ADC! Seems like only yesterday. I'm currently designing and buying two MLB's with CSP/BGA's on 30 mil centers. The sixteen layer version, with differential broad side impedance requirements on specified digital layers, is about 120 mils thick with 10 mil interfacial vias - currently. It costs about 1500 dollars in 10 piece quantities for 5-7 day turn from a NATIONALLY RECOGNIZED board shop. No quotes on production quantities yet. It will cost about 300 dollars more for the micro via version with buried vias connecting the internally placed dogbones allowing pad only outers. The 22 layer version is priced at about the same ratio starting about 2000 dollars but must have the blind micro vias and buried vias as its thickness is about 180 mils. Simply, there is no choice. As these boards exceed my expetations for aspect ratio, partly considering the plating thickness issue of .8 mils minimum, it will be respun to include micro vias in the BGA pads, eliminating dogbones on the outers, and reducing the aspect ratios in that area as the bones will be interconnected on the inners using buried vias. Again, the cost of the new design will be about three hundred dolars more for the same turn times. However, it is expected to save much more as a more reliable product. As Werner said, who has the data concerning plating thickness reduction as it is now being practiced. However, with a Z axis expansion rate of about 50 ppm/degree C, and a ductility factor nearing 20%, with a 170 degree Tg material, the hole walls should stay together under thermal stress. We have similar designs for varying other layer counts. There seems to be about a 20%, or so, cost differential between the two choices, but the long term effects should offset the decision. Earl Moon --------------------------------------------------------------------------------- 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 ---------------------------------------------------------------------------------