The optoelectronic coupler usually adopts DIP package or SMD package. The practical process: package the infrared LED and the silicon photosensitive triode, then form the input/output pins. This process is similar to IC package, but the difference is about the material selection and key process control. Usually, the manufacturing process of the optoelectronic coupler is as following:
Ceramic base production→Thick film circuit production→Chip (IR LED, PD and ASIC) test→Chip sintering and pressure welding→Medium test→Coupling alignment→Loading rack→Packaging→Leak hunting→Medium test→Burn-in screen→Final test.
In accordance with the process, through the analysis of defective products in the production of an optical coupler
, combining characteristics of the optoelectronic coupler, the industry summarized the technological factors that affect the optoelectronic coupler's reliability:
1. The influence of silver glue
We used the silver slurry process when loading rack so that the chip can have a good ohmic contact and a low forward voltage drop. But the cohesive force is different between different brand silver glue and various chip materials and rack. Moreover. There is much difference in storage and service life, too. The improper use can cause bad cohesive force between chip and rack, bonding and even film-dropping.
2. The influence of hand work loading rack and bonding quality
Because the length and width of infrared chips are only 0.3mm, and the material is fragile, it is easy to have quality problems in the hand work loading rack. Consequently, it is common to use automatic rack die bonders.
3. The influence of internal package and injection molding external package
When the optoelectronic coupler is fluid dispensed in the internal package, if the needle comes into contact with the gold wire, there will be bad situation such as false welding, broken wire, and back-wire in the glue. Because the elasticity of internal package materials is good, defective products are difficult to be filtrated completely. It will affect product reliability. In addition, there is much heat-match difference between internal package materials and plastic materials. So, the two combined is not very close when the external package is done. In the optoelectronic coupler structure, the bonding section between plastic-coating body and rack is small, so the strip will be deformed during packaging and sticking. The inner plastic-coating body is not solidified completely during rapping, so there will be gap when it is stressed, which causes the looseness of the pin. Then the rosin joint will be snapped at wire rack by the inner lead to form intermittent open circuit. Therefore, it can improve the product sealing and device stability by selecting plastic sealing material with a good bonding performance and wire rack, and improve the process to eliminate the break of inner leads during package.