From IPC-2221: 9.2.7 Blind and Buried Vias - Plated-through holes connecting two or more conductive layers of multilayer printed board, but not extending fully through all layers of the base material comprising the board, are called Blind and Buried Vias. 9.2.7.1 Blind Vias - Blind via plated-through holes extend from the surface and connect the surface layer with one or more internal layers. The blind via can be produced by two methods: (1) After multilayer lamination by drilling a hole from the surface to the internal layers desired and electrically interconnecting them by plating the blind via holes during the plating process; (2) Before multilayer lamination by drilling the blind via holes from the surface layers to the first or last buried layers and plating them through, imaging and etching the internal sides, and then laminating them in the multilayer bonding process. For the second process if an interconnection is desired between the surface layer and more than one internal layer, sequential etching, laminating, drilling and plating-through of these layers together before final multilayer lamination is required. Blind via holes should be filled or plugged with a polymer or solder resist to prevent solder form entering them as solder in the small holes decreases reliability. 9.2.7.2 Buried Vias - Buried via plated-through holes do not extend to the surface but interconnect only internal layers. Most commonly the interconnection is between two adjacent internal layers. These are produced by drilling the thin laminate material, plating the holes through and then etching the internal layer pattern on the layers prior to multilayer lamination. Buried vias between non-adjacent layers requires sequential etching of inside layers, laminating them together, drilling the laminated panel, plating the holes through, etching external sides and laminating this panel into the final multilayer panel. 9.2.7.3 Hole Size of Blind and Buried Vias - Small holes are usually used for either blind or buried vias and may be produced mechanically, by laser or by plasma techniques. The minimum drilled hole size for buried vias is shown in Table 9-4 and the minimum drilled hole size for blind vias is shown in Table 9-5. In either case plating aspect ratios must be considered; small deep blind vias are very difficult to plate because of decreased throwing-power and limited plating solution exchange in the holes. Blind and buried via holes may be plated shut; thus, the master drawing call out should be similar to that used for through-holes vias. See sectional standards for more information. Table 9-4 Minimum Drilled Hole Size for Buried Vias Layer Thickness Class 1 Class 2 Class 3 <0.25 mm 0.10 mm 0.10 mm 0.15 mm 0.25 - 0.5 mm 0.15 mm 0.15 mm 0.20 mm >0.5 mm 0.15 mm 0.20 mm 0.25 mm Table 9-5 Minimum Drilled Hole Size for Blind Vias Layer Thickness Class 1 Class 2 Class 3 <0.10 mm 0.10 mm 0.10 mm 0.2 mm 0.10 - 0.25 mm 0.15 mm 0.20 mm 0.3 mm >0.25 mm 0.20 mm 0.30 mm 0.4 mm Lisa Williams Technical Project Manager IPC 2215 Sanders Road Nortbrook, IL 60062 www.ipc.org >>> Bock Ming Gai Joanne <[log in to unmask]> 10/16/98 01:29AM >>> Hi all, I'm currently looking into all the aspects of blind and buried via (Design constraints, manufacturing and the do & don't). Can anyone out there help me? Your help is very much appreciated. Joanne ################################################################ DesignerCouncil E-Mail Forum 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 DesignerCouncil <your full name> To unsubscribe: SIGNOFF DesignerCouncil ################################################################ Please visit IPC's web site (http://www.ipc.org) "On-Line Services" section for additional information. For technical support contact Hugo Scaramuzza at [log in to unmask] or 847-509-9700 ext.312 ################################################################ ################################################################ DesignerCouncil E-Mail Forum 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 DesignerCouncil <your full name> To unsubscribe: SIGNOFF DesignerCouncil ################################################################ Please visit IPC's web site (http://www.ipc.org) "On-Line Services" section for additional information. For technical support contact Hugo Scaramuzza at [log in to unmask] or 847-509-9700 ext.312 ################################################################