Using Solder Preforms to Reduce Voiding in BTCs


Let’s see how Patty and the team are doing on their presentation on voiding for Mike Madigan …

Patty was kind of down. Like millions of others, she and Rob watched, in horror, as Jordan Spieth had his meltdown at the 2016 Masters Golf Tournament. Some newscasters considered it the biggest meltdown in golf history, but Patty considered Rory McIlroy’s 2011 and especially Greg Norman’s 1996 meltdowns to be worse. She felt the NY Daily News did the best job of comparing the five worst Masters meltdowns. She agreed that Spieth would surely recover, certainly better than Ken Venturi in his famous collapse in the 1956 Masters. She was surprised that so many newscasters often seemed to not put history in as strong a perspective as it deserved.

As she sat in her office, she was reminded that she needed to finish her part of the presentation that Mike Madigan needed on minimizing voiding. Her topic was, “Using Solder Preforms to Minimize Voiding.” To her, voiding appeared to be the hottest issue in electronics assembly.  Especially voiding under bottom-terminated components, or BTCs. Rob and Pete were coming by in a few minutes to review her progress. Just as she finished, they were at her door.

“Hey, Professor! What’s the scoop on using solder preforms to minimize voiding?” Pete asked, clearly teasing by calling her “Professor.”

They all chuckled a bit and Rob added, “Yes, Professor. Let’s hear it.”

Patty began, “Remember a few years ago the standard approach to using preforms, to minimize voiding under BTCs, was to use a flux-coated solder preform and place it on the thermal pad on the PWB after printing a minimum amount of solder paste?”

“Sure! A great paper was written on it, by some of the folks at Indium Corporation,” Rob said.

Then Pete added, “I gather there is a new approach?”

“Well, think about the motivation to find another technique,” Patty replied.

“A specialized preform needed to be made, it needed flux coating and placing it was a bit of a challenge,” she continued.

“So, what’s the new technique?” Rob asked.

“Well, I chatted with Tim Jensen. Although the original technique is still used, a preferred technique using 0201- or 0402-sized solder preforms has been developed.  The preforms are purposely placed off center so that the BTC is at an angle.  This angle allows the solder paste volatiles to escape.  Since these preforms are a standard size, and not flux-coated, they will typically be less expensive and easier to handle in the assembly process,” Patty elaborated.

“How well do they work?” Pete asked.

“They work quite well. Look at these data,” Patty replied. (see Figure 1).

Figure 1. Preforms of either 0201 or 0402 reduce voiding by up to 50%.  Note that the standard deviation is also tighter by using preforms.

“Looks like the 0402 preforms do a little better than 0201s,” Rob commented.

“Yeah! And using two of them instead of one seems to help a little,” Pete added.

“It’s also striking how the preforms tighten the data up. Look at how much the standard deviation is reduced by using them,” Rob added.

The trio spent the next several hours collating all their PowerPoint slides into one 45-minute presentation. Patty then scheduled a meeting with Mike Madigan to review the entire presentation.

Epilogue: Patty, Rob and Pete reviewed the presentation with Mike Madigan using WebEx.  Mike implemented the recommendations after reviewing them with his critical customers.  By using the best solder paste, making minor modifications to the SMT processes, and using solder preforms where appropriate, ACME was able to reduce voiding to less than 10% in all products and less than 5% in most.


Dr. Ron



Patty and the Professor: Filling the Void


Let’s see what is up with Patty….

Patty sat at her computer, admittedly a little tired. She had just gotten back after a week’s vacation in Colonial Williamsburg with Rob and their two sons. Even though the boys were only five years old, she had insisted that they go to the historical triangle and get the two young lads started on American history. She and Rob had been speaking Mandarin and Spanish at home and the boys were both trilingual, so visiting Williamsburg was among other things Patty had planned to prepare them for a rewarding and productive life.

OK, maybe she was an overachiever for her sons, but she remembered the profound impact that visiting this historic treasure had on her when she was a young girl. During this visit, the young family alternated days at Colonial Williamsburg, Busch Gardens and Water Country USA. They also ate dinner at two of the historic eateries. Of course, at their young age, her boys enjoyed Busch Gardens and Water Country the most.

She had to admit that the trip left her a little shaken. She saw scores of youngsters mesmerized with their smartphones or tablets while standing in line for a ride at Busch Gardens. More troubling was watching teens texting in Colonial Williamsburg while a character interpreter explained the making of a flintlock rifle or the impact of the Royal Marines taking the gunpowder from the Williamsburg magazine, early in the Revolutionary War.

Patty clearly recognized the profound benefit of electronics, after all, it was her career! However, she was troubled by its overuse, replacing personal human interaction and intellectual pursuits and its luring many children away from playing. She was stunned to go to the park where she grew up, a few weeks ago, and finding no children on the swing sets, slides or monkey bars.

More troubling, was a recent chat she had with the Professor. He told her he was convinced that the likelihood of a high school student getting into an elite university was inversely proportional to the number of text messages they send each day. He pointed out that according to Sherry Turkle in her seminal book, Alone Together, the typical US teen sends 200 texts a day. He went on to explain that if a teen sends that many texts a day, how can they have time to be studying Milton or the rise and fall of Rome, learning calculus, or becoming proficient in any topic needed to get into a competitive college or university? To make the point that better students don’t send many texts a day, The Professor even surveyed his statistics class at Ivy University and found that on average the students there sent only about 20 texts a day.

With all of these conflicting thoughts swirling in her mind, she was startled by Pete coming to the door.

“Nous allons à Québec!” Pete shouted. Patty had to shake her head a little bit to get the cobwebs out.

“Hey kiddo, you look a little tired. Too much vacation?” Pete teased.

“Yeah, we didn’t get home ’til 11:30 pm last night. Anyway, what’s up?” Patty responded.

“Well, while you were away, our beloved senior management decided they might want to buy a company in Quebec, near Sherbrooke,” Pete answered.

“Why will we be going to Quebec if we haven’t bought the company yet?” Patty asked.

“The company has 99.5% first-pass yield, but their financials are not that great, especially return on assets,” Pete replied.

“Looks like maybe their uptime or line balancing may be bad,” Patty commented.

“Their throughput would suggest otherwise, for the three lines they have,” Pete said.

“Hmmm, interesting,” Patty murmured.

“Oh, one more thing. They probably need to be using solder preforms on QFNs in some smartphones. They have a voiding warranty issue.” Pete added.

How can a company have outstanding yield and good throughput and still not be profitable? What about solder preforms? Stay tuned to find out.


Dr. Ron