Innovative packages for STx86 processors

SGS-THOMSON Microelectronics has announced two innovative packages for its STx86 family of microprocessors that provide substantial advantages over the ceramic pin grid array (CPGA) packages traditionally used to house microprocessors for desktop PC applications. The Plastic PGA (PPGA) and Power Plastic PGA (P3GA) packages are fully compatible with existing sockets and handlers but offer lower cost and better thermal dissipation.

"This is a breakthrough packaging technology for the x86 market and the PPGA will allow designs in portable PCs" said Daniel Queyssac, Vice President of SGS-THOMSON's New Ventures Group and who personally spearheaded this programme. He added: "The fact is, the PPGA reduces the x86 packaging cost by a factor of two, compared with the CPGA alternative, and the P3GA slightly better compared to CPGA plus heatsink solution.

"This packaging breakthrough combined with our aggressive silicon technology programme (see related press release) is what our customers expect from a leading manufacturer of high volume, high quality, cost-effective devices and these are facts to our commitment to the STx86 family", he added. The PPGA will ship in December on the ST486DX family and in Q1 on the ST5x86 family while the P3GA will be targeted for shipments on the ST6x86 family.

The new packages are patented and the fruits of the synergy between SGS-THOMSON's PC Micro activities and its renowned power packaging expertise; although the concept of the plastic PGA package is not particularly new, advances in laminate technology, encapsulation materials and pin attachment enable the new plastic PGA packages to dissipate more heat than their more expensive ceramic counterparts.

Both new packages have the same basic structure in which a multi-layer laminated board provides the interconnection between the chip wires and the array of package pins fixed in the moulded base. The PPGA package features a flat aluminum cover plate to which an external heatsink can be attached, while the P3GA contains an integrated finned aluminum heatsink.

Because the large metal plate (or finned heatsink) spans the entire package and the chip is attached directly to the aluminum, the new packages feature outstanding heat dissipation. For example, using a 168-pin PPGA housing a 9mm chip, the thermal resistance from junction to case is reduced from 2.5°C/W for a ceramic package to only 1.5°C/W, while the heat spreading effect of the aluminum allows even more significant reductions to be made in the junction-to-ambient thermal resistance

In terms of electrical performance, plastic PGAs offer a number of potential benefits - for example, the PCB etching techniques used allow smaller track widths and closer spacings than the thick film processes used in ceramic PGAs, which provides greater flexibility and more control over electrical characteristics. In addition, the dielectric constant of the PPGA laminate is typically less than half that of the alumina used in CPGAs, while the conductivity of the copper used in plastic PGAs is typically three times that of the tungsten used in co-fired ceramic construction. This can be particularly significant in high current applications or where low supply voltages are used.

The new packages are particularly suitable for the highly competitive x86 market, where packaging is now a significant factor in manufacturing costs but compatibility with existing sockets and automated assembly equipment is essential. However, they will be equally advantageous in other areas involving high complexity digital ICs.

STx86 microprocessors complement a vast family of SGS-THOMSON devices that are raising performance standards in every area of the PC. For example, SGS-THOMSON devices can be found on PC motherboards , in monitors, disk drives and multimedia add-ons. In fact, there are probably more SGS-THOMSON chips in more PCs than any other x86 manufacturer. SGS-THOMSON can offer customers a rich product portfolio for computer and multimedia applications, ranging from ultra-fast burst RAMs, to MPEG decoder ICs.

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