Et Tu, Embedded Passives

I don’t know if or when embedded passives will become the “next big thing” in PCB design, but they are on the way. We at Screaming Circuits have been asked about the use of embedded passives a few times.

Embedded passives
The purported advantages of the technology lie primarily in the ares of cost reduction and space reduction. You could potentially get your bypass caps much closer to where they need to be as well. The space parameter is pretty obviously an advantage, but the jury is still out on costs. I suspect that at this moment, it’s pretty difficult to find a board house that can fabricate a PCB with embedded passives.

If you’re not familiar with the concept, capacitors or resistors are built up on the inner copper layers of the substrate. There are a couple different methods used such as plating, printing or thin-film. As shown in the illustration, the resistors and capacitors inside the PCB negate the need to mount them on the outside. I can see rework being a problem if any of those embedded parts has issues.

In terms of assembly, we wouldn’t treat such a board any different than any other PCB. If your fab house notes that there are temperature or any other restrictions, let your assembly house know. Beyond that, all the standard rules apply.

Duane Benson
Note from Forbin: Colossus is watching

One thought on “Et Tu, Embedded Passives

  1. Duane,
    It has taken 20 years for embedded passives to become the “next big thing.” Patents for the concept date back even farther, to at least 1985 (Leary and Silverio; USPTO 4,494,172). Jim Howard, then of Zycon, received a patent for informing how to create capacitance using a thin dielectric layer; that was later the source of some contention between Sanmina-SCI (which acquired the patent rights through its purchase of Hadco) and Howard himself:

    But, to the point, there is more than one way to skin this cat. Some embed components; others use novel materials from companies like Oak-Mitsui, DuPont, 3M and others. At one point, Sanmina had more than 50 licensees, I believe, of ZBC (Zycon Buried Capacitance), based on Howard’s patent.

    Insofar as embedding components, many companies have been doing this as well. It’s a little trickier, as far as I can tell, but is certainly in widespread practice. (Adoption of embedded components means the fab house needs HDI capability, too.) Today, even actives are being put inside the board. USPTO 7,116,557, (Raby, et al) describes a printed circuit board assembly comprising a primary core of thermally conductive material; a two-tiered laminate substrate with a cavity, and an embedded wire-bonded chip. This method has been used in a large number of US missile systems.

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