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Publication Date: 09/1/2011
ARCHIVE >  September 2011 Issue >  Special Features: Assembly and Production > 

Solving Small Footprint, Small Space Hermetic Seal Requirements for Semiconductor Fabs
Night vision camera feedthru clearly shows epoxy (blue) filling the aperture.

Even from its earliest days, semiconductor fabrication has challenged and pushed the envelope in the realm of automated, ultra-clean manufacturing. From pressurized work environments to high vacuum deposition chambers, getting power, control and monitoring signals into and out of these non-atmospheric pressure and vacuum environments presents a constant challenge. This is crucial, since the slightest amount of contamination, from ambient air to dust, could scrap a wafer costing $100,000 or more, so this is not an area where failure can be tolerated.

For years, semiconductor fabrication equipment manufacturers have had to work with glass-to-metal (GTM) hermetic seals for wire feedthroughs — often designing around their constraints of size, limited geometry, deflection breakage risk and limited shielding options. Manufacturers have been handed a part that hinders rather than supports the design phase, and only adds to the problems on their plates as they search for a workaround of the constraints inherent in these GTM seals. The problem, however, is only getting worse.
POGO pin feedthru.

As every new manufacturing development comes along, so does an increased need for feedthroughs — for higher power, more controls, and increased monitoring — as well as the feedthrough challenges that come with a GTM seal. Add to this increased signal density, with the attendant need for increased shielding — often relying on twisted pair and twisted shielded pair cabling — and the result is a tough and sometimes impossible scenario to solve with traditional glass-to-metal seals.

Engineered Epoxy Seals
Unlike glass or ceramic seals, today's engineered epoxy seals offer the best of both worlds. The ability to route through tight angles and curves, handle any kind of shielded wire or cable and tightly seal in any shape of feedthrough presents an attractive option. Traditionally, epoxy-based feedthroughs have not been seen as a viable alternative to glass-metal and ceramic-metal alternatives in the semiconductor fab business. But with the space constraints and shielding requirements of today's fab lines, there is a renewed interest in the application of epoxy seals and feedthroughs to solve some of these design challenges.

Traditional benefits of glass-to-metal, such as very high-temperature resilience or ability to hold up to corrosive chemicals, are environments not seen in the semiconductor manufacturing industry. In a -40 to +225°F (-40 to 107°C) temperature environment, such as the ones commonly encountered in semiconductor manufacturing and where an ultra-clean vacuum chamber is top priority, epoxy sealed feedthroughs jump ahead of the GTM in availability, cost and versatility.

The design problem starts with the actual feedthrough bulkhead hole itself. To get the number of conductors required into the chamber, a typical round, threaded hole may not be able to get the job done. The space available in the vacuum chamber may be unique, requiring square, rectangular or triangular feedthroughs — shapes that challenge rigid glass or ceramic seals but are easily accommodated for with ductile, epoxy-based filler. This is a rising trend, as space available for feedthroughs is becoming more restricted, these shapes are requested in an increasing number of projects, and some requests go even further. Unlike glass or ceramic, epoxy feedthroughs can easily be adapted to any shape required, with no compromise in sealing effectiveness.
Multistud power feedthru.

In addition, engineers have probably been in a situation where they would like to test a design during the R&D phase, only to be informed that they had to order far too many GTM seals to meet a "minimum" requirement for manufacturing. Therefore, the fact that customized epoxy seals can be produced in small lots, allowing quick-turn testing during the R&D phase, might be appreciated. Douglas Electrical Components often produces custom lots of 2 or 3 seals. Collaborating with customer's engineers results in a superior solution, as well as advancing the state-of-the-art. Douglas actively encourages customers to prototype. With in-house engineers and domestic production capability, the company can produce samples quickly and efficiently, making sure that the end solution is truly value-added.

Harness Design
An additional area where change can be seen is in the actual connectors and harness design. Ensuring that the feedthrough accommodates the mix of wires, cables and connectors needed for the power, control and monitoring requirements naturally leads to harness solutions. Cabling and harnessing represent another customized component category that greatly benefits from engineering oversight. From high-voltage power studs to shielded-signal feedthroughs, getting the entire hermetic seal package with the right connectors already installed and tested, as opposed to having to deal with solder cups on a glass-metal seal, is a big help on the production line. Again, these solutions are typically provided as fast-turn R&D prototypes, in collaboration with engineers.

Douglas also supplies just-in-time turnkey subassemblies for ion etch tools, ion implant systems and in-line vacuum applications. Parts include multi-layer circuit boards with multiple cable termination on the vacuum side, heated paddle subassemblies and multi-cable vacuum penetrations.

Outside of ultra-high temperature conditions, the company has yet to find an existing glass or ceramic seal application where it hasn't been able to develop a better, faster, less expensive epoxy-based alternative. The company's engineers are constantly pushing the boundaries of epoxy sealing technology, working in conjunction with customers to solve unique feedthrough challenges facing the semiconductor industry.

Contact: Douglas Electrical Components, Inc., 5 Middlebury Blvd., Randolph, NJ 07869 973-627-8230 fax:6-206-6916 E-mail: Web:

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