In ATE Loadboard design ,with Serdes’s speed getting higher and the DUT BGA’s pitch getting smaller,the fabrication risk is getting higher, and the tight SI spec is getting harder to meet.In each time, we have to try many solutions and do 3D simulation to each of them,then find out a solution with good SI performance and low fab risk. As 3D simulation is time consuming, our project schedule cannot allow us spend too much time to make experiment. Now,With the help of Clarity 3D layout ,its embedded Clarity 3D and Hybrid solver makes it possible.In this paper, firstly, two traditional solutions has been introduced:1.PTH via backdrill solution can be used when DUT BGA is 0.8mm pitch or larger,it can easily pass the simulation spec;but this solution is not suitable for DUT pitch with 0.5mm or smaller, as return loss is too bad. 2. Blind via solution can get good simulation result as blind via is no stub,but,it will lead to high board fabrication risk and low yield.To overcome this dilemma,a new solution combing the advantage of these two solution is proposed, it is laservia+PTH backdrill solution.With the help of laservia, it allow us to route the loopback in outer ring of BGA in 1 layer,so that to other loopback in inner ring, we can easily do fanout use PTH via,and then backdrill the long stub.As in order to keep good contact of DUT socket pin, DUT fanout vias should be filled with epoxy,in this paper, the SI effect of air over stub and epoxy over stub after backdrill is also discussed.It is verified that air over stub hardly leaks the energy away, it will have better insertion and return loss, which means we should apply epoxy filling first, back-drill last.The final result shows we get good SI performance and good fabrication yield,and simulation efficiency can be improved by 20%.