Richard, -perhaps you could elaborate further - are you sure you mean a ring void? or are you seeing a barrel crack in the center of the hole? Is there anything else "unusual" about the plated barrel of the hole - is the copper thin in the problem area, etc.? How about on the surface of the part - are the pads lifting? Usually the greatest stress is near the surface of the part, and you might expect to see some innerconnect problems or cracks in the plated copper at the knees of the holes if you have a lot of Z-axis expansion trouble from undercured or low Tg material. It's pretty unusual for a copper bath to be so screwed up that the ductility goes completely away (leading to barrel cracks), but it does happen - but frequently the knees crack first (unless the plating is thin in the center of the hole, i.e. dogboning). Speaking as a fabricator, I don't know why you'd put thermals on some planes and not on others; maybe you can explain why! Regards, Fred J. >>> Richard G Smith <[log in to unmask]> 02/24/98 05:13pm >>> Fellow Techies, I need your help!! Here's the situation. We have an eight layer PCB with four internal planes. Layers 3 and 4 of the planes have thermally relieved vias, layers 5 and 6 do not. The via size is .018 +.000 -.018 finished and are tented with soldermask. The problem is that ring voids occur sporadiclly on layers 5 and 6 (non-thermal ties) after multiple thermal excursions during assembly. A microsection of the board has confirmed this. I contend that the board was fabricated improperly using lower grade FR-4 and in conjunction with other issues such as low ductility copper and no thermal ties caused this problem. I am a PCB Designer so I may be biased. The assembler is saying that this is purely a design issue based upon the fact that no thermal ties were provided. In all my resarch no one (including fab houses) has indicated that this problem is related to the lack of a thermal. Any insight would be greatly appreciated. Rick ################################################################ TechNet 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 TechNet <your full name> To unsubscribe: SIGNOFF TechNet ################################################################ Please visit IPC web site (http://jefry.ipc.org/forum.htm) for additional information. For the technical support contact Dmitriy Sklyar at [log in to unmask] or 847-509-9700 ext.311 ################################################################ ################################################################ TechNet 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 TechNet <your full name> To unsubscribe: SIGNOFF TechNet ################################################################ Please visit IPC web site (http://jefry.ipc.org/forum.htm) for additional information. For the technical support contact Dmitriy Sklyar at [log in to unmask] or 847-509-9700 ext.311 ################################################################