Estimated reading time: 4 minutes

Maggie Benson's Journey: Teaching About Solder Paste

Editor’s note: Indium Corporation’s Ron Lasky continues this series of columns about Maggie Benson, a fictional character, to demonstrate continuous improvement and education in SMT assembly.

Maggie Benson and her fiancé John were relaxing at the grill at the Woodstock Country Club with their mentor, Ivy University’s Professor Patty Coleman, and her husband Rob. As usual, Maggie and John were bested at golf by Patty and Rob.

“Maggie, John, thanks for giving us a tour of the vastly improved Ivy-Benson Electronics yesterday,” Patty began. “The change seems miraculous.”

“I agree,” Rob chimed in. “The improved facilities and the change in the workers are impressive. Especially the workers—they seemed so enthusiastic and committed.”

“Well, the improvement in the facilities is something easy to understand,” Patty said. “You invested a lot of money and sweat equity to bring the facilities up to date. But what caused the change in the workers?”

“We couldn’t understand it either,” John answered. “Our training program and paying for college courses are partly responsible, but we were missing something.”

“Then it became obvious that part of the magic was one young couple,” Maggie added.

Maggie and John then proceeded to tell the story of Andy and Sue. They explained that Andy and Sue’s newfound passion for learning and self-improvement was contagious.

“What was really interesting is that both of them were constantly asking questions of their co-workers to understand all the aspects of electronic assembly,” Maggie elaborated. “This trait became contagious, as the other workers wanted to learn more, too.”

“One of the chaps, who was a little rough around the edges and a sloppy dresser, came into work one day sporting a complete makeover. He was well groomed and dressed in smart business casual attire,” John said. “I complimented him, and he told me that seeing Andy so ‘with it and enthusiastic’ encouraged him to make a change.”

Meanwhile, at their favorite pizza shop, Sue and Andy were working on their homework and preparing to give their second class at Ivy-Benson.

“How is ‘Miss Can’t Speak in Front of a Group’ doing?” Andy teased.

“Thanks for helping me in the first class,” Sue said. “Toward the end, I actually felt comfortable speaking to the group. It helped that you lectured, and I just answered questions.”

“Well, at the end you were speaking more than I was,” he responded. “I think I could explain the derivation of the area ratio formulas, but you did it much better than I could.”

“This has been a big breakthrough for me,” Sue said, with a little shakiness in her voice.

“Anyway, are you ready for tonight’s math class?” Sue asked.

“Yikes, trigonometry,” he said, jokingly. “Though, I have gotten sine, cosine, and tangent memorized with the mnemonic: Oscar had a heap of apples¹.”

Off they went to their math class and, after class, ended up in their favorite ice cream parlor to discuss the next SMT lesson they were teaching.

“In three days we teach the very basics of how solder paste is made and how it functions,” Sue began, with Andy responding, “I found it fascinating.”

“I think it’s neat that the solder powder can be made by taking liquid solder and splashing it on a fan blade,” Sue commented.

“Yeah, then they put the powder through screens to get the desired particle size distribution,” he added (Figure 1).

“What I never appreciated was that solder paste is a multifaceted material. What everyone refers to as flux is really a complex mixture of materials that not only enables effective soldering but must have the right viscosity for printing and tack to hold the components,” she said.

“Another interesting property that a solder paste must have is good response-to-pause²,” Andy said.

“That’s one thing I haven’t heard of,” she replied.

“Well, when you stop the line and the stencil printer is not printing, some solder pastes stiffen and the first print after starting up is not useable. So, that board has to be wiped clean and reprinted. Chuck Tower said that Ivy-Benson had used a paste that had this problem, and it caused a lot of downtime. The paste was very cheap but ended up causing the company to lose money because of the downtime. We switched to a paste that did not have this issue and even though it was a little more expensive, the new paste saved us thousands of dollars,” Andy said.

“Another thing that I learned was that the fluxing action of solder paste goes beyond removing oxides from the PWB pads,” Sue said. “The flux must also be an oxygen barrier to protect the solder particles during reflow.” She then showed a PowerPoint slide that depicted all the functions of a solder paste flux (Figure 2).

“Wow, the flux in the solder paste is really quite complex—it has to perform so many functions,” Andy said. “It is easy to see why Chuck calls it a highly-engineered material.”

They continued to prepare their slides for the upcoming workshop. As they headed out for a brief moonlit stroll, Andy commented, “The next class is on component placement and line balancing. For line balancing, I’m going to have to lean on you heavily for this one.”

Will Andy be able to teach line balancing without heavily leaning on Sue? Stay tuned to find out.

References

1. Trigonometry mnemonics, Wikipedia.com.
2. “Response to Pause: A Critical Solder Paste Parameter,” by Ronald C. Lasky, Indium Corporation.

This column originally appeared in the August 2022 issue of SMT007 Magazine.