Fueling the Next-Generation Packaging Revolution
Eric Bogatin, Contributing Editor -- Semiconductor International, 7/1/2001
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IBM, Siemens and Hewlett-Packard were the first pioneers to ship products in the early 1980s that used the core ingredients of HDI technology: non-mechanically drilled blind and buried vias, thin dielectric layers and fine lines.
Printed circuit boards were manufactured and ramped into volume production with interconnect densities almost an order of magnitude higher than could be obtained with conventional drilled through-hole boards.
Today, HDI substrates represent a $1.6B industry that is expected to grow to ~$8.6B by 2005, according to TechSearch International. HDI substrates are the mainstream solution for many products in high-volume production, and their proliferation into new products is accelerating.
Happy Holden, manager of advanced technologies for Westwood Associates, has classified HDI applications into three families: product miniaturization, IC packages and high-performance boards. In the first two applications, HDI is an enabler, allowing new products that have no alternative manufacturing method, while in the case of motherboards, it allows denser, faster and cheaper products.
Current-generation consumer products such as cell phones, camcorders and MP3 players are dense electronic systems with optical and audio interfaces. A useful metric to describe the functional density of a board is the number of I/O per square inch of the board. Many consumer products fabricated in Asia have I/O densities of 600/in.2, compared with drilled through-hole boards, which have 100/in.2 as the maximum practical I/O density.
The consumer product substrates are exclusively HDI, typically six to eight layers, with components populated on both sides. The fine features on the surface and high interconnect density allow the use of chip-scale packages with peripheral and area array pitch as fine as 0.4 mm.
| Intel Celeron flip-chip package composed of a six-layer HDI substrate on a PGA base. (Source: Intel) |
Take a conventional board and redesign it with HDI technology. It is commonly believed that the layer count will be less but the substrate may be more expensive. "Most people in North America think that HDI will increase costs. But this is only if you don't take advantage of the reduced size and increased density possible," Holden said.
The increased density possible comes from two sources. With finer features on the surface, finer pitch area array packages with 0.8 mm pitch I/O can be routed — this means more components on each side. With non-blocking buried vias, both sides of the board can be used for component attach. This translates into the ability to convert multiple boards into one board, and a dramatic reduction in the total cost of ownership of products incorporating HDI substrates.
Yes, there are still technical issues associated with the design, laminate material selection, via hole production technology, registration, metallization process, lamination conditions and stack-up. However, these issues stem from an overabundance, rather than a lack, of options.
According to Holden, the leading producers of HDI substrates are Japan, Taiwan, Europe, Korea and China, at 54%, 14%, 11%, 11% and 8% of worldwide production, respectively. North America produces less than 2% of the world's substrates with HDI layers. This will probably get even smaller as production continues to ramp in Asia.
For additional information on assembly and packaging, go to www.semiconductor.net/assembly
