Giga Connections, inc. - DC-40Ghz Design Verification Socket

Giga Connections, inc. integrates a Conductive Diamond Plated (CDP) Interposer with a new one-screw heat sink/fan test socket assembly to create a new line of low cost and easy-to-assemble BGA test sockets with interconnect bandwidths beyond 40 GHz.

Each of our Custom Design Verification socket is fully tested before it is shipped to our customers.  A test board is built and a shorting die is inserted to validate all of pads are connected to the die. The slide show visually describes how the socket is assembled for testing.

Current Path Through the GCI Dual Pin-less Kapton Interposer with Gold Plated Diamond Pads

The “Side” view picture on the right show a cutout of two interposers one atop another. The round object on top represent a BGA solder ball pressing down on the conductive diamond pads that match the package layout. Each pad is plated with conductive diamonds that form a sharp multi-point non scrubbing compression surface that breaks through any oxide or contaminate on the solder ball forming a “solder like” connection.

Each pad matches the size and pitch of the device package to reduce impedance discontinues. There is a small cantilever trace (=>20 mills) that connects the top pad to a bottom pad on the top cantilever. The bottom interposer is the same at the top interposer but flipped and makes contact to return the signal via its cantilever trace back to the same position under the solder ball. The signal path is traced out by a green line in the diagram.  

The “Top” view picture on the left is a picture of the conductive diamond pads and the green trace is the cantilever trace, connecting the tip pad to the bottom pad on each interposer.  To provide independent movement for each pad, the pad and cantilever trace is cut out using a patent pending laser technique. Separating each pad and cantilever section from the kapton provides independent movement for each pad. This technique provides a pin-less mechanical compliant electrical connection for each solder ball on the device and its associated pad on the test board.  

The TDR impedance profiles in the figures above show a communication channel using the Conductive Diamond Plated Interposer socket compared to a channel using a pogo pin socket. The Z-Line impedance waveform from the TDR was measured into the pogo pin socket. It can be seen that the pogo pin socket  presents a large capacitive impedance discontinuity ~38 ohms verses only 1.6 ohms for the Conductive Diamond Interposer Socket from Giga Connections, Inc.  The large capacitance discontinuity of the pogo pin socket reduces the S11 S-parameters of the test board and therefore can not be used to judge the actual signal integrity performance of the device.  The Conductive Diamond Interposer socket impedance therefore, compares to that of a soldered device. This socket can be used for full SI testing, without soldering the device to the test board, enabling the test board and device can be reused saving both money and time.

Eye Diagram measurement using the Conductive Diamond Socket

6.25 Gb/s, NRZ Eye Diagram

An NRZ eye diagram was measured at a raw data rate of 6.25 Gb/s. The TX amplitude is set to 0. The TX EQ taps are set to [0 80 -15 0 0]. No codec is used (pure PRBS 231-1). The onboard PLL is used as the serial link reference clock to the EN6110.

10 Gb/s, PAM4 Eye Diagram

 A PAM4 eye diagram was measured at a raw data rate of 10 Gb/s. The TX amplitude is set to 0. The TX EQ taps are set to [0 80 -10 0 0]. The 16b10s Codec is used. The onboard PLL is used as the serial link reference clock to the EN6110.

TDR Repeatability

The repeatability of the socket TDR impedance profile was tested by removing the socket from the U2 position, and then reinstalling it using the same torque value. TDR measurements and Z-Line extractions were performed each time. The above TDR plot shows a comparison between the Z-Line TDR data of the two installations of the socket. The region of the impedance traces between the EN6110 balls and the EN6110 RX termination shows about 1 – 2 ohms of impedance difference. This is a very minimum impedance difference, and demonstrates that the socket has a high level of repeatability.