The SMT Pretest answers from my last post are below. How did you do?
- What does the letter “S” in SAC stand for? Ans: S stands for tin (Sn), A for silver (Ag) and C for copper (Cu).
- How much silver is in SAC305? Ans: 3.0% silver, 0.5% copper and the balance tin (96.5%).
- 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.
- Solder paste is approximately how much by weight metal? Ans: Typically about 90% by weight, or a little less.
- What is not a current common defect in SMT? Ans: (c.) BGA ball matting is not a defect.
- Pad cratering
- BGA ball matting
- Which is closest to a typical stencil thickness? Ans: (c.) 5 mils (0.127 mm).
- 5 microns
- 20 mils
- 5 mils
- 20 microns
- Which is closest to a typical lead spacing for a plastic quad flat pack (PQFP)? Ans (c.) 0.4mm (16 mils).
- Which has finer solder particles, a Type 3 or 4 solder paste? Ans: Type 4.
- What does OSP stand for? Ans: Organic Solder Preservative or Organic Solder Protectant.
- Place an arrow at the eutectic point of the tin-lead phase diagram below. Ans: The blue arrow points to the eutectic point.