The expectation that embedded passives technology would be required to meet size, performance, and cost requirements of devices has been a driver of considerable R&D activity in laboratories of many material suppliers. In particular, the proliferation of multi-band, multi-function handheld devices surely should require that discrete components be integrated into the package to save space. This integration also minimizes routing distances for optimum package or module performance. Size reductions of up to 43% versus non-embedded designs have been reported.1
System designers are faced with balancing the value that each embedded technology brings with the consequences of new process introductions. Organic laminate technology offers the lowest cost/unit area for a given RF functionality. LTCC technology is intermediate in cost/unit area, but offers more embedded functionality in a smaller size than laminate. Silicon-based technology offers the smallest solution for the same functionality, but comes at the highest cost.2
Our scientists have been developing organic materials that expand the use of low-loss dielectric technology down to the sub-5μm thicknesses desired in packaging substrate layers. But so far, there seems to still be little market adoption of these materials. Each new generation handheld or wireless card continues to come out with just more of the same when it comes to incorporation of needed passive functions.
Open up the iPhone and find that discrete passive components are in fact multiplying inside these latest handhelds, not going away. In total, passive components seem to occupy over 40% of the iPhone’s PCB area.3 Granted, these discrete devices have gotten so small, only the daintiest of fingers or robots can pick them up. These ever-shrinking surface mount components seem to have enabled designers to continue to do more with less. The continuing size and cost reduction of discrete devices certainly is a major reason that embedding the passives has not become the norm. Some reading over in SMT Magazine tells me, however, that the issues with mounting these little specks onto the circuit board are requiring more precise and expensive equipment, putting downward pressure on yields.
Embedded inductors, capacitors, and resistors were first deployed around 1999, so the technology is not new. So what else may be holding up wider adoption of embedded passives into package substrates? The key bottleneck may be the lack of design experience and necessary design libraries that hinder progress. Since the passive element is no longer a discrete device with specified performance but rather a printed element on a circuit layer, there are no specifications available that characterize the element’s performance. Furthermore, when various elements are placed in close proximity, their fields may interact with each other and need further model refinement to fully predict performance. The learning curve may lead to lower yields in initial implementation attempts may discourage broader implementation.
Embedded passives have been the norm when you look at what is going on defense and aerospace. Here, the performance gains achieved are key and ceramics materials are the standard materials of choice typically processed in panels barely larger than the size of today’s semiconductor wafers. Design libraries have been developed by some of the individual players in these segments but are not broadly available and in some cases, maybe even classified. Even where the information is publicly available, the solutions are often too expensive for application in the commercial sector.
Commercial millimeter wave applications such as automotive radar, high frequency imaging and emerging potential of 60GHz wireless applications are driving embedding functions for the same performance reasons but are increasingly looking to organic materials as a way of increasing production scale and reducing total cost. It may be these emerging high-end commercial applications that will finally cause the chasm to be crossed between niche early adoption and broad commercial acceptance. In the meantime, we’ll continue to get ready to supply the materials to help make it happen.
REFERENCES
- Ulrich, Richard, Integrated Passives Component Technology and Commercialization, IPC Professional development Course, 2/23/04.
- Gaynor, Mike, Antenova, presented at RF SiP Technology and Capability Overview, 2008 IEEE MTT-S International Microwave Symposium, 6/17/08.
- Stratigos, Jim, “Shrink the iPhoneTM”, On-line editorial in Advanced Packaging, http://ap.pennnet.com/display_article/337103/36/ARTCL/none/none/1/Executive-Viewpoint/
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DIRK M. BAARS, director, advanced materials group, may be contacted at Rogers Corporation, 1 Technology Dr., Rogers CT, 06263; 860/779/4772; E-mail: [email protected].