Good Morning!
I'll throw a couple of ideas out that might be contributors to your
bonding problems:
#1- If I am reading your data correctly I don't see any nickel
underplate between the copper and the gold. Copper can diffuse through
gold at a very reasonable rate and once it reaches the surface will
interfere with your bonding. Most wirebonding applications I am
familiar with use a nickel underplate to enhance the bonding
characteristics (although I know of specific applications where people
don't have a nickel underplate - these are few and far between). Your
"orange stain" sounds like copper. Try conducting a SEM analysis of a
carefully prepared microsection.
#2 - Prior to the wirebonding operation, how is the surface cleaned?
You may have surface contamination that is causing problems - most
people either do ozone or plasma cleaning prior to wire bonding.
One good resource to look at is "Wire Bonding In Microelectronics" ,
ISBN 0-930815-25-4. Good Luck.
Dave Hillman
Rockwell Collins
[log in to unmask]
______________________________ Reply Separator _________________________________
Subject: FAB: organic contam. on wire-bond gold
Author: [log in to unmask] at ccmgw1
Date: 11/27/96 6:18 PM
HELP - What's the secret to making wire-bondable gold?
Our ppm failure rate on wire bond sites is a little too high for our
customer. Smallest wire-bond pad is about .014"x .050" and wire
mat'l is Al (generally higher failure rates on smaller pads). The
highest percentage culprit has been described as an [arguably]
visible "orange stain" - very thin with a Carbon/Oxygen signature.
Board is double-sided with the following route: Drill, panel plate
Cu, image & plate gold (DuPont 9020), strip resist (RR3), image
(cover gold), cupric etch circuitry, pumice w/brushes, LPISM
(Probimer-65), solvent develop, bake & UV cure, legend, ET, Entek 56.
Gold parameters: 83-85 knoop, Ni content: 30-40ppm, As,Cu,Pb,Co, all
less than 3 ppm, Gold conc. is on low side: Au strike: 0.15-0.25
tr.oz./gal, Au Plate: 0.4-0.6 tr.oz./gal @ ~2 ASF.
Questions:
- What are the most common contributors to wire-bond failures?
- Is LPISM residue one of them?
- Are aqueous developable LPISMs generally more successful?
- What are the, say, 3 most critical parameters to control at deep
gold?
- How critical is gold surface topography (roughness)?
- Are ET pin dents a failure cause?
- Can pumice operations be detrimental to the gold surface?
- Is low Au concentration necessarily a liability?
Any input will be greatly appreciated.
J.Felts
PC World, Toronto
***************************************************************************
* TechNet mail list is provided as a service by IPC using SmartList v3.05 *
***************************************************************************
* To unsubscribe from this list at any time, send a message to: *
* [log in to unmask] with <subject: unsubscribe> and no text. *
***************************************************************************
***************************************************************************
* TechNet mail list is provided as a service by IPC using SmartList v3.05 *
***************************************************************************
* To unsubscribe from this list at any time, send a message to: *
* [log in to unmask] with <subject: unsubscribe> and no text. *
***************************************************************************
|
