Since 2000, with the rapid development of LED light sources, the flexible LED strip has been widely adopted for both outdoor and indoor decoration as well as entertainment places. The interior advantages of LEDs enable them to quickly replace neon lights and incandescent lamps. The technology of LED chips becomes more and more mature, which further guarantees the excellent performance of the flexible LED strip. Encapsulation is a fairly essential step during the manufacturing of LED products, which determines their price and quality to a certain degree.
The LED encapsulation seals the diode chip inside the capsule and connects the outer lead with the electrode of LED chips. Thus it could protect the normal working of chips and improve the light extraction efficiency. Generally there are resin encapsulation and silicone encapsulation, and the former is cheaper because the heat dissipation is not very good. The resin could work as lens. After encapsulation, the viewing angle of the flexible LED strip is smaller than before, and the brightness is also improved.
There are various encapsulation methods of LED products: Lamp-LED, TOP-LED, Side-LED, SMD-LED, and high-Power-LED. According to the working environment, we adopt different appearances, heat dissipation methods as well as luminous effects. We strictly control every manufacturing step of the flexible LED strip, and following are the detailed explanation:
1. Check the chips: we adopt microscopic examination. Check the surface of LED chips to see whether there are mechanical damages or pits, whether the size of electrodes meets technological requirements, and whether the electrode pattern is complete.
2. Expand the chips: after scribing, the LED chips are still arranged closely (the intervals are only about 0.1mm), which is not convenient for following procedures. We adopt the expansion piece machine to expand the membrane of bonding chips and enlarge the intervals to 0.6mm. We do not adopt manual expansion during the manufacturing of the flexible LED strip because it may cause the dropping of chips.
3. Dispensing: we dispense elargol or insulating cement on the LED frame. It is difficult to control the quantity of the cement, and we have strict technological requirements upon the height and location of the colloid. The storage and applications of the elargol and insulating cement should be strictly controlled, and we should pay much attention to the waking, mixing, and using time of the elargol when manufacturing the flexible LED strip.
4. Glue preparation: different from dispensing, glue preparation should spread the elargol on the backplate of the LEDs. Then we will install the LED on the LED frame. The efficiency of glue preparation is far better than dispensing. However, not all products could adopt glue preparation technology.
5. Manual thorn-chip: put the expanded LED chips on the fixture of the thorn light table. Under the microscope, we stab each chip to respective locations with needles. Manual thorn-chip and automatic racking have an advantage: we can replace different chips whenever we need, so it is suitable for the special flexible LED strip which adopts multiple kinds of chips.
6. Automatic racking: it actually includes two steps: dispensing and installing chips. First we need to dispense elargol (or insulating cement) on the LED frame, and then move LED chips with suction nozzles to respective locations. We’d better select the suction nozzles made of Bakelite, which will not damages the surface current spreading layer of LED chips.
7. Firing: it aims to solidify the elargol. This process has strict requirements upon the temperature, which could be around 150°C (it could be adjusted to 170°C according to the actual situation). This process needs 2 hours (it could be adjused to 1 hour). For insulating cements, it should be 150°C and 1 hour. The owen should be opened every 2 hours or 1 hour to replace products. The owen could not be used for other purposes to avoid pollution.
8. Pressure welding: the aim is to connect the electrode with LED chips. There are two kinds of pressure welding: gold ball bonding and aluminum wire bonding. It is the key procedure of the encapsulation of the flexible LED strip.
9. Dispensing encapsulation: there are mainly three encapsulation methods: dispensing, glue pouring, and mould pressing. Basically, difficulties exist in air bubbles, excessive incomplete fillings, and black spots. The control of glue is very difficult, because the epoxy may become dense during using. The dispensing of the white flexible LED strip may also cause chromatic aberration resulted from the sediment of fluorescent powders.
10. Glue pouring encapsulation: lamp-LED often adopts this method. First we inject the liquid epoxy inside the LED forming block and then insert the LED frame. Put the device inside the oven for solidification. Finally, the LED will be shaped out of the mould cavity.
11. Mould pressing encapsulation: put the LED frame after bonding inside the mould. Combine the two moulds together and extract the air between them. Heat solid epoxy resin at the entrance of the glue channel and then press it with the hydraumatic mandril. The epoxy will enter each molding slots and then solidify.
12. Curing: it refers to the solidification of the epoxy resin. Generally it needs 135°C and one hour. Mould pressing encapsulation needs 150°C and 4 minutes. Curing and post-curing are two related steps during the production process of the flexible LED strip.
13. Post-curing: curing is to completely solidify the epoxy resin and adopt thermal ageing for LEDs. The post-curing is very important to improve the bonding strength of the epoxy resin and frame. Generally, this process needs 120°C and four hours.
14. Trimming and scribing: as LEDs are connecting together during manufacturing, we need to cut the uncut dambar of the LED frame. SMD-LED is different: it is arranged on a PCB board, and we need a scribing machine to separate them.
15. Test: we will test the photoelectric parameters of the flexible LED strip and check the appearance of the product. At the same time, we will also classify the LED products according to specific demands.
16. Package: finally we count and pack the end product—the flexible LED strip. Super bright ones should adopt anti-static package materials.
In this passage, we explain clearly the encapsulation process of the flexible LED strip, which is a delicate work. During the encapsulation, we should pay much attention to the static electricity, which may cause the failure of the whole strip light. Our company also adopts strict tests before leaving the factory. Our aim is to provide the best products as well as services for you.
