LeRoy,
It's not that the surface is oxide free, it's just thin, uniform and stable enough at high temperature (375F) to provide protection to the copper. For best results in circuit manufacturing, the passivation
treatment should be removed prior to photoresist application or plating. Failure to remove the passivation treatment from the copper surface may result in delamination at photoresist or coverlay application,
pinholes at plating, dewetting at solder application, or other adhesion related problems.
Generally, the 50 to 75 angstrom thick passivation layer is thin enough that you don't have to worry about troublesome levels of chrome in your waste stream, but most shops these days want to avoid
maintaining a chrome containing process. One of our solder experts will have to address the issues of zinc chromate compatibility with tin lead solder.
Andy Magee
Flex Guru - Consulting
[log in to unmask]
(937) 435-3629
LeRoy Forney wrote:
> Guru Andy - Based on your "ps": How does zinc chromate passivation fit into the general picture of copper solderability? Could it be used instead of or along with OSP coatings to reduce copper oxidation?
>
> - LeRoy
>
> -----Original Message-----
> From: Andy Magee [SMTP:[log in to unmask]]
> Sent: Saturday, July 24, 1999 8:08 AM
> To: [log in to unmask]
> Subject: Re: [TN] Copper oxide removal
>
> Sulfuric is preferred over Hydrochloric for oxide removal because HCl
> tends to increase in etch activity as the dissolved copper concentration
> goes up with use. 10% H2SO4 will be a much more stable and reliable
> process for oxide removal. Save the nitric for things like stripping
> copper off your plating racks.
>
> Andy Magee
> Flex Guru - Consulting
> [log in to unmask]
> (937) 435-3629
>
> ps. Initially copper foil is provided from the supplier with a zinc
> chromate passivation coating to prevent oxidation. Since this angstroms
> thick, relatively brittle, layer may not be uniformly intact it should
> be removed with a process that will not attack the copper before
> microetching. 10% H2SO4 is clearly the preferred choice over HCl, but
> there are also a number of proprietary acid/surfactant mixtures that are
> widely used for this.
>
> LeRoy wrote,
>
> Subject: Re: Copper oxide removal
> Date: Fri, 23 Jul 1999 15:56:52 -0400
> From: LeRoy Forney <[log in to unmask]>
>
> My understanding of the usual oxide removal procedure is a 3-minute soak
> with 5%HCl. The goal is a very mild
> etch, and I've heard that nitric acid will cause pitting instead - and
> this is in line with some laboratory
> oxidation studies I did some time ago. Variability in solderability
> data was much higher on aged coupons I had
> treated with dilute HNO3 than on coupons treated with 5%HCl.
>
> LeRoy
> -----Original Message-----
> From: nishath yasmeen [SMTP:[log in to unmask]]
> Sent: Friday, July 23, 1999 3:34 PM
> To: [log in to unmask]
> Subject: [TN] Copper oxide removal
>
> Hello everyone!
> Is Nitirc acid ( dilute) a better acid than sulfuric for cleaning
> the oxide on plated copper?
> Any information provided will be appreciated.
>
> Yasmeen
>
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