Indium Blog

Use an SMT Pre-Test Before Presenting a Soldering Workshop

  • Soldering

  • Folks,

    Let’s see how Patty is doing, it’s been a very, very long time...

    Even though Patty and her husband Rob both worked at Ivy University, they seldom drove in together. It was just too difficult to organize their schedules so that it would work out. So, as Patty was driving in to Ivy U, she was listening to the last chapter of Ron Chernow’s biography of U. S. Grant. Her timing was excellent, since she, Rob, Pete, and the Professor were having their monthly book club meeting. Rob, Pete, and the Professor were always recommending books about World War II or the Civil War. Because of this trait, she groaned every time it was the three “boys” turn to suggest the next book. But, she had to admit that she always enjoyed the books much more than she thought she would. She especially liked a book Rob discovered, called A Simple Solder. Patty found this true story, about a young boy in the German army in World War II and how he survived to tell the tale, fascinating. She would never tell Rob, but she read it three times.

    When it was Patty’s turn she made sure to avoid those military topics. Recently, she proposed another one of Chernow’s biographies on John D. Rockefeller. She also suggested  iGen: Why Today’s Super-Connected Kids Are Growing Up Less Rebellious, More Tolerant, Less Happy--and Completely Unprepared for Adulthood--and What That Means for the Rest of Us by Jean M. Twenge. This book convinced her and Rob to dramatically limit “screen time” for their 9 year old twin boys.

    As she approached her parking spot, the audio book on Grant finished. She was a bit sad, as she had enjoyed this book as much as any. Patty had the impression, from her high school history classes, that Grant led the Union to victory over Robert E. Lee only because he had superior forces, weapons, and supplies. Chernow’s book clearly dispelled that notion. Grant was a great general. In addition, he was an effective and honorable president, if a little too naïve and trusting to avoid numerous scandals among his subordinates.

    In a few moments, they met in The Professor’s large office. After they finished their book club chat about Grant’s biography. Patty had a favor to ask.

    “Mike Madigan asked me to give a 3 day workshop on ‘SMT 101’ at one of ACME’s recently acquired facilities. He said he felt the technicians and engineers weren’t very knowledgeable. I’m having trouble deciding at what level to aim the workshop,” Patty began.

    “You mean like for beginners, intermediate, or expert?” Pete asked.

    “Yes,” Patty responded.

    “Well, you should develop it in a logical sense, starting with what soldering is, discuss flux and solder paste, then stencil printing, component placement, reflow, test, etc,” Rob added.

    “I agree with Rob’s outline, but you need to find out the current knowledge level of the students,” The Professor suggested.

    “I once gave an 8 hour seminar on ‘SMT Defect Modes and How to Fix Them.’ The workshop was advertised as for SMT engineers and technicians with intermediate experience. At the end of the workshop a person raised his hand and asked an unsettling question,” The Professor continued.

    “And the question was?” Pete teased.

    “Professor, you have used the word ‘SAC’ many times, what does ‘SAC’ stand for?” The Professor responded.

    In unison, Patty, Rob and Pete groaned.

    “That’s my concern! At which level do I aim the workshop? If I shoot too low, it might insult people. If I shoot to high it might go over their heads,” Patty responded.

     “OK! So, how do I structure the workshop, not knowing the skill level of the students?” Patty asked a little frustrated.

    “How about a pre-test?” The Professor suggested.

    “OK! But how many questions?” Rob asked.

    “It needs to be short, yet comprehensive,” The Professor suggested.

    “Seems like a contradiction,” Pete grumbled.

    “I think The Professor is right. Look at it this way, let’s say you want to assess if your 14 year old nephew knows much about The Civil War. Ask him three or at most five questions and you can determine if he does,” Patty suggested.

    “How about some examples?” Pete asked a bit dubious.

    “I’m getting it. How about when was the war fought, who was Robert E. Lee, what is the significance of Appomattox Court House?” Rob chimed in.

    “OK, I see you point. If you know two or all three, you probably know a lot, one or less and you don’t know much,” Pete responded.

    Patty then suggested, “OK let’s develop a list of ten SMT Pre-Test questions.”

    After about 20 minutes of back and forth, our team of four converged on these ten questions.


    SMT Pre-Test.

    1. What does the letter “S” in SAC stand for?
    2. How much silver is in SAC305?
    3. PWBs are coming off of the final component placement machine at a rate of one every 20 seconds. The PWBs are 20 cm long and should be placed with at least 4 cm of space between them. What must the reflow oven belt speed be to accommodate this cycle time?
    4. The starting temperature is 25°C. It needs to be 145°C in one minute. What heating rate is needed, in °C/s, to achieve this temperature?
    5. About how much does silver cost per troy oz.? (+/- 30%)
    6. Which is a closest to typical stencil thickness?
      • 5 microns
      • 20 mils
      • 5 mils
      • 20 microns
    7. Which is closest to a typical lead spacing for a plastic quad flat pack (PQFP?)
      • 0.1mm
      • 0.1 mil
      • 0.4mm
      • 0.4 mils
    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.

    Would you like to try the pre-test? The answers have to be what you know without looking anything up. Send me your answers at The first person to get 100% will get an item of memorabilia signed by Patty, Rob, Pete, and The Professor.

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