Cameron - Things you need to know going in to a controlled impedance circuit board include: 1.) The effective frequency of the signals to be impedance matched. Don't try control impedance on a global basis the head and heart aches aren't worth it. The effective frequency can be calculated as F in Hz =0.35/Signal rise time in nsec. 2.) The target impedance for the lines in question. For FR4 the practical range is around 30-100 ohms anything outside that range will require a material change. 3.) The relative Permittivity(sp?) of the substrate being used. For FR4 it will be between 3.8 and 4.5 depending on Frequency. 4.) Layer stack-up. This is critical in controlled impedance. 5.) Critical Length for the controlled impedance lines. Calculate as Critical Length in inches = [(Trise * Speed of light(inches/sec))/sqrt (Er)]/2. Don't be surprised, however if the engineer gets a puzzled look when you ask for the rise time, and is a long time getting back to you with it. This is where the real fun of PCB design starts >:-> Jeffrey A. McGlaughlin Printed Circuit Board Designer Battelle Memorial Institute Columbus Ohio -----Original Message----- From: [log in to unmask] [SMTP:[log in to unmask]] Sent: Thursday, August 20, 1998 10:35 AM To: [log in to unmask] Subject: [TN] More Controlled Impedance Thanks to those who responded to my previous question about trying to find some information about how to design a board with controlled impedance. Unfortuneatly, I still haven't been able to find any information on the topic. I now have an engineer who wants me to design his board with some controlled impedance. Can anyone tell me what questions I should ask him, and give me some design considerations that I should pay attention to. Thanks, Cameron ################################################################ TechNet E-Mail Forum provided as a free service by IPC using LISTSERV 1.8c ################################################################ To subscribe/unsubscribe, send a message to [log in to unmask] <mailto:[log in to unmask]> with following text in the body: To subscribe: SUBSCRIBE TechNet <your full name> To unsubscribe: SIGNOFF TechNet ################################################################ Please visit IPC's web site (http://www.ipc.org <http://www.ipc.org> ) "On-Line Services" section for additional information. For technical support contact Hugo Scaramuzza at [log in to unmask] <mailto:[log in to unmask]> or 847-509-9700 ext.312 ################################################################ ################################################################ TechNet E-Mail Forum provided as a free service by IPC using LISTSERV 1.8c ################################################################ To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body: To subscribe: SUBSCRIBE TechNet <your full name> To unsubscribe: SIGNOFF TechNet ################################################################ Please visit IPC's web site (http://www.ipc.org) "On-Line Services" section for additional information. For technical support contact Hugo Scaramuzza at [log in to unmask] or 847-509-9700 ext.312 ################################################################ ################################################################ TechNet E-Mail Forum provided as a free service by IPC using LISTSERV 1.8c ################################################################ To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body: To subscribe: SUBSCRIBE TechNet <your full name> To unsubscribe: SIGNOFF TechNet ################################################################ Please visit IPC's web site (http://www.ipc.org) "On-Line Services" section for additional information. For technical support contact Hugo Scaramuzza at [log in to unmask] or 847-509-9700 ext.312 ################################################################