This is how we do most of our VNA measurements, including 4-port mixed-mode. Wafer probes (we now usually call them microprobes), are now available in many different styles that are well-suited for PCB applications. These include different access angles and lengths (to allow probing on populated boards), as well as Ground-Signal separation (pitch). The largest standard pitch that you will be able to purchase is in the neighborhood of 1250u (about 50 mils). Although you can order probes in a wider pitch, your frequency range will limit the probe pitch that you can use. For calibrating with a 2-port VNA, using the Short, Open, Load and Thru (SOLT) technique to 15-20 GHz, we normally use probes that have a maximum pitch of around 650u to 1000u. A wide range, yes, but the ability to calibrate accurately is dependent on many factors including operator skill, condition of the probes and cal substrate as well as the instrument accuracy (including cables and adapters). We often must measure boards that have not been designed for these kinds of probe-based measurements, and frequently have to "modify" the boards to accommodate the probes. This sometimes involves soldering copper tape to boards, "painting" with silver-filled epoxy or drilling down to a ground plane. Imagination is required. Of course, this kind of "test tooling" will modify the interconnect measurement, and must be taken into account when evaluating the data. De-embedding the added launch parasitics at 20 GHz will almost certainly be necessary. However, we long ago concluded that the accuracy and flexibility of the probe-based measurement system is worth the additional work for these high frequency PCB measurements. Our PCB Probe Station was created to meet this kind of VNA measurement requirement. You can learn more about it on our website, at www.gigatest.com Good Luck. -- Gary Otonari GigaTest Labs ------------------------------------------------------------------------ ------------ Attend the GTL Signal Integrity University in Sunnyvale, CA - November 8-16 GTL 122 - Fundamental Principles of Signal Integrity GTL 250 - High Speed Board Design GigaTest Labs 134 South Wolfe Road * Sunnyvale, CA * 94086 408.524.2700 www.gigatest.com -----Original Message----- From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf Of pritchard, jason Sent: Tuesday, October 19, 2004 8:37 AM To: si-list@xxxxxxxxxxxxx Subject: [SI-LIST] VNA Probing Solution Hi All, I am looking for a probing solution to take s-parameter measurements out to 10-15Ghz. These measurements are on boards that are currently developed and don't have anyway of connecting an SMA to the board. I've looked at wafer probe manufacturers offerings and they seem to be accurate to at least 20Ghz depending on grounding configuration and probe style. The pitfalls are that the probes are pitch specific and too fragile to probe by hand. They also are fairly expensive. My connections vary from board to board. The ground connections points can very signifigantly in distance. Signal pitch can be 1mm under an ASIC to 2mm apart at a connector or board via. Currently I use an sma connected to a semi-rigid coax with a wire from the ground shield to my ground point on the board. This method seems to be accurate to 3 or 4 Ghz if I get a close ground. It's my understanding that I can only get accurate measurements if I get the ground as close as 1/50th of my maximum frequency. Is this too conservative? Does anyone have any better Ideas on how I can probe boards and get good results out to 10Ghz? Is this even possible? Thanks, Jason Pritchard ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List FAQ wiki page is located at: http://si-list.org/wiki/wiki.pl?Si-List_FAQ List technical documents are available at: http://www.si-list.org List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List FAQ wiki page is located at: http://si-list.org/wiki/wiki.pl?Si-List_FAQ List technical documents are available at: http://www.si-list.org List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu