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SMT Pretest Answers

  • Soldering

  • Folks,

    The SMT Pretest answers from my last post are below. How did you do?


    Dr. Ron

    Pretest Answers:

    1. What does the letter “S” in SAC stand for? Ans: S stands for tin (Sn), A for silver (Ag) and C for copper (Cu).
    2. How much silver is in SAC305? Ans: 3.0% silver, 0.5% copper and the balance tin (96.5%).
    3. What is the approximate melting point for SAC305 solder? Ans: 219ºC, but it can vary a few degrees from one solder to another due to variability of alloy concentrations, impurities, etc.
    4. Solder paste is approximately how much by weight metal? Ans: Typically about 90% by weight, or a little less.
    5. What is not a current common defect in SMT? Ans: (c.) BGA ball matting is not a defect.
      1. Head-in-pillow
      2. Pad cratering
      3. BGA ball matting
      4. Graping
    6. Which is closest to a typical stencil thickness? Ans: (c.) 5 mils (0.127 mm).
      1. 5 microns
      2. 20 mils
      3. 5 mils
      4. 20 microns
    7. Which is closest to a typical lead spacing for a plastic quad flat pack (PQFP)? Ans (c.) 0.4mm (16 mils).
      1. 0.1mm
      2. 0.1mil
      3. 0.4mm
      4. 0.4mils
    8. Which has finer solder particles, a Type 3 or 4 solder paste? Ans: Type 4.
    9. What does OSP stand for? Ans: Organic Solder Preservative or Organic Solder Protectant.
    10. Place an arrow at the eutectic point of the tin-lead phase diagram below. Ans: The blue arrow points to the eutectic point.