VMI Optocouplers and Opto diode PCN

VMI Optocouplers and Opto diode Part Change Notification

PCN release date: 02/10/2023

Description of change

VMI will be changing the configuration of the high-voltage diode that is used in the manufacturing of their optocoupler and opto diode assemblies. VMI's diode assembly consists of stacked silicon terminated by tungsten pins and silver leads. The optocoupler diodes are unique in that the silicon stack is cut in a round (cylindrical) shape. Due to a number of factors, VMI will be changing the geometry of the silicon stack from round to hexagonal. The tungsten pin and silver lead will not change. This hexagonal cut silicon stack change will not affect the fit or form of the of the associated opto assemblies VMI offers. The function of the parts could be affected, depending on the exact application of the part.

Reason for change

Cutting the silicon stack in the round shape requires specialised equipment, the maintenance of which is no longer supported by the manufacturer. Without future support, it is a responsible decision to pivot to a sustainable and familiar process. This proactive approach helps prevent potential equipment breakdowns that could cause delivery or reliability issues with the opto products.

Risk evaluation and functional differences

The majority of diodes produced by VMI use the hexagonal silicon stack configuration already. As a familiar and reliable process, changing these parts from cylindrical cut to hexagonal cut silicon stacks poses no production risks.

Due to the reduced surface area of the silicon stack, and the fact that the optocoupler and opto diode applications rely on the silicon being exposed to light, there will be a reduction in the typical gain percentage for the assemblies. VMI’s evaluation of this change indicates that in their standard optocouplers they can expect a typical gain decrease of approximately 8%. A similar decrease can be expected in applications using VMI’s opto diodes, but without knowing specific application details, it is not possible to predict the exact differences for a customer’s use.

VMI can supply supporting information and documentation upon request. APC are also interested in working with customers to engage in unique testing as it relates to a customer’s specific application.


VMI will be implementing this change to their standard optocoupler and opto diode products on 12/1/2023. For customers who require cylindrical cut silicon stack configured parts for established and qualified applications, we will work with you and put together a plan for testing hexagonal cut parts and end-of-life for the cylindrical cut parts.

For more information about the product affected in this PCN notice, or general enquiries about VMI,
please contact a member of our specialist team.

0330 313 3220 | [email protected]