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Gold surface contam after prebake 150C for 3 hrs

ccl

#27930

Gold surface contam after prebake 150C for 3 hrs | 6 April, 2004

hi, i encounter gold surface contam issue on wire bonding ring after prebake at 150 C for 3 hrs, tis cause wire bonding non stick issue. the contam seem begin at the solder mask area toward center of the bonding ring, but is not consistance. any suggestion how to cater this problem?

thk. ccl

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#27936

Gold surface contam after prebake 150C for 3 hrs | 6 April, 2004

It doesn't make sense that contamination would form on your gold pads after prebake of 150C for 3 hrs. The contamination must have been there prior to the bake.

Your description makes us think of solder mask bleed. Tell us about: * Solder mask * Solderability of the contaminated area * Type of wire bonding that you're doing * Actual gold and nickel underplate on your pads

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ccl

#27946

Gold surface contam after prebake 150C for 3 hrs | 7 April, 2004

thanks Dave, solder mask use is AUS 5 from Taiyo ink, solderability of the contam area is still pass the min spec. gold thickness is ~ 1 um and Ni layer is ~10um.

can solder mask bleed cause contam? forget to tell the product is full body gold (FBG). can it be cu diffusion from the base cu? or ...

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#27961

Gold surface contam after prebake 150C for 3 hrs | 7 April, 2004

We're not familiar with the AUG5 from Taiyo. [It doesn't show on their US site.] Is it liquid photoimageable? Printed solder masks are more likely to bleed. But you wouldn't have any solderability with bleed.

Your plating seems acceptable [if that's what you're receiving]. * Poor coverage at the edge of the gold pads (exposed Cu or Ni) sometime will result Cu/Ni migrated to Au surface under humidity condition. (surface diffusion is 2 orders of magnitude higher than the bulk diffusion). * Insufficient final rinse (or delay of the final rinse, e.g. "went for lunch") after the plating may cause residue on the gold pad (oxidation of residue...e.g. brownish look Au for KCN based plating). * Good reference: "The Auger Analysis of Contaminants that Influence the Thermocompression Bonding of Gold" G.E. McGuire et. al, Thin Solid Films Vol. 45, 1977. p. 59 * Plating condition [e.g. current density, PH, additive concentration variation] can entrap impurities (co-deposit), sometimes the Au deposit becomes porous. A good reference paper for Au plating is: "High-Performance Gold Plating for Microdevices" A. Gemmler et.al. Plating and Surface Finishing, Aug. 1994, p.52; Publisher - Association of Electroplaters and Surface Finishers (AESF) Printers

Whem wire bonds don't stick when bonded: * Check pull and shear strength * Review machine setup parameters, depending on point of failure * Listen during bonding, if there is a high pitch buzz, there is vibration in the system somewhere, "seek and destroy" * Get the plating analyzed, and look for high surface contaminants.

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ccl

#27984

Gold surface contam after prebake 150C for 3 hrs | 10 April, 2004

u are right, Dave, AUS 5 is a LPISM paste.

Thanks a lot for the advise and ref. given.

rgd ccl

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Kris

#29891

Gold surface contam after prebake 150C for 3 hrs | 5 August, 2004

All

Can someone explain what full body gold is ?

Any reference material to read from ?

Thx

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#29897

Gold surface contam after prebake 150C for 3 hrs | 5 August, 2004

Well, it could be the beautiful Jill Masterson, as Goldfinger's trusted card advisor Shirley Eaton, who gave new meaning to the phrase "golden girl."

Or more mundanely, gold thickness usually ends-up: * Gold fingers (10 to 100 micro-inches) * Selective Gold (10 to 100 micro-inches) * Full Body Gold (10 to 100 micro-inches) * Immersion Gold (2 to 10 micro-inches)

So, we'd guess that your "full body gold" is electroplated.

This is "standard old guy" talk. Check with your board fab for comfirmation.

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