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HIGH SPEED, HIGH DENSITY POLYIMIDE SPACE TRANSFORMER WITH GHz BANDWIDTH

IP.com Disclosure Number: IPCOM000039544D
Original Publication Date: 1987-Jun-01
Included in the Prior Art Database: 2005-Feb-01
Document File: 3 page(s) / 55K

Publishing Venue

IBM

Related People

Scheuermann, M: AUTHOR

Abstract

There is a need for a high speed space transformer with fast risetimes and high density (10-mil center-to-center) spacing. Two different types of space transformers are known, the first being a hybrid coax (HYCO) space transformer and the second being a multilayer ceramic (MLC) space transformer. The fabrication of the HYCO is extremely labor intensive with very little chance of being automated. On the other hand, the fabrication of the MLC space transformer is highly integrated; however, it is fairly expensive and has a long development and lead time. Both of these space transformers contact the chip under test (CUT) using an interposer which is placed between the chip and the space transformer. The pins on the interposer are unshielded and have high inductance.

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HIGH SPEED, HIGH DENSITY POLYIMIDE SPACE TRANSFORMER WITH GHz BANDWIDTH

There is a need for a high speed space transformer with fast risetimes and high density (10-mil center-to-center) spacing. Two different types of space transformers are known, the first being a hybrid coax (HYCO) space transformer and the second being a multilayer ceramic (MLC) space transformer. The fabrication of the HYCO is extremely labor intensive with very little chance of being automated. On the other hand, the fabrication of the MLC space transformer is highly integrated; however, it is fairly expensive and has a long development and lead time. Both of these space transformers contact the chip under test (CUT) using an interposer which is placed between the chip and the space transformer. The pins on the interposer are unshielded and have high inductance. These features degrade the high speed characteristics of the space transformer. At high frequencies probe needles as short as 30 mils can radiate, causing excessive degradation and crosstalk. Thus, it is important to shield the signal lines as far as possible to the CUT. Furthermore, the power supply lines must provide enough bypass capacitance as close as possible to the CUT. This article describes a space transformer which addresses the above problems. The space transformer is assembled using sheets of microstriplines similar to those used in the Josephson sample holders. These linear arrays of microstriplines use a copper ground plane, polyimide insulation, and copper striplines (Fig. 1). These striplines have nominal impedance of 50 (+/-) 2.5 ohms. A signal having a 200 psec risetime was degraded to 400 psec after propagation through 1.4 meters of cable. On the driver end the striplines were terminated directly to SMA connectors. To fabricate the space transformer; cables of these microstriplines would be laminated together at one end to form a dense two-dimensional array of I/O's which would be connected to the CUT. The structure is shown schematically in Fig. 2. The geometry of the structure must be changed slightly in order to maintain an impedance of 50 ohms. The other ends of the cables are kept free so each microstripline can be connected directly to an SMA connector just as the Josephson cable was. Each cable of microstriplines as well as e...