Insights
As Shiro Sasaki looked at the drawing, his face fell. It showed the electrodes that the customer said they wanted to process on the die-sinking electrical discharge machine (EDM) that they were trialing. Sasaki’s frown deepened as he looked closer.
His mind was full of doubts:
“This might not be possible with our processing machine…”
It was the summer of 2019, and a precision machining company was considering investing in Mitsubishi Electric’s die-sinking EDM. Mitsubishi Electric and its local distributor had been working with this customer for a long time and were determined to make the sale. To help the prospective customer reach a decision, Mitsubishi Electric lent the company a machine for a trial period and provided on-site support, with Shiro Sasaki frequently visiting them as the technical support engineer.
At the time, Sasaki had not been told what the customer planned to use the die-sinking EDM machine for, but as a veteran engineer with over 30 years’ experience in EDMs at Mitsubishi Electric, he was confident that he could deal with whatever the customer needed. With his support, the trial was going well. The machine was able to successfully complete tasks like producing molds for electronic components, and the reviews from the customer were positive.
About two months after the trial began, just as definitive results were gradually starting to emerge, the engineer in charge handed Sasaki some processing electrodes and drawings, saying:
“We want to process this, too.” It was a mold with a finely textured surface.
“It’s an encapsulation mold for semiconductors,” the engineer explained. Semiconductor components are often encapsulated in resin. This is done by pouring liquid resin into a mold, forming the desired shape as it encapsulates the semiconductor component. The matte finish of the mold makes it easier to remove workpieces after molding, as well as reducing light reflection to make it easier to see markings on the surface. The customer wanted to use the die-sinking EDM to produce molds with this surface quality.
EDMs create an arc by bringing an electrode close to the workpiece, melting the workpiece material to the same shape as the electrode. This is an effective way to produce a clean machined surface, as it does not involve applying mechanical force to “tare” away a surface layer in the way that cutting does. This makes EDMs especially useful for applications that require a smooth surface, but for semiconductor encapsulation molds, the surface needs to be rough. What’s more, not just any level of roughness will do—the entire surface must achieve an exact level of roughness required by the customer. Even Sasaki, a veteran EDM engineer, had no experience of this manufacturing process.
When he got back to the Nagoya Works (now Industrial Mechatronics Systems Works), Sasaki went straight to Hiroki Hikosaka and asked him to work on the power supply for the EDM machine. The key to creating a matte surface lay in controlling the arc from the electrode, and Hikosaka had a proven track record in developing EDM power supplies.
Hikosaka and Sasaki had previously worked together for a user in China who needed to produce a particular processing surface using a die-sinking EDM machine. The electronic components made using the mold needed to have a uniform matte finish, and Hikosaka developed a new power supply to meet this requirement. Delivering that project, their partnership succeeded in producing the molds that the customer needed. By teaming up once more, it was hoped Hikosaka and Sasaki could develop a die-sinking EDM machine that could produce the semiconductor encapsulation molds with the required matte surface.
As a test, they tried using the power source that Hikosaka had developed in China to produce the semiconductor encapsulation mold. However, while it significantly improved the processing performance, they could not reproduce the surface finish required by the customer. They found that when processing a fine surface roughness or large areas, the surface processed by the EDM became shiny and consequently did not pass the appearance evaluation.
The test mold was rejected because it did not meet the customer’s surface roughness requirements
Hikosaka continued to improve the power supply, but although the results were getting closer to the surface finish that the customer needed, the next challenge was processing time. To achieve the manufacture of low-cost semiconductor components, they need to be mass produced with high efficiency. However, the customer believed that the improved power supply initially provided would not meet this requirement.
Hikosaka speculated that the reason for the low efficiency was related to the axis controlling the position of the electrode. In an EDM, the distance between the electrode and the workpiece must be precisely controlled, down to the micron level, to produce an electrical arc. But in this case the arc could not be properly coordinated with the movement of the axis, so the arc did not perform as expected. Both experts believed this was the reason for the slow processing time.
Hikosaka and Sasaki realized:
“This can’t be solved with the power supply alone. We need to get a servo engineer involved.”
So, in June 2020, they went to Takayuki Nakagawa, a numerical control (NC) engineer involved in servo development, to ask for help.
Nakagawa had been involved in the research and development of control systems for processing machines, including EDMs, for many years at Mitsubishi Electric’s Advanced Technology R&D Center. Returning after seven years at the Center, Nakagawa was immediately faced with the difficult request from Sasaki and Hikosaka.
(Left) HG type servo motor (Right) MDS-DJ servo amplifier unit
(Top) HG type servo motor (Bottom) MDS-DJ servo amplifier unit
Nakagawa had a servo that was under development for a different application. He wondered if this unit, which enabled precise position control, could meet the challenges of producing the semiconductor encapsulation mold. Realizing why Sasaki and Hikosaka were struggling, Nakagawa began working to improve the servo and solve the problem.
Normally, developing a servo for a processing machine would be a job for the NC department. However, Nakagawa knew that if they asked for a custom servo to be made especially for this EDM, the request would be turned down.
Taking pride in his position at the forefront of Mitsubishi Electric’s development work on control systems for processing machines, Nakagawa devoted himself to improving the servo. There were times when he would upgrade the same servo as many as five times a day.
As Hikosaka worked on improving the power supply and Nakagawa worked on improving the axis control, there were signs of progress. However, the machining results were still nowhere near delivering the surface finish that the customer required. In addition new issues kept emerging, causing the situation to oscillate back and forth between progress and deadlock.
After one year of trial-and-error progress, a decision had to be made. Normally when an EDM machine is lent out for evaluation, the duration is for around six to twelve months, by which time the trial process needs to be completed. Sasaki decided to call the sales department and ask for an extension of the trial period, but Sasaki himself had a feeling that it would not be enough to solve this problem.
In April 2021, after the trial had gone on for one year and nine months, the customer’s senior management contacted the sales representatives from Mitsubishi Electric and the distributor and said:
“We are sorry to say this after you have gone to so much trouble, but…”
The customer had chosen to end the trial, as they felt that the prospect of a solution was not in sight.
After this meeting, Sasaki’s phone rang; it was the sales team. When Sasaki and the others heard about the rejection, they had nothing to say in reply, but they felt they had in some way failed the customer.
They had run out of time and the EDM machine was returned to the Nagoya Works.
With the growing spread of 5G technology and battery electric vehicles, there is increasing demand for semiconductors.
To address this need, Mitsubishi Electric has developed its semiconductor package option, which supports the production of semiconductor encapsulation molds, a vital part of the semiconductor manufacturing process.
