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Method for low-cost high-performance optical microlens arrays based on BCB materials and their fabrication processes

IP.com Disclosure Number: IPCOM000010676D
Publication Date: 2003-Jan-08
Document File: 4 page(s) / 122K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for low-cost high-performance optical microlens arrays based on benzocyclobutene (BCB) materials and their fabrication processes. Benefits include improved functionality, improved performance, improved reliability, and improved design flexibility.

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Method for low-cost high-performance optical microlens arrays based on BCB materials and their fabrication processes

Disclosed is a method for low-cost high-performance optical microlens arrays based on benzocyclobutene (BCB) materials and their fabrication processes. Benefits include improved functionality, improved performance, improved reliability, and improved design flexibility.

Background

              Electro-optical interconnections are in high demand due to the high-bandwidth of optical interconnections. However, no conventional solution exists. A requirement exists to incorporate optical interconnections into conventional electrical packages (see Figure 1). Chips communicate with each other through optical signals in addition to electrical signals in the package. One chip contains an array of light sources, such as a vertical cavity surface emitting laser (VCSEL) and drivers. Another chip has an array of photodetectors and amplifiers. An optical signal emitted from a VCSEL array is directed in several ways:

1.   Collimated by a microlens array

2.   Reflected into a waveguide array by a 45-degree mirror array

3.   Transmitted by the waveguides
4.           Reflected by another mirror array
5.           Focused by a focal microlens array
6.           Collected by the photodetectors

      Microlens arrays are required in the electro-optical packages to collimate and focus the optical signal to achieve low optical loss. These packages typically go through solder reflow steps. Therefore, the microlens arrays must be able to withstand the reflow temperature cycles without optical property degradation. Any optical degradation causes additional optical loss and can potentially cause reliability issues.

              Conventional microlens systems are based on thermoplastic polymers such as acrylics and polycarbonates. These polymers have low (<150°C) glass transition temperatures (Tg). They are much lower than solder reflow temperatures, ~210-230°C for eutectic SnPb and 240-250°C for lead-free SnAg. During solder reflow, these microlenses start to flow, which causes shape/dimension change and optical property degradation. As a result, they cannot be used for chip-level and board-level optical interconnects.

General description

      The disclosed method is a low-cost high-performance optical microlens arrays based on benzocyclobutene (BCB) materials and their fabrication processes.

              BCB materials have the same optical properties as acrylics and polycarbonates in the waveguide range from 800 nm to 1600 nm. However, BCB offers numerous advantages including a high Tg, extremely low curing shrinkage, low moisture absorption, low coefficient of thermal expansion (CTE), and stable optical properties. Therefore, BCB microlens systems provide excellent optical performance for chip-level and board-level optical interconnections.

              The BCB microlens arrays can be fabricated using injection molding. This approach can potentially provide microlens...