SMT Pretest Answers

Folks,

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

Cheers,

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.