Molded Caps & Lenses for Transistor Outline Packages

Product Description

Molded TO packages
Optical sensors are highly sensitive to a number of environmental conditions, and are particularly vulnerable to damage caused by humidity and certain chemicals. They can be protected by welding protective transistor outline caps to the transistor outline (TO) headers in which they are packaged. However, at the same time, it is vital to ensure that the caps meet a range of optical requirements to ensure the consistent transmission of optical signals.

SCHOTT molded TO caps, also referred to as "direct seal caps" are sealed hermetically by fusing the glass directly to the metal frame without the use of any other interface materials. This is achieved by reheating cooled glass and then fusing it with the metal. The fusion process must be designed in such a way to ensure that the glass cools down without the formation of bubbles and inclusions and obtains the correct optical properties, which is often subject to very low tolerance limits.

Fusion molded TO caps can also be manufactured with windows and convex (plano and biconvex) lenses, and with various kinds of filters for special applications. Windows and lenses can be supplied in a range of designs and according to customer specifications.


We carry a full assortment of standard windows and lenses. The molded caps provide a high level of safety and reliably retain their optical properties over the years.

Since the glass used in these applications only obtains its optical properties after fusion, these caps can be manufactured from untreated industrial glasses.


Molded TO caps and lenses are particularly suitable for use with integrating sensors, for example for light intensity measurements (motion sensors, infrared temperature measurement, etc…), and can be used for encapsulating photodiodes for use as receivers in data communication.

Technical Details


The caps are generally manufactured from Kovar® (ASTM-F15) and types of glasses particularly suited for use in UV light. The finished product can be electroplated to customer specifications.

Please refer to our glass-to-metal seal technology page for more information about this hermetic sealing process.

Features / Specifications

The caps can also be supplied with various optical coatings, including:
  • Anti-reflective coatings
  • Beam splitters
  • Filters
Please refer to our Optical Properties section for more information on coatings.

Forms of Supply and Product Packaging

All molded TO packages can be supplied in loose form or packaged individually and supplied on trays.


All our production facilities are ISO 9001 certified. All our molded TO caps and lenses comply with the International Telcordia Specifications and all products are ROHS compatible.
Exhibitions & Events
Exhibition CIOE - China International Optoelectronic Exposition, Shenzhen, China, 09-01 to 09-03-2021
Exhibition Gastech, Singapore, Singapore, 09-13 to 09-16-2021
Electronic Packaging
SCHOTT North America, Inc.

15 Wells Street
Southbridge, MA 01550
E-Mail to SCHOTT+1 (508) 765-7450
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