Only bit by bit, all well, be possible to fundamentally solve the problem. 
The following may cause a few raised within the short main reasons: 
1. Short circuit between the inner layer circuit board itself; 
2. Dislocation of the inner plate layer; 
3. Inner conductive sheet laminated debris; 
4. Inner layer board design is not enough space emptied heart PAD; 
5. Drilling deviation; 
6. Desmear over; 
Generally the case, did not expect the place please friends add corrected later

Make multilayer, a few special attention: 
1: is to look at its side holes, as do the inner one, but the overall bias will be scrapped 
2: is your work environment is certainly better than 5s must be in place 
3: you must engage in the exposure machine clean, pay attention to members of the moves the exposure norms 
4: If there Qc, then you must look carefully,