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Everwide Newsletter No.229

Experiment § Why does the LED change color after being filled with epoxy resin?

SMD-type LED applications are often filled with epoxy resin to protect the entire module and prevent moisture from corroding the circuit. Sometimes after the epoxy resin is hardened, it is found that the light color of the LED is different, some are white, and some are yellow (Figure 1). This situation is often caused by the epoxy resin not wholly covering the surface of the LED. As long as the epoxy resin is dropped on the yellowish LED, the color will return to normal (Figure 2). This phenomenon is because the blue light chip hits the yellow phosphor and emits white light. If the epoxy resin above the LED does not entirely cover the luminous area, some light will be reflected in the LED. When the white light hits the yellow phosphor, it will be dyed yellow and then reflected, so the color is yellowish. Some LEDs initially emit white light, but after the ring test and the upper resin peel off, after the interface between the two is formed, the white light will be reflected downward back to the LED, and the light will turn yellow when it is reflected again (Figure 3).

─ Author: Miss. Su-huan, Li


Activity § Site environment improvement - cooling down

In recent years, the temperature has become higher and higher, and the manufacturing department's production sites have become more and more sultry. Everyone often sweats and feels uncomfortable while they are working. Therefore, it is urgent to improve the temperature of the on-site working environment. Every year, we try our best to improve, such as: sticking heat insulation paper, making ceilings, setting sunshade nets, etc. This year, we will focus on the direction of airflow and strengthen the one-in-one-out effect. We first installed 6 exhaust fans above the roof and used baskets as air ducts to exhaust the factory's hot air. At present, the mixing chamber's temperature has dropped significantly by 2 to 3 degrees, and the initial cooling effect has been achieved. In the next stage, we will think of ways to lower the air temperature entering the factory so that our colleagues can work in a comfortable environment.


Knowledge § There is condensation on the mirror surface of the optical parts. What is the reason?

There are three liquid sources similar to water droplets on the mirror surface: (1) The part of the adhesive used. For example, Epoxy resin has a volatile matter at high temperature, condensed on the mirror surface. To determine whether it is caused by the adhesive, just put the adhesive in a glass bottle, seal and heat, and see if there is any volatile condensation. (2) The part of plastic material absorbs moisture. Many plastic materials themselves absorb moisture in the air and have a certain percentage of water absorption. As long as the plastic is preheated to remove water and then made into parts and observed, it can be proved whether the material absorbs moisture. These two possibilities can also be detected by the weight change of epoxy resin or plastic material before and after baking. (3) The natural humidity in the air when packaging parts. This phenomenon will condense when the temperature is low and disappear when the temperature is high. Encapsulation in a humidity-controlled environment, or placing a desiccant in the parts, can eliminate the influence of air humidity.


Living § Japanese consumer experience

When I traveled to Okinawa for the first time, I found that the Japanese were very polite about handling "money." When shopping at the supermarket, the clerk helped to pack and scan the barcode. When he wanted to check out, please put the money in the cash register next to it. The cash register will eat the banknotes and find the change. The clerk does not have to worry about counting the wrong banknotes, finding the wrong money, getting fake banknotes, etc. To eat at a ramen shop on the side of the road, you first buy a ticket with a vending machine and then show the ticket to the clerk. The clerk does not receive cash; he cooks and delivers meals to the customers, avoiding contaminating food. Even if you pay face-to-face and hand the banknotes to the clerk, the clerk will not check the banknotes one by one. They trust the customers and give them great respect. When dining in the restaurant, the service staff will deliver the menu after the guests are seated, and then inform the guests if they need to order, then press the service bell. During this period, you can look at the menu, and no one will disturb you. Until you decide on your meal, ring the bell and ask the service staff to order. It is very different from Taiwan. Will Taiwanese people care about the customer's menu very enthusiastically? When do you want to order? If there are so many customers, the service staff will be so busy, so you can't find them. It becomes the guests are looking for waiters and raise their hands at any time. The Japanese restaurant saves unnecessary communication time, the service staff does not need to wait for the customer to think, and the customer does not have to spend any effort to find a waiter. A small design can meet the needs of both parties. Pay attention to the details and etiquette of life, making people relaxed and comfortable. It is worth learning for anybody.

─ Author: Mr. Hui-xu, Li


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