TOKYO -- OKI Printed Circuits has built what it is calling the world’s-first mass-production technology for "super multilayer" printed circuit boards of 102 layers apiece.
Mass-production of the 480mm boards, which are 6.8mm thick, will begin in October. They will be used for probe cards to test wafers for DRAMs and NAND flash memories.
"We are delighted to develop the proprietary Low-resistance Impedance Controlled Technology, a state-of-the-art technology allowing as many as 102 layers with maximum board thickness of 6.8mm,” said Hiroshi Shimada, president of OKI Printed Circuits. “This LICT makes low trace resistance and characteristic impedance control based on an optimized form of ground layer artwork right beneath the signal trace.”
As LSI manufacturing processes become finer and wafer diameters expand, DRAMs and NAND flash memories incorporate more and more IC chips per wafer. The number of LSI chips tested by wafer testing, which is executed in front-end LSI process, continues to expand. This trend means probe cards, which electrically connect an LSI tester and a wafer, must incorporate more signal traces and power supply traces.
To allow mounting on wafer testing equipment, probe cards must be produced to specified thicknesses or less. This means layer-to-layer distances must be significantly smaller to account for the growing numbers of layers. With existing production methods, smaller layer-to-layer distances affect signal characteristics, including characteristic impedance and trace resistance. Eighty layers have been regarded as the limit for printed circuit boards for probe cards that provide the high-precision signal characteristics required. Producing circuit boards with numbers of layers exceeding this figure has posed major challenges.
The technologies underlying LICT include high-accuracy electromagnetic field analysis and automatic editing of ground layer data. Compared to existing technologies, these technologies enable 30% lower trace resistance without degrading signal characteristics while enabling high quality signal transmission required to produce probe cards with improved wiring capacity. In addition, leveraging general High-Tg FR-4 rather than requiring special materials leads to cost effectiveness.