Fibre-coupled PICs: Streamlining The Packaging Experience
Developers are working hard to simplify the assembly of integrated photonic devices so that chips can enter a broad range of markets at more attractive price-points. Ian Oxtoby, optical packaging manager at Optocap, shares the firm's strategy for bringing down the cost and complexity of PIC packaging."‹
Historical PIC development
Since Optocap's formation we have been involved with fibre coupled optical products, supporting multinational companies, SME's & university research groups with their developments and looking at new applications for the technology. We have seen significant changes in the requirements since 2003.
While research organisations and collaborative programs have focused on evolving the technology, the success of PICs in the market rests on heavily on price. Historically, it has been challenging to justify the cost of the customised packages, fibres and alignment processes - even at the prototyping stage.
The expectation is that the implementation cost of new products should be relatively low, because the final product costs of optoelectonic devices in high volume is relatively low. However, the development of highly tuned products in high volume quantities often stems from a significant design cycle that has been optimised over many years. With PIC technology we need to borrow not only from the optoelectronic industry, but also build on experiences from the microelectronics sector in order to match our customer's ambitions.
Optocap understands that new technologies looking to compete with more mature products need to significantly reduce footprint size, power usage or price-point.
The landscape of existing PIC requirements and packaging solutions is not only vast, but hugely variegated in its needs. This has often led to inflexible, application-oriented expensive and tailored solutions in most cases. We at Optocap intend to bring down the complexity and cost of PIC packaging through the introduction of fotonIC - a flexible, robust solution which can cater to the broader needs of industry, while retaining the ability to tailor the platform to more specific applications.
Figure 1. Adaptable approach: 'fotonIC' platform with flexible design adjustments.
Managing expectations & standardisation
In industry, generally it is expected that once the customer has designed a PIC for their application, then it can be packaged to the outlined criterion. This approach often results in reinventing assembly processes already developed as slight variations can have significant implications.
Where customer design sensitivities are more forgiving, a standardised platform needs to address the needs without modification. With a set of design rules, it's important we ensure correlation with our customers and that their designs are focused on meeting key criteria to avoid the more costly issues.
The entry fee for customised packaging is higher and redesigning of the package is costly once a PIC has been designed. However, by using the standard platform, customers can test chips and modify them before committing to this path.
Ensuring that the chip is designed to match the prototyping platform can, not only be cheaper, but critically it can also enable faster package processing. With development time limited and time-to-market so critical, standardisation can only help the diverse PIC package industry.
A standardised approach to package design for pitch, affects the package design cost significantly too. The reason is the utilisation of standard off-the-shelf parts as well as in-house already developed processes. The package cost mainly comes from, for example, developing new optical alignment processes and designing new assembly procedures. Cost increases further with the addition of supporting optical/mechanical components designed specifically for that package only.
By allowing a standardised package assembly to guide a PIC design, the redesigning of package and optical alignment procedures is no longer necessary. This allows for standard FVA Fibre alignment procedures, however, with potentially a compromise on coupling efficiency.
Figure 2. Attributes of standard, customised and custom packages.
Another option that we have chosen to minimise costs is the use of our precision epoxy die attach processes. Often PICs are difficult to metalise and expensive as well. We propose not to use solder die attach unless extreme thermal performance is required. With performance thermoelectric coolers, customers can avoid metallisation on parts along with complexity of metalising the PIC. Optocap's proprietary low stress epoxy die attach processing is a further option.
Figure 3. Technical details
By standardising a packaging platform, we significantly reduce the assembly and design time for the customer. By eliminating the need to redesign the layout, it's possible to make the standardised assembled and functioning package available to the customer in less than third of the normal time.
It can be appreciated that a single platform cannot possibly suit all situations and applications. However, Optocap's "˜fotonIC' platform is targeted to standardise most prototyping requirements. And the flexibility provided by fotonIC platform can contribute towards its acceptance as general standard platform for PIC alignment.
Figure 4. Technical layout for standard/customised PIC alignment.
The fotonIC platform is able to adapt the electrical I/O to customer requirements. If RF connections are required, they can be incorporated in the connection design on PCB. The layout is flexible and can easily be adapted for 3sides electrical contacts.
Another flexibility this platform provides is in adapting to an optical alignment process. In addition to its standard butt-coupled arrangement, several other optical alignment schemes can be adapted - for instance, grating couplers, lensed fibres, angled waveguides etc. These additions can be customised to cater for more specific individual customer needs and can be discussed prior to any assembly assignment.
Figure 5. Summary of the fotonIC Platform
Ian Oxtoby is optical engineering manager at Optocap. He is responsible for the design, verification and qualification of optoelectronic packaged products within the company. With over 20 years in the optical and microelectronic packaging industry, Ian has worked in package development and manufacturing in multiple industries, including telecoms, medical, defence, printing, automotive and aerospace.