Hi John-Sorry for the delayed response. I may not be the best one to answer this question, but I'll give it a shot. When talking about multilayer PCB's, a through hole is one that goes through all layers, and a blind hole is one that is only present on some of the layers. We're not talking about a hole that is used to mount a component. A blind hole is going to be used as a "via" which allows a trace to have connectivity to another layer. The inside surface of the hole will be plated, so it connects traces on two or more layers together. All of the PCB's I have designed so far are two layer, so I've never used a blind hole. You'll only see blind holes on boards of more than two layers, and most often on boards that are really crowded.As far as how it affects the signal- I think there would be very little, if any, measurable difference between signals routed on traces with through holes versus blind holes. Other factors like capacitance between traces would have more of an impact.If I have misunderstood your question, please let me know. You folks who have done a lot of work on multilayer PCB's, please chime in here.-Rick
