Sorry I didn't read this one before replying earlier. It's unlikely that the dielectric constant of the mask changed that much, however the thickness may have. A cross-section will tell you for sure. Timothy Reeves ECD Circuit Board Division 13626 South Freeman Road Mulino, OR 97042 [log in to unmask] (503) 829-9108 (800) 228-8198 FAX (503) 829-5482 > ---------- > From: Tuan Le > Sent: Thursday, February 17, 2000 13:16 > Subject: Re: Soldermask effect on impedance > > Thank you for your response, Mike. However, I guess I wasn't clear on my > question: I didn't expect the impedance to drop that much after > soldermask. Usually I see 2 to 3 ohms the most. > > Tuan > > -----Original Message----- > From: Beckman, Michael W [ mailto:[log in to unmask]] > Sent: Thursday, February 17, 2000 11:54 AM > To: 'TechNet E-Mail Forum.'; 'Tuan Le' > Subject: RE: [TN] Soldermask effect on impedance > > > Hi Tuan, > Just real briefly; Zo is = to L/C (inductance over capacitance) and > capacitance is proportional to Er (dielectric constant), so C= Er A/d > (area) > over d (distance/separation). > It is important to understand that solder resist is a dielectric and acts > as > insulation to the surface traces, thus reducing the circulating currents. > I hope this helps. > > > > Mike Beckman > > > [log in to unmask] > > Packaging Engineer > Assembly Technology Division > CH5-157 Ofc. (602) 554-4232 > 5000 W. Chandler Blvd. Fax (602) 554-7615 > Chandler, Arizona 85226 Pgr. (602) 340-3983 > > > > > -----Original Message----- > From: Tuan Le [ mailto:[log in to unmask]] > Sent: Thursday, February 17, 2000 12:13 PM > To: [log in to unmask] > Subject: [TN] Soldermask effect on impedance > > > > Hi everyone, > > I have done some tests recently by measuring impedance (on traces from the > > coupons) before and after soldermask. I found that there are quite a > large > drop in impedance after soldermask: 4 to 6 ohms for single ended and 8 to > 10 > ohms for differential impedance. Has anyone experienced this? Could > anyone > offer me an explanation of what happened? We use the same Taiyo product > for > a long while. > > Your help is greatly appreciated. > > Tuan Le > [log in to unmask] > > ############################################################## TechNet Mail List 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 web site (http://www.ipc.org/html/forum.htm) for additional information. If you need assistance - contact Gayatri Sardeshpande at [log in to unmask] or 847-509-9700 ext.5365 ##############################################################