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SEMI SMT-ELS Standards Suite

SEMI estimates there exist about 80,000 surface mount technology (SMT) and printed circuit board assembly (PCBA) manufacturing lines globally. With that many lines, standards are incredibly important to adding and implementing upgrades and harnessing the power of the data going into and out of the equipment on those lines in the pursuit of efficiency and productivity. Standardized communication system backbones allow individual lines to integrate the latest equipment and software and increase their ROI.

SEMI is developing a suite of standards for assembly line scenarios, like SMT and PCBA. The new SMT Equipment Link Standards (SEMI SMT-ELS) address Horizontal Communication (HC) between different equipment on the line and Vertical Communication (VC) between equipment and higher-tier hosts (for example, a line controller/equipment host or a factory automation host).

StandardsSemiconductor Front-end processing vs. flow-oriented processing


Flow-oriented processes such as SMT are different than typical semiconductor front-end processing, which contributed to the need for the SMT-ELS suite of standards.

  • In the semiconductor front-end space where SECS/GEM was first utilized, the factory host is very involved with equipment control and the process is very job-centric. In addition to configuring and logging information, the host controls equipment execution and has to handle many job and recipe scenarios. For the SMT case, there is more operator interaction on the line and the factory host is currently not really involved with the control aspect and has minimal data collection requirements.
  • In the front-end space, the Automated Material Handling System (AMHS) can take the material anywhere in the factory, including back to a tool where it had been before. For SMT, there is a very fixed flow on where material can go. The SEMI A1 interface provides a way to simultaneously transfer information about the material and material metadata being handed off to the adjacent equipment.
  • Front-end equipment can buffer material for processing using carriers and internal storage locations. With assembly lines, the product comes in, gets processed, and leaves with minimal queuing. The equipment is also very simple. Sometimes, equipment does not even have a PC. Instead, it is controlled by dedicated real-time systems such as programmable logic controllers (PLCs). In these cases, SECS/GEM imposes too much overhead and infrastructure for the functionality required.

Some other considerations:

  • Being job-based, front-end equipment can support more execution permutations. For example:
    • Jobs can be created before or after material arrives at the tool.
    • There are many different carrier validation scenarios to ensure correct material is at the equipment (using either host-based or equipment-based verification).
    • Jobs themselves can support many scenarios with pause, resume, stop, and abort functionality.
  • With SMT lines,
    • There can be up to 10 tracks on the line (although typically there are only one or two and they flow in one direction.)
    • Recipes are pre-downloaded and automatically selected by material data attached to the product when it arrives at the equipment.

The SMT-ELS Standards suite consists of:

This standard defines how to apply SEMI A1/A1.1 to an Equipment Host (provided by Placement Equipment Suppliers) and equipment communication, as well as equipment to equipment communication.

The F-GEM Task Force (under the Japan Automation Technology Technical Committee) is developing a new Standard to support vertical communications using SEMI A1 (and co-existing with SEMI A2) to support a higher-tier host such as the factory automation host that wants to communicate with the line equipment. In the future, this standard could be expanded to support other flow-oriented industries beyond SMT (using only SEMI A1).

Systems and vendors need to work from the same version of the standards to communicate with each other properly. To help ensure compatibility, SEMI is applying Freeze version management to the SMT-ELS Standards suite. Freeze Version 0, announced in October 2019 and specifying the 1019 versions of the SMT-ELS standards, was implemented, and the Automation Technology Technical Committee members are working on updates and prototyping for Freeze Version 1.

For more information about the SMT-ELS standards, visit the SEMI SMT-ELS website or explore the broader SEMI Standards program

SEMI Standards activities are open to all interested parties, but you must be a registered SEMI Standards Program Member to participate in SEMI Standards meetings. SEMI Standards Program Membership is independent of the Corporate, Associate or Affiliate SEMI memberships, but participants are encouraged to join to help support this vital work for the continued growth of the industry.

About the Authors

Terry Asakawa (Principal, VistaIdeal Consulting) has been involved in developing SEMI Standards for over 25 years, focusing on equipment physical interfaces and communication for semiconductor factories. In recent years, he has turned his focus to communication protocol standards for flow-shop manufacturing. Mr. Asakawa currently co-chairs the Japan Automation Technology Committee and leads the F-GEM Task Force.

Albert Fuchigami is Senior Software Developer, at The PEER Group Inc. He is involved in the SEMI Standards development of SMT-ELS so that the effort takes into consideration the differences between front end processing and flow-based assembly lines in collecting data and communicating with factory host systems. He hopes to identify the different use cases and control scenarios, and help users understand the differences, so they know when SECS/GEM and SMT-ELS standards are appropriate.




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