Proprietary LICT structure achieves mass-production technologies for probe cards
A probe card
TOKYO – OKI Printed Circuits, an OKI Group company responsible for OKI's printed circuit boards business, recently succeeded in the world's-first development of design and mass-production technology for super multi-layer printed circuit boards realizing 102 layers, significantly expanding from past limitation, with a diameter of 480 mm and a thickness of 6.8 mm. Mass-production of probe cards(*1) using this state-of-the-art technology used to test wafers for the latest DRAMs and NAND flash memories is slated to begin in October 2015.
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(*2) 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.
"We are delighted to develop the proprietary Low-resistance Impedance Controlled Technology (LICT), a state-of-the-art technology allowing as many as 102 layers with maximum board thickness of 6.8 mm," says 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."
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(*3) rather than requiring special materials leads to cost effectiveness.
*1 :Probe card
It is a device used in wafer testing process of IC manufacture to electronically connect an IC tester and an IC electrode on a silicon wafer. Probe pins for connection to IC electrodes are attached to a base printed circuit board.
*2 :Characteristic impedance
Characteristic impedance is the ratio of voltage and current on electrically conducting lines used to transmit electronic signals. Differences in characteristic impedance along a transmission line can generate reflection noise, degrading signal quality. Characteristic impedance is determined by the layer-to layer distance (or thickness), the width and the thickness of the signal trace, and relative permittivity of dielectric material.
*3 :High-Tg FR-4
It is a printed circuit board material with excellent heat resistance and reliability, characterized by higher glass transition temperatures than FR-4(Frame Retardant Type 4 of ANSI flame-retardant standard) material.
About OKI Electric Industry (OKI)
Founded in 1881, OKI Electric Industry is Japan's leading telecommunications manufacturer in the Info-telecom field. Headquartered in Tokyo, Japan, OKI provides top-quality products, technologies, and solutions to customers through its info-telecom systems and printer operations. Its various business divisions function synergistically to bring to market exciting new products and technologies that meet a wide range of customer needs in various sectors. Visit OKI's global website at http://www.oki.com/.
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Public Relations Division