Michael, I have found that getting a straight, definitive answer to questions like yours is almost impossible. I went through the same exercise trying to get the definition of a micro via. After doing extensive research and talking to a lot of PCB fabricators, I came up with the following: 1. Any via with a hole < .008" 2. Any via with a hole < .006" 3. Any via with a hole too small to be mechanically drilled, usually blind. Since it appears to be a moving target, I settled on number 3. The closest answer to your question that I've seen was found on the Resource Center section of the Merix Web site, http://www.merix.com. Specifically, at http://www.merix.com/resourcecntr/papers/highasp.pdf, a high aspect ratio is defined as: * Typical HAR criteria 7:1 o Example: 125 mil thick board w/ 18 mil drill * Aspect Ratio does not tell the whole story! o Example: 56 mil board w/ 8 mil drill o HAR definition expanded to include: * All small holes 13.5 mil or less * All boards over 93 mil Best regards, Ray Humphrey Senior PCB Designer Maxim Integrated Products -----Original Message----- From: TechNet [mailto:[log in to unmask]]On Behalf Of Michael Simms Sent: Tuesday, April 03, 2001 6:34 AM To: [log in to unmask] Subject: [TN] Low Aspect Via definition Hello T'Netters, I've not received a single reply from the last posting of this question, so I'd like to repeat: What document defines a low aspect via? Is there a numerical cut-off between a low aspect via and other vias? Certainly, in the 6012A document, acceptable minimum average copper thickness and absolute minimum copper thickness are defined for typical vias and low aspect vias. Is 3:1 a low aspect via? How about 4:1? Or 5:1? Any help out there? Mike Simms Trace Laboratories - Central ---------------------------------------------------------------------------- ----- Technet Mail List provided as a free service by IPC using LISTSERV 1.8d To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt delivery of Technet send the following message: SET Technet NOMAIL Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ---------------------------------------------------------------------------- ----- --------------------------------------------------------------------------------- Technet Mail List provided as a free service by IPC using LISTSERV 1.8d To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt delivery of Technet send the following message: SET Technet NOMAIL Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ---------------------------------------------------------------------------------