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[Pins & Vias] Complex Hybrids from New Materials
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As more circuits get crammed into smaller spaces by the latest semiconductor process technologies, the IC package is becoming a key consideration in the design and manufacture of a wide variety of electronic systems. This is especially true when it comes to the problems designers face in attempting to cope with not only the electrical and mechanical properties, but the thermal and power management aspects of high-density, high-speed, and often high-frequency circuits that must coexist on a substrate.
Hybrid multi-chip packaging technology is being used to deal with these issues in industrial, communications, aerospace, automotive and military applications, but the techniques of their manufacture are undergoing transformation as new materials come to the fore. Some designers of very high-speed telecom and datacom systems are finding new ways of using the classic advantages of low-temperature co-fired ceramics (LTCC) in certain communications applications, but are combining these materials with newer, subtractive thick films and etch techniques.
Others are completely abandoning older hybrid types based on thick-film methods for screen printing conductor, resistor and insulator inks on ceramic substrates. Instead, they are switching to new organic thick-film etch and substrate materials, in order to achieve very fine line widths and spacing for high-density, high-performance, low-cost applications. Another emerging substrate material, steel, has some of the same advantages of ceramics but with even better thermal properties. In addition, it is especially suited to ensuring electronics security in industrial, aerospace, automotive, scientific and military systems, since its properties, including its novelty, make it very difficult to reverse-engineer.
The complexity of materials issues, and the issues resulting from combinations of varied materials, are arising because of the classic use of a hybrid multi-chip package to combine both active and passive components, which often have radically different packaging needs in terms of physical, electrical, and thermal requirements. In addition, there is the increased use of multi-layer dielectrics, and the fact that, as circuit and component density increases, tolerances for such metrics as glass transition temperature, thermal conductivity, and thermal coefficient of expansion become much tighter.
Materials Decisions
Ceramic hybrid packaging materials are still finding a home in many military and industrial applications that are suited to LTCC substrates, combined with thickfilm printing techniques. Ceramic substrates also give exceptional performance in small RF modules in cell phones, as well as certain automotive applications, and as lightweight power supply modules. These materials are also suited to many high-frequency applications because of their low signal losses at high wireless and broadband frequencies. However, even though their superior mechanical rigidity gives better electrical properties over a variety of operating temperatures, that very rigidity can become a problem in some design contexts. In addition, their superior thermal conductivity can be a handicap compared to organic laminate materials, especially in the tight tolerances of high-I/O ball grid array (BGA) packages.
Many chip makers have been steering away from older ceramic substrates, primarily because of their expense and comparative inflexibility. In contrast, many of the most advanced organic laminate materials have lower dielectric constants, as well as superior power distribution and signal transmission for the chips packaged inside them. Some new hybrid packages may even combine multiple materials, such as epoxy glass, polyimide glass, silicon, and flexible metallized polymers, occasionally with ceramics.
Hybrid multi-chip packages are considered by many designers as ideal candidates for combining the mix of optical, RF, analog and digital technologies required in the next-generation of leading-edge, ultra high-speed fiber optic modules. But when it comes to the ideal materials to be used in these hybrids, the jury is still out. Some manufacturers of advanced organic laminates insist that these substrate materials, which have been proven in GHz-speed Internetworking applications, are the best for the extremely complex packaging design rules of optoelectronic components. But ceramic substrate manufacturers such as Dupont Microcircuit Materials, Research Triangle Park, North Carolina, argue that the LTCC substrates and thick-film etch materials which have been proven in both highperformance, low-volume military and space applications -- as well as high-volume, cost-sensitive wireless communications and automotive applications -- are much better suited to high-speed fiber optics uses.
By Andrea McCormick
(April 2002 Issue, Nikkei Electronics Asia)
Hybrid multi-chip packaging technology is being used to deal with these issues in industrial, communications, aerospace, automotive and military applications, but the techniques of their manufacture are undergoing transformation as new materials come to the fore. Some designers of very high-speed telecom and datacom systems are finding new ways of using the classic advantages of low-temperature co-fired ceramics (LTCC) in certain communications applications, but are combining these materials with newer, subtractive thick films and etch techniques.
Others are completely abandoning older hybrid types based on thick-film methods for screen printing conductor, resistor and insulator inks on ceramic substrates. Instead, they are switching to new organic thick-film etch and substrate materials, in order to achieve very fine line widths and spacing for high-density, high-performance, low-cost applications. Another emerging substrate material, steel, has some of the same advantages of ceramics but with even better thermal properties. In addition, it is especially suited to ensuring electronics security in industrial, aerospace, automotive, scientific and military systems, since its properties, including its novelty, make it very difficult to reverse-engineer.
The complexity of materials issues, and the issues resulting from combinations of varied materials, are arising because of the classic use of a hybrid multi-chip package to combine both active and passive components, which often have radically different packaging needs in terms of physical, electrical, and thermal requirements. In addition, there is the increased use of multi-layer dielectrics, and the fact that, as circuit and component density increases, tolerances for such metrics as glass transition temperature, thermal conductivity, and thermal coefficient of expansion become much tighter.
Materials Decisions
Ceramic hybrid packaging materials are still finding a home in many military and industrial applications that are suited to LTCC substrates, combined with thickfilm printing techniques. Ceramic substrates also give exceptional performance in small RF modules in cell phones, as well as certain automotive applications, and as lightweight power supply modules. These materials are also suited to many high-frequency applications because of their low signal losses at high wireless and broadband frequencies. However, even though their superior mechanical rigidity gives better electrical properties over a variety of operating temperatures, that very rigidity can become a problem in some design contexts. In addition, their superior thermal conductivity can be a handicap compared to organic laminate materials, especially in the tight tolerances of high-I/O ball grid array (BGA) packages.
Many chip makers have been steering away from older ceramic substrates, primarily because of their expense and comparative inflexibility. In contrast, many of the most advanced organic laminate materials have lower dielectric constants, as well as superior power distribution and signal transmission for the chips packaged inside them. Some new hybrid packages may even combine multiple materials, such as epoxy glass, polyimide glass, silicon, and flexible metallized polymers, occasionally with ceramics.
Hybrid multi-chip packages are considered by many designers as ideal candidates for combining the mix of optical, RF, analog and digital technologies required in the next-generation of leading-edge, ultra high-speed fiber optic modules. But when it comes to the ideal materials to be used in these hybrids, the jury is still out. Some manufacturers of advanced organic laminates insist that these substrate materials, which have been proven in GHz-speed Internetworking applications, are the best for the extremely complex packaging design rules of optoelectronic components. But ceramic substrate manufacturers such as Dupont Microcircuit Materials, Research Triangle Park, North Carolina, argue that the LTCC substrates and thick-film etch materials which have been proven in both highperformance, low-volume military and space applications -- as well as high-volume, cost-sensitive wireless communications and automotive applications -- are much better suited to high-speed fiber optics uses.
By Andrea McCormick
(April 2002 Issue, Nikkei Electronics Asia)
