Thermal Relief BGA pad design traces

Is there some good resources (.pdfs, websites, articles) that someone can point me to regarding design for bga footprints? I need to brush up on thermal relief design for bga footprints. I got a customer whose bga lands are masking defined on top of a large copper surface. There is no thermal relief for the pad from the large ground area since there is no trace connected to the pad. No what I mean? So... I need to find some guidelines on how to design bga lands that incorprate thermal relief for achieving uniform reflow etc... Thanks! B

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