Indium Blog

SMT Workshop Pre-Test

  • Soldering

  • Folks,

    Six months ago…….

    Patty had just finished an all day workshop on “Common Defects in SMT Assembly and How to Minimize Them." The workshop seemed to go really well, and many of the 35 or so attendees thanked her for a great learning experience.

    After most of the people filed out of the room, two approached her as she was disconnecting and packing her laptop.

    “Dr. Coleman, that was a great workshop. But, I do have one question. You used a term all day that I wasn’t familiar with, ‘SAC’,” a 35 year old process engineer commented to her.

    While saying this, he presented his business card that referred to him as a “Senior Process Engineer.”

    Patty was trying to recover from this shock, when the second similar looking fellow asked, “And what are ‘OSP’ and ‘eutectic’.”

    After explaining these three terms and exchanging a few pleasantries, the two senior process engineers walked out of the room and bade Patty farewell. As the room became empty, Patty settled into a chair.

    “How can this be?” she thought. She was stunned that people with enough experience to be called “senior process engineers” would not know these terms.

    Today 6AM……

    Patty was jogging back to her house in Woodstock, VT when she spied a beautiful red fox. Neighbors had reported seeing the fox numerous times. People believed that the fox was nesting. In addition, a black bear had been sighted by everyone in her family over the last few weeks. Add all of this to the family of deer and the rafter of turkeys in her neighborhood and it was quite an experience for Patty, Rob, and their sons.

    The fox, however, created a new problem. Patty and Rob had bought their twin sons a Yorkshire puppy, Ellie, about a year ago. At 6 pounds she could be dinner for the fox, so, unfortunately, they could no longer let Ellie out by herself.

    Figure 1. Ellie the Yorkie after a big day. Sadly she has to be watched when she goes outside of Patty's house, due to the local predators.

    By 7:30AM Patty was in her office. She was giving a workshop in two weeks at a local chapter meeting in Boston and decided to create a pre-test to give to the attendees so that she could assess their current knowledge. Patty planned on having the students grade each other’s exams and on working the exam in as a leaning experience at the start of the workshop. By assessing the results of the pre-test, she wanted to make sure she didn’t use acronyms they don’t understand, and to also explain topics that the students might not be familiar with. As she was working on the questions for the pre-test, Pete walked in.

    “Hey, Professor C, how goes it?” Pete asked.

    “I’m preparing a pre-test for the workshop I’m giving in a few weeks,” Patty replied nonchalantly.

    “I remember you talking about doing it a month or so ago. Seems like a good idea to me,” Pete responded.

    “I'm ,glad you approve," Patty said wryly. "I just finished it. Do you want to take a look at it?” she continued.

    Patty printed out a few copies and handed one to Pete. They both looked at it for a few minutes, in silence.

    Finally, Pete commented sheepishly, “Aaa, Patty your joking, right?”

    “Why do you say that?” Patty asked, a little annoyed.

    “It’s just too easy. Everyone will get 100% and you won’t get any information,” Pete opined.

    Patty then reminded Pete of her experience 6 months ago.

    “OK. Maybe you have a point. But, I still think it’s too easy,” Pete concluded.

    “I’ll tell you what. How about a bet? If the average pre-test grade is above 70%, Rob and I will take you and your new crush, Mary, out to Simon Pearce. If it is 70% or less, you treat us,” Patty teased.

    “It’s a bet,” replied Pete quickly.

    The Pretest:

    1. What does the letter “S” in SAC stand for?
    2. How much silver is in SAC305?
    3. What is the approximate melting point for SAC305 solder (+/- 4oC)?
    4. Solder paste is approximately how much (by weight) metal (+/- 5%)?
    5. What is not a current common defect in SMT?
      1. Head-in-pillow
      2. Pad cratering
      3. BGA Ball Matting
      4. Graping
    6. Which is a closest to typical stencil thickness?
      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)?
      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?
    9. What does OSP stand for?
    10. Place an arrow at the eutectic point of the tin-lead phase diagram below.

    Epilogue (two days after the workshop)

    Patty arrived at Ivy U and couldn’t wait to see Pete. She went to his office but he wasn’t there. Finally, she found him in the machine shop helping four students with a project that required some additive manufacturing.

    “Hey, Pete! When are you and Mary going to treat us to our dinner?” Patty teased.

    “Don’t tell me the average was less than 70%,” Pete grumbled.

    “Forty-three point zero eight to be exact,” Patty punctuated.

    Figure 2. The Pretest Scores

    “Yikes!” Pete exclaimed, rubbing the back of his neck. “I guess you were right.”

    “It really helped me to take things slowly and explain all the terms. I think I helped the students much more than usual,” Patty explained.

    “Rob and I both agreed, we are ordering the most expensive meal that Simon Pearce has,” Patty joked.

    At that Pete let out a deep groan.


    Dr. Ron note: All of the events in this post are true. How would you do on the pretest?