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Click here to learn about hermeticity
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Click here to go to our page on microwave circuit card assemblies
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Click here to go to our page on cost versus performance of soft substrates
Learn how to avoid oscillations in microwave packaging.
Microwave packaging is often broken into two broad categories: modules (often called hybrids) and circuit card assemblies. The intent of the two approaches is best summarized as this:
Microwave modules
Below are further definitions that will show distinctions between various categories of microwave packaging. One of the big distinctions between various packaging methods is whether or not hermeticity is provided; hermetic sealing of active devices in inert atmosphere extends reliability and is often a requirement for military systems.
Multi-chip modules: these combine two or more chips (integrated circuits) into a more complex circuit. Often an MCM is a non-hermetic package. And often, the distinction between MCM and Hybrid is blurred.
Hybrid modules: hybrids combine chips (discrete or monolithic), interconnect substrates, and passives (resistors, inductors and capacitors) into one module. Hybrid construction usually implies that hermeticity is provided. Feedthroughs are used to connect signals into/out of the housing yet maintain hermeticity. Often, the housing is fabricated from low-expansion alloys. in other cases, aluminum is used. Lids are hermetically welded on with laser or seam sealers.
Microwave Integrated Circuit (MIC): here a circuit is constructed from discrete devices (transistors) into a larger circuit such as an amplifier. MIC refers more to a method of construction, than a type of packaging (such as hybrid module). The "classic" MIC circuit is a balanced amplifier which contains two identical transistors, a pair of Lange couplers, and suitable blocking capacitors and bias elements such as resistors and inductors. An MIC circuit can often be replaced with an MMIC (monolithic microwave integrated circuit). Back in the day when MMICs were a new technology, supporters of MIC said that no matter what, they could always wrestle better performance from a device than a MMIC designer could. Today, MIC construction has almost been completely replaced with MMICs, because increased functionality is only possible though massive integration.
Chip-and wire: chip and wire refers to a method of construction, which is the basis for MIC circuits and hybrid modules alike.
Thin-film:
Thick film:
Cofired ceramics come in two flavors: low temperature (LTCC) and high temperature (HTCC).
Printed circuits
Here's a new website that exists only to manage a database of all PCB (PWB) manufacturers. Check out PCBDirectory.com
Microwave circuit card assemblies:
Printed wiring boards form the "substrate" for CCAs. Here's a page that offers PWB hints.
Millimeterwave packaging
Millimeter-wave packaging has its own page.
RF interconnects to chips
RF interconnects to chips include
Reliability:
Electrostatic discharge: no matter how you package electronics, ESD is something to consider.
Relevant books for microwave packaging
Here's a book recommendation for the topic of packaging:
Advanced Electronic Packaging, by Richard K. Ulrich and William D. Brown is an encyclopedia effort with a treasure-trove of information on various material's parameters, different interconnect schemes, design, fabrication and assembly of hardware, not just microwave (which we consider a plus!) Look for it soon on our book page.
If you are developing prototype modules in a lab, chances are you will take a lot of short cuts and not worry about half the stuff on this page. But if you intend to design something for production, you should learn as much as you can about production packaging processes.
A really great book on packaging is Advanced Electronic Packaging, by Richard K. Ulrich and William D. Brown. It is one of the best "encyclopedia" efforts we've seen, and we've seen a lot of lame ones. Look for it on our book page.
Some possible future topics:
Advanced interconnects such as flip-chip
Near-hermetic packaging