Package Diversity
By Casey Krawiec, StratEdge

Perhaps the most important component of a semiconductor package company’s business strategy is diversity. Successful package companies have a diversified portfolio of products to offer to their customers. To have long-term success, companies should have a variety of manufacturing technologies, diverse construction techniques, and more than a few markets for their packages.

One of the consequences of not being diversified is that the company becomes a one trick pony. You may be the best company on the planet making purple packages, but what happens when the markets for purple packages go away? History has shown that the package requirements of semiconductor companies definitely change over time. Do those of you who are old enough remember the migration from pressed ceramic with frit seals to plastic encapsulated packages in the memory chip market? Remember when packaging of central processing units (CPU) moved from co-fired ceramic to plastic laminate packages? Former employees of Alcoa Electronic Packaging sure do. Alcoa closed its San Diego plant in 1996 within months after Intel announced the switch from ceramic to plastic packages for its microprocessors. Alcoa essentially had one package technology, multilayer co-fired ceramic; one construction technique, pin grid arrays (PGA); and one market, CPU. Alcoa most certainly had all of its eggs in one basket and 1,200 employees suffered from its lack of diversity.

For package construction, who isn’t aware of the rise and fall of some package styles? Look how surface mounted components have replaced through-hole for board mounting. Dual in-line packages (DIPs) and co-fired ceramic side braze packages are still manufactured, but at a fraction of the numbers made in their heyday. More recently, we have seen packages with ball grid arrays (BGA) replace PGAs. Metal cans for diodes and hybrid bathtub packages with glass feed-throughs may never go completely away, but most of the companies who specialized in making them certainly have.

The shift from ceramic to plastic in CPU packages has already been mentioned. The product life cycle for the packaging of a chip used in commercial applications routinely follows this path from ceramic to plastic. Performance is proven in a ceramic package and the product gets introduced to the market. If the product is successful, demand increases and the ceramic package company expands capacity. Then there is market saturation. Demand for the product rapidly decreases, everyone in the supply chain accumulates too much inventory, and profit margins erode. While layoffs occur, engineers have to figure out how to get acceptable performance out of plastic packages. If successful in lowering the cost by using plastic, the revised product is introduced and the company remains a player in the market.

So, cost usually drives the shift from ceramic to plastic. The pennies one can save using plastic packages add up in applications where millions of units are being produced. For low power, low frequency applications, one can usually use plastic packages and get the required performance. But it’s not so easy if it’s a high frequency or high power application. It might not be possible to get good enough performance using plastic, which is why ceramic package companies can still be successful.

How do companies diversify their package offerings? They look at the requirements of the market and they develop package solutions that meet those requirements. Applications drive innovation. For example, StratEdge designs and manufactures ceramic semiconductor packages for microwave, millimeter wave, and high speed digital devices. When it was founded almost twenty years ago, its package portfolio was not at all diverse. In fact, it was quite limited. The target market was military and space customers wishing to package Gallium Arsenide (GaAs) chips in high reliability packages. For this one application, a revolutionary design concept was developed that employed layers of post fired alumina ceramic with continuous gold traces laminated together and brazed to a copper composite heat sink. Sealed by a metal lid with solder, these fully hermetic ultra low loss packages were perfect for applications where high reliability and superior electrical performance were essential.

For better or for worse, package requirements tend to vary greatly application to application. Semiconductors come in many different quantities, sizes, shapes, and materials, and with many different performance requirements, thermal requirements, environmental requirements, numbers of interconnects, and on and on and on. Look at material differences alone. What is the insulating material in the chip and how does it act? How does it expand and contract when it heats and cools? How much and at what rate? How well does it conduct the heat generated by the transistors in the chip? Does the backside need to be grounded electrically? And what about the conductive traces? What material are they, how will they be connected to the package, and what is the level of reliability required of the interconnects? The point here is that one package style will never fit all applications. The semiconductor industry screams for a diverse product offering from package manufacturers.

Both plastic and ceramic package manufacturers have had to adapt their packages to accommodate new applications. The multitudes of package parameters that have been modified or improved over the years are too numerous to list in this short article. To illustrate this point, the following are examples of how ceramic packages for high frequency applications have changed over the past twenty years. Included are a sampling of ceramic packages that are currently available, their construction, the types of devices they are designed to protect, and the applications where they are used.

Although the original ceramic packages worked great for space and military markets, more applications with different requirements arose. GaAs semiconductor technology matured and it was adopted in various commercial applications. A greater variety of packages were needed. The new packages had to be more economical and their construction changed to accommodate high volume assembly techniques. They also had to be adapted to the frequency ranges of different applications.

One new design requirement for ceramic microwave packages was that they needed to be leaded. Originally for VSAT applications, a leaded power amplifier series of ultra low loss leaded packages was designed. These packages use thermally conductive copper composite bases that can dissipate the heat generated by the devices and match their rates of thermal expansion. The metal base and leads are attached to an alumina ceramic ring frame with copper silver braze, a high temperature (> 600 degrees C), high strength material that provides fantastic reliability. To protect the device, a plastic cup-shaped lid was designed to seal the package with a b-stage epoxy preform. These packages are mounted into cutouts in the board where they are bolted in place and the leads attached with solder. The leaded construction provides easy and cost effective attachment to the next level of the system without sacrificing electrical performance so critical for high frequency performance.

Surface mount designs are required for some applications, so package companies diversified to meet this demand. Unlike packages that are mounted in a hole in the circuit board, surface mount packages mount directly on the board, reducing circuit board assembly costs. Surface mount packages also simplify the board layout and significantly reduce board design costs. For power amplifiers, these packages incorporate a conductive metal base attached to an alumina ceramic ring frame and their leads are co-planer with the thermally conductive base. The base and the leads are attached to the package using high temperature copper silver braze. These packages are sealed using a cup-shaped lid with a b-stage epoxy preform. The copper composite base is smaller and thinner than the bases in most ceramic package designs, so they are less expensive than other flanged packages with large metal bases. The performance range of these packages makes them ideal for next generation test and measurement equipment, WiMax and VSAT amplifiers, point-to-point and point-to-multipoint radios, and any high power application where surface mount packages are desired.

An obvious requirement for new packages was that they needed to operate at higher frequencies, so a series of drop-in packages with ultra low loss performance were introduced. With a thermally conductive copper composite base, the package provides superior electrical performance even in thermally stressful environments. These packages are mounted into cutouts in the board and connected with ribbon bonds to achieve the ultra low loss connections. A plastic cup-shaped lid is used to seal the package with a b-stage epoxy preform. Because of their broadband performance, extremely low electrical loss, and ability to handle wide temperature variations, these versatile packages are used in a variety of applications. These include point-to-point and point-to-multipoint radio applications where the packages must protect the broadband, high power amplifiers. Their ability to maintain signal integrity makes them ideal for low noise amplifiers (LNAs), phase shifters, and switches.

Innovation within a company is one way to diversify. Another way to diversify the portfolio is through acquisition, as was common in the booming 1990s. StratEdge acquired molded ceramic package expertise by purchasing Package Technologies Incorporated (PTI). Molded ceramic packages are made using a technological derivative of the old glass-to-metal seal process. These new packages augmented the company’s product line well. They were a lower cost alternative to the existing packages, while providing good electrical performance in the DC to 15 GHz frequency range. With their hermetic seal lids, they’ve been popular choices where high reliability is key. The most successful applications for these packages have been in long haul telecom, test equipment, and military markets.

Several other types of packages are available from ceramic package manufacturers. One such package is the power package, as seen in Figure 1. It can be used with silicon, silicon carbide, gallium nitride, and other applications for power integrated circuits. It is constructed with thermally conductive beryllium oxide (BeO), which gives the package excellent thermal properties. Power packages are available in industry-standard outlines. They provide superior electrical performance and incorporate copper composite bases for enhanced thermal dissipation. Hermetic packages in this series are sealed with metal or ceramic lids that have gold-tin solder preforms. The non-hermetic version is sealed with cup-shaped ceramic or liquid crystal polymer lids with b-stage epoxy preforms.

“The quality of a package’s construction is directly proportional to the performance of the chip,” explains StratEdge senior applications engineer Jerry Carter. “The package used determines if the chip will perform to the specifications of its design. High frequencies and high heat put new demands on package manufacturers for quality and reliability, yet the new packages still must fit industry-standard outlines.”

Figure 2 shows a fully hermetic, true low profile, molded ceramic surface mount package. The packages handle frequencies from DC to 20 GHz, providing excellent electrical performance. They are designed for use in the aerospace, avionics, and telecom industries and to package LEDs, MEMS, and optical devices. The package is most often sealed with a metal lid and gold-tin solder preform, making it MIL-STD-883 hermetic. They come in industry-standard footprints. Molded ceramic packages combine post fired ceramic and molded ceramic, two mature technologies used in several types of packages.

Hermeticity has been required for various applications over the years, and now many more packages are available with that option. It’s been difficult to produce a hermetic package that protects the electrical integrity of the chip while handling the thermal requirements and providing high reliability. However, using glass lamination and metallization has resulted in the ability to make hermetic versions of some popular existing packages, as seen in Figure 3.

How far should a company try to diversify its core competencies and risk overwhelming its technologists? A company may try to be all things to all people, but there are potential problems. A company should be concerned that it will become good at only doing a few things, but great at nothing. Or perhaps, because their resources are so diluted, they aren’t even good at doing anything. There are a few large package companies with tremendous resources who can get their arms around all of the package technologies. For various reasons, they seem to have aligned themselves according to the insulating materials used in the packages. There are those in the organic camp, aka plastic, and there are those in the inorganic camp, mainly ceramic. Apparently, what makes a company good at spitting out ceramic packages doesn’t translate to plastic packages, and vice versa. That’s where the line is drawn in the sand for diversification. Because semiconductors come in all shapes and sizes, it appears there will always be room for both organic and inorganic packages. Within those subgroups, successful companies will have a diverse product offering so that they are positioned to offer solutions for new opportunities and shift to greener pastures when their pastures turn brown.

StratEdge
www.stratedge.com
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