Question: We have a situation where we have gold boards which accept gold wire bonding, but are failing a pull test. Other than making sure the boards are clean with a quick trip into the degreaser, is there any other way to refresh gold plating to help these boards pass pull testing?
Answer: I’m not quite sure how to answer this question as it does not state how the joint failed. Did the wire pull off the gold plating? Did the wire break at the weld? Did the plating come off the board?
We need to define what kind of gold plating is on the board. Is it Electroplated Gold? Is it ENIG? Does it have a Nickel underplate? How thick is the gold plating?
I’ve checked Mil-Std-883F method 2011.7 Bond Strength (Destructive Bond Pull Test) and they have a long list of defects which I’ve attached along with the table of minimum bond strength.
3.2.1 Failure category. Failure categories are as follows: When specified, the stress required to achieve separation and the category of separation or failure shall be recorded.
a. For internal wire bonds:
(a-1) Wire break at neckdown point (reduction of cross section due to bonding process).
(a-2) Wire break at point other than neckdown.
(a-3) Failure in bond (interface between wire and metallization) at die.
(a-4) Failure in bond (interface between wire and metallization) at substrate, package post, or other than die.
(a-5) Lifted metallization from die.
(a-6) Lifted metallization from substrate or package post.
(a-7) Fracture of die.
(a-8) Fracture of substrate.
b. For external bonds connecting device to wiring board or substrate:
(b-1) Lead or terminal break at deformation point (weld affected region).
(b-2) Lead or terminal break at point not affected by bonding process.
(b-3) Failure in bond interface (in solder or at point of weld interface between lead or terminal and the board or
substrate conductor to which the bond was made).
(b-4) Conductor lifted from board or substrate.
(b-5) Fracture within board or substrate.
c. For flip-chip configurations:
(c-1) Failure in the bond material or pedestal, if applicable.
(c-2) Fracture of die (or carrier) or substrate (removal of portion of die or substrate immediately under the bond).
(c-3) Lifted metallization (separation of metallization or bonding pedestal from die (or carrier) or substrate.
d. For beam lead devices:
(d-1) Silicon broken.
(d-2) Beam lifting on silicon.
(d-3) Beam broken at bond.
(d-4) Beam broken at edge of silicon.
(d-5) Beam broken between bond and edge of silicon.
(d-6) Bond lifted.
(d-7) Lifted metallization (separation of metallization) from die, separation of bonding pad.
(d-8) Lifted metallization.
I’m not sure how to refresh the gold plating, from my perspective it is either good or it isn’t and this is based upon the type of gold plating that is on the board.
I wish I had a better answer for you, but more information and lab work is needed to provide an answer to the question as to why are the bonds failing.