Aug. 12, 2002 – Munich, Germany – Infineon Technologies claims to have found a way out of the “impending wiring crisis of the semiconductor industry.”
Researchers have developed a technique to solder different types of ICs together to form a “sandwich” chip system, packing more capability into the same area as a single chip and creating high-speed connections that allow an increase in complexity while reducing costs.
For a first sample Infineon produced the upper and lower modules of these new sandwich chips in Dresden, Germany, demonstrating the feasibility of the new approach to a problem the industry has tried to solve for ten years. The technique uses standard chipmaking and packaging machinery to take a step forward in chip integration. The soldering technique, called SOLID, combines the multiple chips in a single package to create a single product. The technology promises both to speed up chip performance, and to help reduce the price of current chip solutions by up to 30%, Infineon claims.
In all semiconductor-based applications, such as mobile phones, multiple chips exchange electronic signals using fine wires laid out precisely on printed circuit boards. The longer the lines between the adjacent (planar) chips are, the more time an electrical signal needs to travel. This makes design more complex and can slow down the performance. Additionally, the number of possible circuit wires is strongly limited in a tiny space. As chips become more complex, a “wiring crisis” is making it very difficult and therefore expensive to implement applications that require high frequencies – such as communication technology – at the speeds required to satisfy design requirements.
According to Infineon, with the SOLID technology, the tracks between the contacts are much shorter. Interior contacts within a single chip package conduct signals directly between the individual segments of a chip. A SOLID product can achieve clock rates of up to 200 GHz (100 times faster than today’s fastest desktop PC processors) and support more communications lines between the chips in the package. Compared to existing chip systems, it is possible to pack hundred times the number of connections into the same space. This enables manufacturers of electronic equipment to use smaller printed circuit boards and thus to develop new and more cost-effective products. Soon systems will be created that handle complex tasks much faster in less space.
The name SOLID is derived from the soldering process used, which is diffusion soldering (the exact term is solid-liquid interdiffusion). Prior to soldering, the upper and lower sides of the “sandwich” chip are coated with a very thin layer of copper. The solder is applied with a thickness of only 3 µm (1 micrometer is one thousandth of a millimeter). Both chips are then soldered together at a temperature of 270°C and 3 bar of pressure to create permanently bond. The combined chips will not be higher than “normal” chips because flat (“thinned”) silicon wafers are used as a basis. These silicon wafers usually have a thickness of 120 µm. For SOLID products, Infineon will reduce them to only 60 µm in a cost-effective standard process. This corresponds approximately to the diameter of a human hair. The “chip sandwich” is provided with the same outer layer for semiconductor components made of compound material and plastic as normal chip systems – this allows a savings of up to fifty per cent of the material and the cost for packaging.
The new technology is suitable for almost any semiconductor application, Infineon said, from chips for mobile communications to industrial and automotive systems. Existing products can be made with up to 30 per cent less cost through the more effective utilization of production facilities – for example by producing the highly complex upper sides and the less complex bottom sides of the ‘sandwich’ chip separately. A chip that is manufactured with the SOLID process also requires up to 50% less space than conventional products with the same functionality that are arranged side by side. The shorter tracks reduce the power consumption, which results in a lower operating temperature. With these features, the SOLID technology provides more convenience for the use of mobile phones and notebooks because the batteries last longer and the mobile devices become not as hot as today’s products.
The first prototype being produced in the new technology is a smartcard controller. Current smartcard controller products combine both a logic chip and memory chip on a single planar surface. Therefore the controller has only a limited memory capacity, typically 32 Kbytes of memory. A first prototype of a smartcard controller manufactured by Infineon using the SOLID process has 160 KBytes of non-volatile memory. This means that it is not only possible to store more data on the chip but also that the working smartcard can use a more complex, operating system and execute more software applications.