Can anyone explain - about bondwire..

Hi, I was asked one question, which I could not answer correctly...(I don't know the answer, but I know I was wrong.. -.-

What is the skin effect and mutual inductance relationship?

For example, there are 4 bondwires..
If I connect them in parallel, then the total impedance goes down.
At high frequency, how does skin effect play and how does that affect on mutual inductance on bondwire?
(I know at high frequency, currents tend to flow on the surface due to electromagnetic field)

I am not very sure why a bondwire has inductance.
I thought the reason that a bondwire has inductance is "wire". (every length wire should have inductance) However, I believe there is more to it. The inductance occurs due to mutual inductance. Some folks talk about the inductance occurs because a bondwire form current circulation....

Anyway...can anyone expalin clearly?

Thank you in advance

Any time you have wires that are very close together, they wil have mutual inductance (they will "talk" to each other). I believe the point in using 4 bond wires is that they will all talk to each other if they are very close in the IC package, and this creates a boosting effect on their total inductance. Current will flow through all of them in the same direction (because they are wired in parallel according to your description) ==> This current will create a circular magnetic field surrounding each bond wire down its length ==> This magnetic field decreases in intensity as you go further away from the wire, but if the bond wires are very close, the magnetic field is still relatively strong ==> The magnetic field surrounding one wire strays into the next adjacent wire.

See this reference for a simple description of mutual inductance:
http://www.jwmiller.com/releases/Chow_Formatted_Reference_for_PCIM.pdf
Remember that all the L's in the equation are the bond wire self inductances.

You will find that at RF frequencies, sometimes you don't even need to lay out an inductor as a load for your amplifier. The bond wires themselves have enough inductance to accomplish the task.

woundwire you mean

is a power resistance made with a wire around a nono conductive core, yea it is similar a coil a very low inductance.

Added after 7 minutes:

Skin efect refers to distribution in the cross section of a wire for a DC it is equal in the whole section.

but with increaase of frecuency, charge carriers begins to leave the center, at high frequencies charge carrier are in the shores of the conductor like a orange peel.