Update from SEMI

By Paula Doe, SEMI

SEMI provides guide to evaluating hermeticity of MEMS packages

SEMI aims to promote development of MEMS markets with its new guide to evaluating the hermeticity of MEMS packages.

“This hermeticity guide is the first to address MEMS packaging,” noted Ron Foster of axept, LLC, who chaired the industry committee that drafted the new standard.  “We anticipate further efforts to standardize the methods used to evaluate MEMS packaging and the types of packages used in an effort to make MEMS more economical for manufacturers, users and consumers.”

The latest in SEMI’s series of MEMS standards, MS8— Guide to Evaluating Hermeticity of MEMS Packages, is available to users on-line immediately and on CD in early spring. 

The guide offers a comprehensive summary of MEMS hermeticity issues as the first step towards developing a test method standard.  Industry representatives on the MEMS technical committee worked out standardization on terminology, categories of use, methods for sealing, seal integrity evaluation and the detection and measurement of hermetic leakage, especially for small volume packages. The document will be revised and expanded upon as more data and MEMS-specific information becomes available, eventually leading to publication of a specification or test method standard.

The committee is now looking more closely at the permeability of sealing materials, which has a direct effect in determining if a seal is “accepted” or “rejected.”  Once the seal is inspected for integrity, and the bond quality is good at both interfaces, with no direct leak paths between the external and internal environments, permeation of gases through the seal becomes a key determinant of device life expectancy. And the permeability of the seal material determines how thick the seal must be for a given lifetime. Although a primary concern for hermeticity, there is little published data on permeability of seal materials used for MEMS. 

Another issue of concern is the validity of the current test methods for leak testing and residual gas analysis.  These test methods were developed for packages with larger cavity volumes and have proven to be neither applicable nor reliable for smaller volume packages, of <0.02 cc or so. The published guide provides objective discussion and evaluation of both standard and recently introduced test methods.

Ideally, as the production volume of commercially available hermetic-packaged MEMS increases, a method will emerge that supports high-throughput non-destructive hermetic quality control.  Perhaps one of the methods discussed in the MS8 guide will become a self-contained standard, but further investigation and input from the MEMS industry is required to develop consensus.

SEMI’s MEMS group has published seven other standards related to MEMS and is working on developing more as needed by the industry. The utility of SEMI standards depends on the insight of people involved with MEMS on many levels. 

About the SEMI MEMS Technical Committee: The MEMS Technical Committee formed in 2003 to develop standards for MEMS devices not handled by existing technical committees.  Current topics include wafer bonding alignment targets; step-height measurements of thin, reflecting films using an optical interferometer; and ultra high purity microscale fluidic systems for scalable process environments.  The North American MEMS committee will next meet July 13 at SEMICON West in San Francisco.

For more information on MEMS committee activities, please contact Susan Turner at sturner@semi.org in North America, or Saviour Alfino at salfino@semi.org in Europe.

Heads up on MEMS events at SEMICON West

Here’s what’s planned so far for SEMICON West this year on MEMS, and related topics brought up at METRIC of particular interest to MIG members.