1.Advanced packaging tasks of LED
Connecting the outer lead and the LED chip electrode, at the same time protecting the LED chip, and play a role in improving the efficiency of the drive. Key processes are frame, pressure welding and packaging.
2. LED package form
The forms of LED package are various and mainly using the appropriate size, cooling measures and the light effect based on different applications. The package forms of LED are classified as Lamp-LED, TOP-LED, Side-LED, SMD-LED, High-Power-LED, etc.
3. LED packaging process
4. Packaging Process Description
Microscopic examination: Whether the mechanical surface been damaged or lock hilled and whether the chip size and electrode size consistent with the technical requirements, and the electrode pattern is complete or not.
As the LED chips are still arranged in closely spacing after dicing and not conducive to the operation of the process. We use the expansion machine on the bonding chip to expand the film and made the LED chip spacing stretch to about 0.6mm. Manual expansion can also be used, but it is likely to cause chip broken and other undesirable issues.
Dispensing silver plastic or plastic insulation on the corresponding position of LED bracket. The difficulty of this process lies in the amount of plastic control; the colloidal height and dispensing position have detailed process requirements. It should pay attention on the action of silver plastic, mixing and the use of time, as the strict requirements of using and storage of silver plastic and plastic insulation.
Back coating is contrary to dispensing, using the back coating machine coat silver plastic on the LED back firstly and then made the LED with silver plastic on the back installed in the LED bracket. The efficiency of back coating is much higher than the dispensing, but not all products are suitable for back coating technology.
5. Hand tattoo
Placed the LED chip expanded in the stabbed fixture, and LED bracket under the fixture, with a needle to the LED chip one by one thorn to the appropriate location under the microscope. Hand tattoo has an advantage compared to automatic racking; it’s easy to replace the different chips at any time, for the need to install a variety of chip products.
6. Automatic loading
Automatic mounting is actually a combination of two steps such as dispensing and the installation of the chip, firstly the silverplastic coated on the LED bracket, and then using the vacuum nozzle suck up the LED chip and placed in the corresponding bracket position. Automatic loading in the process are mainly familiar with the equipment operation and programming, at the same time the equipment and installation of glue stick to adjust the accuracy. Bakelite nozzle should be selected as far as possible for preventing damage to the surface of the LED chip, especially blue or green chip. Because the steel nozzle will scratch the chip surface current diffusion layer.
The purpose of sintering is curing silver plastic, and the sintering temperature should to be monitored and prevent the bad batch. Silver sintering temperature is generally controlled at 150 ℃, sintering time 2 hours. According to the actual situation sintering temperature can be adjusted to 170℃, sintering time 1 hour. But the insulation glue generally 150℃, 1 hour. Silver plastic sintering oven must be required to open for replacing the sintered products every 2 hours (or 1 hour). Sintering oven shall not be used for other purposes, to prevent pollution.
8. Pressure welding
The purpose of pressure is welding lead to the LED chip and achieving the connection of internal and external lead wires. LED pressure welding process including gold wire ball welding and aluminum wire pressure welding. At first the first point should be pressured on the LED chip electrode and then pull the aluminum wire to the corresponding bracket, at last cut off the aluminum wire after the second point pressured. While it’s should burning a ball before the first point pressured during the gold ball welding process, and the rest of the process are similar. Pressure welding is the key technology in LED packaging, welding wire shape, solder joints shape and tension are should be monitored during the process. In-depth study of the pressure welding process involves a wide range of issues, such as gold wire material, ultrasonic power, pressure welding pressure, track of chopping and so on.
9. LED packaging mainly including dispensing, potting and molding.
The difficulties of process are how to control the bubbles, the lack of materials and black spots. The selection of material is the mainly design and the epoxy and stent will be better because of their good combination. Manual dispensing requires a high level of operation and the main difficulty is how to control the amount of dispensing because the epoxy will thick while using.
The package of Lamp-LED belongs to potting. The process of potting is firstly inject liquid epoxy into the LED molding cavity, and then insert the LED bracket welded, put into the oven for epoxy curing, and at last the LED will be formed out from the mold cavity.
11. Molding Package
Setting the welded LED stent into the mold, and putting the upper and lower molds together by a hydraulic press and vacuumed, then injecting the solid epoxy into the plastic molding. The epoxy went into the LED molding groove after heated and then curing.
12.Curing and post-curing
Curing refers to the curing of epoxy encapsulation, epoxy curing conditions in general 135℃, 1 hour and the molded package is typically at 150℃ for 4 minutes.
13.Post Mold Cure
Post Mold Cure is aiming to allow epoxy fully cured, while making the LED heat cured. Post Mold Cure is very important for improving the bonding strength between epoxy and stent. And the general condition is 120℃ for 4 hours.
14.Trim and Scribe
As the LED in the production is linked together, so the bars of LED should been cut by tendons. While MD-LED is in a PCB board and need a dicing machine to complete the separation work.
The photoelectric parameters of LED and external dimensions should be test according customers’ requirements for LED products sorting.
The finished product count packaging. Ultra-bright LED requires anti-static packaging