I am currently getting involved in one PCB design which is associated with high-speed signal(40Gbps PAM4 signal).On the board,a chip which transmits and receives data is bonded and transfers data through the traces and connectors.
I know signal running at such speed is susceptible to skin effect,dielectric loss and reflections.I have also heard bond wire should be as short as possible to reduce its inductance,so I try to place those pads(also known as gold fingers) of high-speed signal really close to the chip(as 7,8,13,14,17,18,20 shown in 1).
My questions are:
(1)Is the length of bond wire shorter,the better?What is the theoretical basis?
(2)Can I pick up the best bonding wire length based on simulation result?What simulation tool should I use?(HFSS,ADS maybe?)
(3)In some article,bond wire is treated as transmission line.But isn't this too short to be modeled as?Is this a good approximation?
(4)Except from bond wire length,what are the design considerations of pad(gold finger) size?
Any insightful answer of any one of the questions will be appreciated,thanks!