andyk, These are very common questions that come up with blind vias. I'd like to try to answer them from our perspective: a) Certainly, controlled depth blinds are less costly to process and therefore will be a lower price to you. b) Repeatability of depth should not be a real mystery to your supplier. Most drilling equipment configured for depth control utilizies a Z-axis encoder that is triggered by surface contact of the pressure foot. So long as the laminate thickness and surface topography is kepth under control, there should be repeatability in depth within a reasonable tolerance window (.003" is not uncommon). c) I don't have any data to support long term reliability for these holes, but aboviously, very many suppliers are making blind vias in this fashion, and have been for a number of years. The key issue surrounds the ability to properly prepare and metalize the holes, which leads to... d) The upper limit on aspect ratio for CDBV's, generally in the industry, seems to be around 1:1. The obvious problem here is solution movement during metalization. Hole size also plays a big role in this. Just because a shop can do 1:1 with a .015" drill doesn't mean they are capable of 1:1 with a .010" drill. Each shop is a little different. Hope this helps. Andy Slade HADCO Tech Center One 7 Manor Pkwy Salem, NH 03079 (603)-896-2210 ------------------------------------------------------------------ Hi, I'n in the end run of a revision to a board design which is double sided eight layers with blind vias on layers 1/2, 1/4, 5/8 and 7/8, as well as the normal through-hole 1/8 vias. Sizes are 0.3mm (12mil) for in-pad blind vias and 0.6mm (24mil) wherever I can get away with it. We've already had batches of Rev A boards made up with sequential lamination and with controlled depth drilling and we're in the process of evaluating suppliers and their boards. My problem is that we are having trouble nailing down any sort of specification for our next run. These will also be prototypes but we're getting close to volume production and need something for QA to hang its hat on for incoming inspection. Factors we are considering are: a) Boards manufactured with controlled depth drilling promise to be considerably less expensive (30% on one estimate) b) The repeatability of the depth of drilling is an unknown, from stack to stack and from batch to batch. c) The long term reliability of a blind via defined this way is unknown to us d) The aspect ratio of a blind hole appears to be critical, but what is optimum and what is acceptable? and so on and on. Can anyone help? Thanks in advance *************************************************************************** * 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. * ***************************************************************************