For small blind via, an aspect ratio of 0.5-1 (depth/diameter) is good. We typically recommend .005"-.006" (drill, not finished) hole diameter for laser drilling. I believe this is also a good number for other technologies, such as plasma and photoimageable dielectric. For large, deep blind vias (typically go down several layers), sequential lamination might be necessary. This means you build a multilayer subassembly, drilled, plated and then laminated with another subassembly. In this case, the aspect ratio limitation of the "finished blind via" should be the same as the through vias. I think I may have repeated Dougal's comments. If so, please take it as a confirmation. Mason Hu Zycon Corporation ______________________________ Reply Separator _________________________________ Subject: FAB: BLIND VIAS Author: [log in to unmask] at corp Date: 11/7/96 4:43 AM Jim Marsico wrote: Can anyone tell me the standard aspect ratio for blind vias? What is the minimum and maximum hole diameters? I think that I can only answer from experience rather than any design guidelines. We manufacture sequentially bonded blind vias with hole diameters of 0.3mm in 007" laminate, 0.35mm in 028" laminate, and 0.6mm in 070" laminate, as well as lots of others in between. The aspect ratio on sequentially bonded (resin filled) blind vias is not as important as the length of the hole. We are aware of issues with long holes due to the resin expansion during SMD assembly, and it can be predicted that the maximum hole depth should be 0.6mm (024") to avoid this issue. I am currently evaluating the reliability of different aspect ratio blind vias, in different thicknesses and types of material with different plating thicknesses, and hopefully will be able to publish a paper in the new year. As far as depth drilled blind vias (access blind via holes), the hole size is determined by the technique used (mechanical/laser etc) but the rule of thumb is to keep the aspect ratio to 1 or less. Dougal Stewart Exacta Circuits Scotland *************************************************************************** * TechNet mail list is provided as a service by IPC using SmartList v3.05 * *************************************************************************** * To unsubscribe from this list at any time, send a message to: * * [log in to unmask] with <subject: unsubscribe> and no text. * *************************************************************************** *************************************************************************** * TechNet mail list is provided as a service by IPC using SmartList v3.05 * *************************************************************************** * To unsubscribe from this list at any time, send a message to: * * [log in to unmask] with <subject: unsubscribe> and no text. * ***************************************************************************