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Using Solder Preforms to Reduce Voiding in BTCs

Category:
  • Avoid the Void
  • Folks,

    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?” See figure 1.

     Figure 1.  A specially designed flux-coated solder preform placed in solder paste printed on the PWB pad can significantly reduce solder voids.

    “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 of Indium Corporation.  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. (See figure 2.) 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.

     Figure 2. Standard 0210- or 0402-sized solder preforms angle the BTC so that solder paste volatiles escape.

    “How well do they work?” Pete asked.

    “They work quite well. Look at these data,” Patty replied. (see figure 3)

    Figure 3. 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 of 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.

     Cheers,

    Dr. Ron

    If any reader is interested in more detailed information on any of the solder pastes, preforms or processes, send me a note at rlasky@indium.com and I will send the information to you.