hi its hard to say this way (without adequate caps/ stitching vias), but i think you should make shure that you have VCC1-GND decoupling capacitors close to both the driving IC and the signal-via-transition (layer1-to-layer-5). Then it would go this way: from IC gnd-pin, to gnd plane, through the vdd1-gnd decap to vdd1 plane, through the vdd1 plane following the signal, through the vdd-via of the vdd1-gnd decap at the signalvia, through the decap itself, through the gnd-via of the decap, to both gnd planes, then following the signal in both gnd planes. vdd2-gnd decap is not even involved, i think. Or route primarily on layer 5 or 4 and dont change layer. regards, Istvan Nagy Concurrent Tech. plc, UK ----- Original Message ----- From: <jhasson@xxxxxxxxxxxxxxxxxxx> To: <si-list@xxxxxxxxxxxxx> Sent: Thursday, June 11, 2009 4:31 PM Subject: [SI-LIST] Return current and stack up > Hi, > Asumming I have the following 8 layer stack up : > Layer 1 - - - - - - - Sig > Layer 2 - - - - - - - VCC1,VCC3 > Layer 3 - - - - - - - GND > Layer 4 - - - - - - - Sig H > Layer 5 - - - - - - - Sig V > Layer 6 - - - - - - - GND > Layer 7 - - - - - - - VCC2,VCC4 > Layer 8 - - - - - - - Sig > > What would be the return path of a signal going from layer 1 (for 2 inches > running above VCC1 for instance) to layer 5 (for 4 inches) driven by a > component powered by VCC2 if the component is set up above layer 1 and > driving high ? Would it be going through decoupling capacitors of VCC2 to > decoupling capacitors of VCC1 to then get to the layer 6 reference plane ? > > Best regards, > > JF Hasson > > ------------------------------------------------------------------ > To unsubscribe from si-list: > si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field > > or to administer your membership from a web page, go to: > //www.freelists.org/webpage/si-list > > For help: > si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field > > > List technical documents are available at: > http://www.si-list.net > > List archives are viewable at: > //www.freelists.org/archives/si-list > or at our remote archives: > http://groups.yahoo.com/group/si-list/messages > Old (prior to June 6, 2001) list archives are viewable at: > http://www.qsl.net/wb6tpu > > > ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List technical documents are available at: http://www.si-list.net List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu