The first concept for a printed circuit board (PCB) was developed in the 1930s. The concept became commercially viable by the 1950s, and since then, PCBs have moved into just about every phase of our lives. They surround us, and have changed out lives in many ways. In the 2000s, trace was reduced to 3.5-4.5mil, and Flex and Rigid-Flex PCBs proved innovative. The ability of engineers and designers to use PCBs to infiltrate our lives continues on an ongoing basis.
Moore’s Law suggests that the number of transistors in a dense integrated circuit doubles approximately every two years. Moore made this claim in in1965. In the early 1970s, the RCA1802 was state-of-the-art, and able to deliver a whopping 2,500 transistors. Moore’s Law was shown to be validated when the Pentium chip was released in the mid-1990s, delivering five million transistors (5×106). 2010 saw the release of the Quad-core Z195, with 1,000,000,000 (1×109) transistors.
Based on Moore’s Law, we can anticipate chips having the capacity to deliver 6 x 1010 transistors by 2020. If that is to happen, then miniaturization will continue, unabated. The PCB industry will be challenged in basic process capability and in material properties to allow for ongoing developments that deliver improvements ininterconnection density and electrical performance. Moore’s Law has shown itself to be valid for the last 50 years, but if this is to continue to be the case, new concepts will need to be incorporated into PCB design.
Some current innovations in PCB design provide some insights into how those developments are happening. Some new developments that are facilitating this include Every Layer Interconnected (ELIC); High Density Interconnection (HDI).
ELIC design uses a method of stacking microvias on every layer. It provides the opportunity for dynamic connection between anytwo layers in a PCB. The level of flexibility provided by such a design maximizes the area available for use in dense component placement. It also provides increased circuit density when designers are faced with complex challenges in routing.
HDI is based on continually reducing in feature size the spacing and conductor width of trace, micro-via diameter and pitch. The aim inevitability is to incorporate more components and layers without compromising the size, weight or volume of the PCB. The electrical performance of the PCB will continue to be challenged by increased wireless bandwidth and increased processing speeds. However, there are concerns regarding the cost-benefit of incremental developments. One challenge is ensuring dimensional stability as individual isolation layers are reduced in thickness to 50 microns or less. Electrical performance is also affected, as signal performance and resistance to leakage are challenged at this level.
In addition to the use of HDI and ELIC, innovations include high aspect ratio products, high performance pulse plating copper, and the application of plasma technology. As each of these technologies are incorporated into PCB design, miniaturization will continue, and Moore’s Law may continue to be validated over the coming years.