#1-LED LEAD FRAME
Part - 2
Material Selection 2: Synthetic Resin
At present, PPA, PCT and EMC are among the most commonly used materials. PPA and PCT are thermalsoftening1 plastics, while EMC (mainly made from of epoxy) is thermosetting2. EMC ranks first in temperature tolerance among the three. PPA offers inferior properties compared to the other two in temperature tolerance, yellowing resistance and air-tightness, yet it has the most appealing price.
Due to different abilities to dissipate heat, these three materials are applied for different specifications. PPA is used for 0.1-0.2W LED lights, and PCT for 0.8W lights, EMC for 3W lights.
As a lead frame material, EMC bears excellent properties of heat resistance, yellowing resistance, high current, high power, high density, UV resistance and small size. An increasing number of EMC packaging production lines are being established by manufacturers who believe that EMC is the new future for LED packaging.
1: A thermosoftening plastic is a plastic polymer that becomes moldable above a specific temperature and solidifies upon cooling.
2: A thermosetting plastic is a plastic polymer that strengthens during being heated, but cannot be remolded or reheated after its initial heat-forming.
Aging test comparisons among EMC, PCT and PPA at 85℃
When we talk about plastic materials, there is another issue you should pay attention to: recycled materials.
Resin manufacturing produces leftover materials that are recyclable. After stages of high temperature melting and molding, they are reprocessed and reused by many manufactures. This is called Shuikouliao ( "水口料" ) in Chinese market. Some manufacturers replace raw materials partly with the re-processed leftovers, yet alleging that they use purely raw materials.
Well, the story’s not over here. After repeated use, the recycled materials get recycled again by some manufacturers. They mix them with other glass or mineral fibers, and then granulate them into shapes that look almost the same as purely raw materials. They, again, are used to replace raw materials. These granules are called Chouliliao ( "抽粒料" ) in China.
Experiments has repeatedly established that Shuikouliao and Chouliliao (recycled materials) have compromised reliability. First-time recycled materials might have an acceptable performance that suits for low-end market, but re-granulated ones show much greater diminishments. The latter has lower intermolecular bonding force, greater and faster late-stage yellowing and light degradation. Some manufacturers will even add titanium dioxide for the brightness, in which case the light is sufficiently bright at first but then quickly gets dimmer.