expanded after the LED chip (with glue or not prepared) placed in the jaw table on the fixture, LED bracket placed under the fixture, under the microscope with a needle to the LED chip one by one to the appropriate position. There is a benefit compared to manual loading and automatic mounting, making it easy to replace different chips at any time for products that require a variety of chips.
F) Automatic loading
Automatic loading is actually a combination of sticky glue (dispensing) and the installation of the chip two steps, first in the led bracket on the silver plastic (insulation), and then use a vacuum nozzle will suck the chip sucking mobile position, and then placed in the Corresponding to the stent position.
Automatic loading in the process mainly to be familiar with the equipment operation and programming, while the equipment of the glue and installation accuracy to adjust. In the selection of the nozzle on the choice of bakelite nozzle, to prevent damage to the surface of the led chip, especially blue, green chip must be bakelite. Because the steel mouth will scratch the chip surface current diffusion layer.
The purpose of sintering is to soften the silver paste, sintering requirements to monitor the temperature to prevent the poor batch.
Silver sintering temperature is generally controlled at 150 ℃, sintering time of 2 hours. According to the actual situation can be adjusted to 170 ℃, 1 hour. Insulating rubber is generally 150 ℃, 1 hour. Silver plastic sintering oven must be in accordance with the process requirements of 2 hours (or 1 hour) to open the replacement of sintered products, the middle shall not be free to open. Sintering oven can not be used for other purposes to prevent contamination.
The purpose of welding lead to lead the chip led to complete the product inside and outside the lead connection work. LED welding process has gold wire and aluminum wire welding two. The right is the process of aluminum wire bonding, the first LED chip electrode pressure on the first point, and then pull the aluminum wire to the appropriate bracket above, press the second point after the break aluminum wire. The gold bullion process burns the ball before the first point of pressure, and the rest is similar.
Pressure welding is the key link in LED packaging technology, the main need to monitor the process is the pressure welding wire (aluminum wire) arch wire shape, solder joint shape, tension. In-depth study of the welding process involves a wide range of problems, such as gold (aluminum) wire material, ultrasonic power, pressure welding pressure, chopper (steel) selection, chopper (steel) movement trajectory and so on. (The following figure is under the same conditions, two different splitters out of the solder joint micro-photos, both in the micro-structure differences, thus affecting the quality of the product.) We are no longer tired here.
LED packaging is mainly a little plastic, potting, molding three. Basically, the difficulty of process control is the bubble, more than material, black spots. Design is mainly on the selection of materials, use a combination of good epoxy and stent. (General LED can not pass the air tightness test) as shown in the figure TOP-LED and Side-LED for dispensing. Manual dispensing package on the operating level is very high (especially white LED), the main difficulty is the amount of dispensing control, because the use of epoxy in the process will become thicker. White LED dispensing there is also the phenomenon of phosphor powder precipitation caused by the color difference.
J) Glue package
Lamp-led package in the form of potting. Potting process is the first in the led molding cavity injection of liquid epoxy, and then insert a good welding led bracket, into the oven to epoxy curing, the led from the mold out of the molding.
K) Molded package
Will be welded with a good led bracket into the mold, the upper and lower mold with a hydraulic press mold and vacuum, the solid epoxy into the injection of the entrance of the hydraulic pressure into the mold with the hydraulic plunger into the mold, epoxy cis The plastic road into the various led into the groove and curing.
L) Curing and post curing
Curing is the encapsulation of epoxy curing, generally epoxy curing conditions at 135 ° C for 1 hour. The molded package is typically at 150 ° C for 4 minutes.
M) After curing
After curing is to make the epoxy fully cured, while the heat for the led aging. Post-curing is important for improving the bonding strength between epoxy and stent (PCB). The general conditions are 120 ° C for 4 hours.
N) cut bars and scribes
As led in the production is connected together (not a single), Lamp package led with cut cut off the support of the ribs. SMD-led is in a PCB board, the need for dicing machine to complete the separation work.
Test led the photoelectric parameters, test the size, at the same time according to customer requirements for LED products sorting.
The finished product is packed in count. Super bright LED need anti-static packaging.