The development of both Opto “photonic” and RF technology into silicon based chip solutions is creating a demand for smaller, more cost effective solutions to house the devices. The use of Thermoplastic mold compounds with pre-plated leadframes is one of the most viable solutions for volume take-up at low cost. HHEM have developed novel mold design assembly and process techniques to produce such package solutions for these new markets. The issues involved and the solutions achieved are reviewed, including a novel patented process, which provides isolation between interconnect levels in more than one plane. New approaches to design of application specific packages are used to show how matching function to environment can provide novel housing solutions. The capability to provide higher performance characteristics such as heat transfer and hermeticity in
’plastic’ packaging remains the challenge for both RF and optical devices. Some of the work ongoing and results obtained with commercially available and proprietary process material is reviewed.
INTRODUCTION
The growth of Opto “photonic” technology and its development into silicon based chip solutions has created a new demand for Chip packaging technology to provide smaller, more cost effective solutions to house the devices.
In fact many photonic applications would be improved if the housing could be specifically designed to suit both the interconnection between the chip and the control circuitry, and the physical aspects of the location of the optical sources in its overall application.
Additionally the rapid growth of wireless products has increased the demand for higher power, lower cost RF components. Devices previously designed for military and aerospace applications now need to be produced in a manner and at a cost more suited to consumer market products.
Packaging of these Opto and RF components is one of the most costly parts of the whole manufacturing process. Package costs in excess of 50% of the overall device cost are not unusual, whereas in traditional IC packaging a cost of less than 5% is more the requirement.
Handy&Harman Electronics Materials Group
(HHEM) in the USA have for many years provided a capability to design and manufacture innovative leadframe and
Thermoplastic molded parts for medical and electronic applications. However the
Semiconductor “chip” industry, until recently, has not been in favour of injection molded or insert molded packaging due to an outdated view that the technology involved is incapable of meeting the quality needs for performance and reliability.
It has been the advent of chip based sensor products, especially “opto” parts that has prompted a change, in terms of needs for cavity packaging. This has in turn created needs to use latest technologies and materials to reinvent the thermoplastic package capability.
HHEM have become one of the new pioneers

in developing these technologies to suit RF and
Photonic packaging applications.
CAVITY PACKAGES OVERVIEW
Due to the nature of the chips being used in these specialised applications, packaging them has generally required the use of a cavity style of carrier. There are a number of options for cavity packaging as shown in table 1. These range from machined metal cavity through formed “cans” and Ceramic types to leadframe and plastic options. As shown they have relative cost and assembly issues which need to be considered for volume applications.
Table 1
Cavity package options
There are a large number of suppliers and manufacturers offering capability in all these types but only a few companies, mainly
Japanese Ceramic package suppliers, can offer products for volume manufacturing. In plastic overmold assembly some new, high cost mold designs and processes are being developed for some of the volume applications, but these are only feasible if the chips are not affected by the heat and pressure stresses exerted in the molding processes.
So these new markets have at last seen the need to change to match the demand for cost effective packages for silicon based RF chips,
Opto chips, MEMS and Sensors that need specialist chip “packaging” with a cavity. The relatively lower tooling costs coupled with capability to match existing volume assembly equipment have been the key factors in reawakening the market to the capability of injection molding technology. In addition other benefits such as colour, shape, surface finish and dimensional stability are offering advantages previously not considered.
REQUIREMENTS FOR RF AND
PHOTONICS PACKAGING
Because of the lack of “standards” in the emerging markets, RF and Opto companies have generally developed their own application specific or custom cavity packages.
In Photonic applications these packages have generally been suitable for prototype and low volume requirements but these solutions are costly and create a wide range of problems when moving up to volume assembly.
An example of this issue is related to the manufacture of products such as Fibre Optic transceiver units and VCSEL devices. The assembly processes are based upon the need to have trained operators to individually ‘hand’ align and set component positions. Assembly lines for such devices resemble the IC industry back 30 years, when wire bonding was manual or at most only semi –automatic. In this respect, device manufacturers have requested equipment manufacturers and materials suppliers to find ways of using available automated lines and adapt them to meet the high accuracy needs of opto components(1).
Such calls are now being responded to by some of the major suppliers(2) who have recently introduced a range of ceramic cavity package parts based upon a leadframe strip (figure 1) rather than being individual units. The move to leadframe technology clearly demonstrates that this approach is the realistic factor in meeting the needs of high volume assembly.
Figure 1 – Kyocera Ceramic packages on lead frames
On the other hand, the rapid growth of RF transistors, MMIC’s and GaAs devices necessary for the wireless and mobile phone applications, has meant that the few ‘volume’ package suppliers have now generated “de-

facto” standard package parts in order to help reduce costs. The cost trade off here is that the chip designers are having size or layout constraints that are either increasing design costs or reducing functionality.
Because of the needs of these devices to handle
RF power, heat generation is the major concern followed by issues related to the electrical effects of the package parasitics reducing speeds and limiting frequency functionality of the devices. These ‘standard’ cavity packages for RF are developed around gold plated heat sink base plates and therefore are individual packages that do not lend themselves to automation in assembly. So as volumes increase cost for procurement and assembly become increasingly significant. The trade off is that there are multiple sources of parts but until recently none have really addressed the requirements to automate assembly.
RF packaging brief
The key factors for RF device packaging depend upon the applications and the operating frequency requirement. The RF frequency range is from above 400Mhz to the low microwave frequencies of up to 10GHz (4).
Most of the new volume wireless applications are in the 2 GHz – 5 GHz range but eventually these will be going on up to 40Ghz and beyond.
For these wireless frequencies the package constraints are:
•
Thermal Management
•
Parasitics (L R C)
•
Cost
These in turn dominate both package design and the assembly process in terms of die attach capability for thermal and electrical contact through the package base. Wirebond needs affect the lead finish (gold is the standard) and package lead size affects the frequency due to parasitic inductance. Interestingly, package sealing is not an issue, as non-hermetic environments do not now affect many devices.
Volume manufacturing of many RF power products is, and will remain, in standard IC power packaging now that thermally efficient packages are prevalent. But the stresses generated in thermo-set transfer mold processes can be damaging to a number of technologies in RF devices. In particular, RF power transistors require metal based cavity packages to meet the thermal and electrical conductivity needs. Further as higher frequency demands dominate, the packages must have bigger interconnect leads to reduce parasitic effects.
For these reasons there has been a significant growth in the Ceramic RF and Microwave package demand but this has so far failed to be cost effective. Leadframe technology is now being developed (2) for low power devices in order to get cost effective solutions both in material and assembly costs. Consideration of molded plastic cavities is the next challenge.
Photonics Packaging brief
The developing range of photonic devices is integrating more functions in a rapidly shrinking component size. The more the integration the more complex the package becomes which inherently adds cost.
Current and emerging products also have the same basic, unique needs for packaging. A review of the assembly issues involved (3) has identified the key factors (which also apply equally to RF packaging) for consideration in choosing the package, namely:
•
Electrical conductivity
•
Operating temperature range
•
Expansion coefficient
•
Surface finish
•
Ease of installation
•
Cost
Associated with these the major challenges to packaging and assembly of Photonic devices
(3) are:
•
Alignment of components to within
0.5 micron
•
Substrate selection
•
Thermal management
•
Sealing
In reality, these issues are no longer exclusive to photonics as they have now become predominant in standard IC chip packaging.
The industry needs to package camera chips and other opto sensors with accurate alignment, it requires wirebond placement accuracies less than 5 micron and it needs to manage the heat increases from shrinking chip geometries.

Much of the equipment available on the market can therefore now be used in the assembly of photonics, but materials and packages used will have to adopt standard semiconductor assembly criteria to suit to these machines.
Leadframes are a natural choice, allowing strip-to-strip assembly with standard magazine storage and control. They also provide thermal and electrical conductivity. The cavities, as seen earlier in metal and ceramic can be applied to frames, but these are not that cost effective. The use of insert molded or premolded thermoplastic housings are being considered as a cost effective choice. Wide ranges of mold compounds and very accurate mold capability can now meet the demands of this new industry.
Figure 2 – Profiling of cavity features. (courtesy of Kyocera)
Additionally, the cavity package design can be customised both internally and externally to match the application at relatively low cost. As shown in figure 2, the internal design of this ceramic cavity can be adapted to accommodate a fibre connector location or fibre ‘pigtail’, which provides high accuracy alignment as well as reduced interconnection costs. In this application, plastic molded cavities can be more dimensionally accurate with tighter tolerances than ceramic.
MANUFACTURING TECHNIQUES
Advancement of Leadframe technology, development of injection mold technology, introduction of new materials and novel design ideas are the tools that have been developed by the package manufacturers to ensure that today’s pre-molded leadframe cavity packages can match the demands of these new and emerging markets for RF and photonics devices.
Cavity package issues raised by the
Semiconductor packaging Industry in its early years, when Thermo-set compounds became the viable solution to encapsulate chips, still exist as a mindset in many Chip companies.
These relate to package strength, sealing, hermeticity, quality, dimensional accuracy and cost. However Chip package manufacturers rarely use cavity packages since the demise of
Metal Can, CERDIP and Ceramic Sidebraze assembly capabilities.
Recent growth in Sensor technologies and
Opto components (LEDs etc) has seen a resurgence in cavity packaging assembly needs. Pre-molded frame technology has been the key to the successful growth of these industries and manufacturing techniques have also been developed to support these industries.
Likewise, engineers at HHEM have developed novel mold design, assembly and process techniques to suit the demands of these new industries and to enable use of new materials now available.
Mold machine developments
Injection mold technology is widely used in a number of industries where precision parts are required. The medical industry has for many years used such technologies and HHEM’s background in this industry has enabled the development of a high performance molding capability.
Figure 3 – Three plate Mold system
The key development has been that of a pioneer 3 plate mold system enabling the insert mold capability of leadframes in a vertical plane as in figure 3. This mold system ensures that the frames are accurately aligned with the

mold features then firmly clamped in the molds, enabling good fill on mold shots and preventing bleed. Additional development of
“dry” mold technologies has resulted in an accurate, clean component with extremely fine surface features. To keep costs down, and provide high volume capability mold machines have been adapted to allow reel to reel leadframe feed.
The molds themselves are built upon standardised mold bases incorporating 4,16 or
32 cavities. This is done to keep tooling costs to an absolute minimum and provide fast turn round of new designs. Most prototype and pre production can be done on a single cavity, which allows very small size features and rapid adaptive design changes before production tooling investment is needed. Accuracies of tool placement and cavity features can be under
5 micron.
Mold Compound issues
As one would expect, the development of new thermoplastic mold compounds has increased greatly in the last few years, as products in a broad ranging number of applications from toys to Aeroplanes require different material performances. A list of compounds typically used in electronic components is shown in table 2. The choice of mold compound can depend on many factors, including colour, but the current prime option for high performance cavities is the black Xydar product. This has a
CTE that closely matches the applications and high melt point to match assembly needs. On an aside, thermoplastic compounds are recyclable, an important feature for the industry in coming years.
The main driver in the electronics cavity package market has been for higher and higher melting point materials. These need to withstand the assembly processes which continue to push the temperature and stress of components, such as solder reflow for lead(Pb) free electronics which is now around 300°C.
HHEM have pretty much standardised upon
LCP, a material widely used in the connector industry, as it has a good performance, high temperature withstand and can provide fine resolution geometry.
Table 2
Mold Compound options
A new compound, known as “conduit” has now been made available to HHEM for use in high thermal stress applications. This has been tested up to 500°C and is likely to be used in
RF package units which use eutectic die attach reflow processes. Results of tests so far show that it meets the same stringent environment as
High temperature ceramic materials, bonded to metals.
Multi - Leadframe capability
Leadframe design is also a key part of the package development cycle. Use of HHEM capabilities to stamp and pre- plate frames before molding for volume applications means that all packages developed can benefit from
Lead (Pb) Free finishes. Packages are generally tooled for multi-up parts – depending upon mold tool designs – that ensure lower cost in terms of tooling investment and unit prices. Multi-up frame devices are pretty much commonplace for standard Semiconductor assembly equipment.
To utilise the capabilities of the cavity package for Chip devices that require thermal management, HHEM have developed a novel, patented process adaption that will allow the use of a second leadframe to provide the cavity package with a metal base that is isolated from the i/o configured leadframe. In fact the

process developed can simultaneously mold up to 3 frames at the same time allowing development of 3 dimensional package options. The frames can be maintained at a minimum distance apart of 0.4mm and frames can be of varying thickness up to 2mm. This isolation between interconnect levels in more than one plane offers a new packaging technique opening up more opportunities for new types of optical and bio-metric sensors as well as other devices such as power hungry, radio frequency chips. The “stadium” package shown in figure 4 is one such option designed to increase basic chip packaging density that could equally be applied to RF or Opto applications.
Figure 4 – Three frame “stadium” package design
PACKAGE EXAMPLES
The main process for pre-molded frame parts is the insertion of a functional plastic cavity around a formation of metal lead ‘fingers’ to which connection of single or multiple chips and/or other components may be made. The cavity itself can be shaped, round, square and can have multiple depths depending upon application and chip designs. The exterior of the cavity can also be shaped as required or incorporate features to house external leads or mountings. The possibilities are endless.
For RF applications, the package requirements of thermal management and electrical isolation have now been achieved in pre-molded frame devices using the 2-frame process with high temperature LCP mold compounds. The device detailed in figure 5 is a design developed for 5
- 10 watt power RF transistors. The device is similar in dimensions to “off the Shelf” ceramic parts but is supplied in leadframe strips for use in automated assembly. This approach contributes to a factor 10+ manufacturing cost reduction for a range of devices.
Figure 5 – RF 5 Watt package
(Courtesy of Ericsson Microelectronics )
Adaption of leadframe technology to other RF applications is ongoing where pre-plated frames are insert molded with high temperature
LCP so that applications for power devices up to 150 watt are possible. Here the mold compound is used to isolate the main pad from power lead connections in the same plane.
Utilising a stamped leadframe and molding 16 parts in a single shot provides some of the cost advantage. Strip leadframes are used in magazine to magazine assembly lines and a low cost thermoplastic cavity lid is also included when non-hermetic sealing is used.
Matching function to environment can provide novel housing solutions. One of the most important package developments for the opto market has been the application specific designed Opto-Encoder as shown in figure 6.
This unit was designed to fit in an encoder module for a steering position sensor in the automotive market. Key factors for this were the need to assemble detectors and emitters in the same environment and provide features to ensure accurate alignment, the same requirement needed for “photonics” packaging.
The cavities are mechanically located to each other after the electronic components are assembled and tested. The manufacturing process is fully automatic.

Figure 6 – optical encoder assembly
A recent design exercise for a Fibre optic transceiver application has explored the use of all the techniques discussed to develop a low cost package to replace machined metal cavity units. This design runs 2 leadframes and molds a deep cavity around a heatsink base. The second frame, for the electrical I/O connections is molded into the side walls of the cavity at the same time. The smart thinking for this design is to build part of the fibre connector into the package lid, which will then interlock with the other part which is designed as part of the package wall. The lid is an injection molded part meeting the same high tolerances for dimensional accuracy as the cavity package.
CHALLENGES ONGOING
As the demand for optical devices grows, the capability to provide higher performance characteristics such as heat transfer and hermeticity in ’plastic’ packaging has become an issue in search of a solution. As previously discovered (3) the major challenges to packaging and assembly of emerging technology devices remain:
•
Alignment of components
•
Substrate/Material selection
•
Thermal management
•
Sealing
The alignment of optical parts in particular is the biggest challenge for dimensional accuracy.
For small mold devices tolerances can be kept very tight and accuracies down to 1 micron are achievable. The knock on effect for such parts comes down to getting associated tolerances to match in the feed and take up equipment necessary for high volume production.
Materials for molding the cavities are improving as suppliers develop new compounds. Conduit is so far unique to HHEM and a number of tests, being run with selected applications, need to be completed before production can be undertaken. The compounds used also determine the dimension accuracy achievable. New materials as well as new processes are likely to be necessary for sub micron tolerances.
Thermal performance is not only determined by leadframe materials and thickness but also by the compounds used for molding, especially in RF products. These need to have higher melting points to withstand the chip assembly processes yet provide a good thermal conduction to prevent stress and delamination around the metallic structures.
Hermeticity and Sealing of these types of packages are factors which are receiving the most attention. Thermo-plastic compounds such as ABS or PBT’s mold well but are not renowned for sealing around metal leads.
Newer materials like LCP are rougher in surface finish but give good seals and can achieve JEDEC level 2 packages. Figure 7 shows a Camera chip package design that after assembly with a sealed clear glass lid meets
Level 2. However level 1 is the demand for many of the Photonics applications. New liquid sealants can provide solutions but add an extra process step and cost to the assembly.
The challenge ultimately will be to seal the chips (as in direct die attach devices) and other components before assembly so that hermetic packaging is not needed, hence keeping costs down.
Figure 7 – 20L “Opto” cavity packages in strip form

Overall package sealing is dependant upon the chips and other structure within the cavity.
Hysol type filler compounds can really close up cavity packages to Level1, but are useless with MEMS, optical sensory and fibre components. Lids can be plastic or metal depending upon the system need. Plastic lids can be designed for glues and epoxies, snap in, where epoxy chemicals are an issue, weldable and /or functional capability. Depending upon materials selected, especially for cost considerations, new lid sealing compounds now being introduced are in need of evaluation for both RF and Photonic package applications.
FUTURE CAPABILITIES
The cost factor being the major drawback to volume take-up of any products, the aspects of low cost package solutions as detailed above are becoming the drivers for the new technologies such as required for “last mile” fibre optic telecom systems, 3G phones,
Bluetooth and Wan/Lan applications. Devices are needed at lower costs and in higher volumes. Thermoplastic mold compounds with pre-plated leadframes will inevitably be one of the most viable solutions for such low cost cavity packages.
New thinking for the design of application specific packages is the key for cost effective packaging. Why have a molded connector at the end of a transceiver fibre pigtail. Why not use the package as the connector with a cavity for the photonic circuit all in one molded housing? Why not have multi level substrates for packaging different types of chip components with fixed cavities for the optical interfaces all part of the package.
The capabilities of materials and design are being continually developed to match the electronics markets philosophy – Smaller,
Faster, Cheaper. It is now evident that Premolded frame technology can meet the demands of emerging technologies and will continue to match development needs for future applications.
ACKNOWLEDGEMENT
The authors are indebted to the support of
Ericsson Microelectronics for their assistance in the development of some of the technology described for RF packages and are grateful for their permission to release the information.
They also acknowledge the assistance of the engineering and design staff at HHEMG for their contributions to this paper.
REFERENCES
(1) Carla Miner,Nortel, Trends in Optoelectronics
– consequences for SEMI, SEMI Standards conference, Dresden, 25-27 October 2000.
(2) Kyocera Corporation – Packaging networks
2000 – Sales and Marketing presentation OEsalestool Rev 1.
(3) Steve Riches, Micro Circuit Engineering,
Practicalities of Opto-Electronic Packaging,
IMAPS UK Opto-Hybrid Microelectronics
Conference, IOP, 12 October 2000
(4) Ericsson Microelectronics website: http://www.ericsson.com/microe/products/rf_p ower_transistors.shtml