Packaging and assembly

What change occurs when the temperature of a molding compound exceeds its glass transition temperature (Tg)?

  1. AThe resin becomes a metal
  2. BThe resin becomes transparent
  3. CThe thermal expansion coefficient increases and the elastic modulus drops
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Answer: C. The thermal expansion coefficient increases and the elastic modulus drops

Above its glass transition temperature, the resin changes from a hard glassy state to a soft rubbery state, its thermal expansion coefficient rises sharply and its modulus drops. Because this changes the stress from thermal expansion mismatch with the chip and leadframe, it is an important property in package reliability design.

  • A. The resin does not become a metal.
  • B. It does not become transparent.
  • C. Correct. The expansion coefficient rises and the modulus falls.
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More Packaging and assembly questions

  1. Which method makes very thin chips by first cutting grooves partway into the wafer from the front and then grinding the back to separate the chips?
  2. In dense assemblies such as smartphones, what is the purpose of forming a metal film on the package surface by sputtering or similar?
  3. In reflow, what is the defect called in which one end of a small part such as a chip resistor lifts up so the part stands on end?
  4. What is the defect called in which the force or ultrasound of wire bonding cracks the insulator or silicon beneath the bond pad?
  5. Which correctly describes wire bonding?