Packaging and assembly

Why are the molding compounds of many plastic packages black?

  1. ATo reduce the resin's strength
  2. BTo block light, preventing carriers generated in the chip by light from causing malfunctions
  3. CTo absorb heat and warm the chip
Show answer and explanation

Answer: B. To block light, preventing carriers generated in the chip by light from causing malfunctions

Silicon generates electron-hole pairs when it absorbs light (the photoelectric effect), so light increases leakage current and can cause malfunctions. Carbon black or similar is added to the molding compound to make it black and block light. This also makes markings easier to read.

  • A. It is not intended to reduce strength.
  • B. Correct. It prevents light-induced malfunctions.
  • C. It is not intended to warm the chip.
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More Packaging and assembly questions

  1. In high-pin-count BGA packages, why are many of the balls assigned to power and ground?
  2. In wire bonding that forms a ball, where is the first bond (ball bond) generally made?
  3. What is the main purpose of heating packages in an oven for some time after molding (post-mold cure)?
  4. What is the defect called in which bonding wires are pushed aside and deformed by the resin flow during molding?
  5. What change occurs when the temperature of a molding compound exceeds its glass transition temperature (Tg)?