@Tim Edwards what is the top metalisation composition of the chips pads, is it Au?

No, it's all aluminum, as shown in the metal stackup diagram.

Can efabless help to put solder bumps on the aluminium pads ? I need for flip chip applications

No, we do not do that kind of service. For MPW-1 (and, I think, MPW-2), we outsourced the bump bonding to Micross (where it was done on a full wafer). I do not think it is possible to put solder bumps on a wirebond pad; they are not designed for it. The Micross process involved multiple layers of polyimide and copper prior to adding the bump bonds.

How can I go about it then? Any suggestion pls

I suggest that if you have a chip that is designed with wirebond pads, then you wirebond it.

I am planning for my September tapeout, so I can chnage still if there is a way

Is there are reason that you must have bump bonds?

I am doing flipchip of caraval with other chip, so vendor needs bumps, solder bumps r must for it

Then you would need to find a 3rd party vendor to add the solder bumps. I do not know of any that do solder bumping on a single die, just whole wafers.

I will look for solutions accordingly. Thanks for feedback 😊

Samarth, It is both common and feasible to bond between die (Or you have a tall stack of multiple die where you must bump them.) This service can be done on individual die during assembly and does not require any wafer level processing. This is a well proven technology offered by many vendors. Google "stacked wirebonde dice" images https://ewh.ieee.org/soc/cpmt/presentations/cpmt0210b.pdf