Brian: In this explanation, you are assuming that the whole, let's say, PWB
will be considered the "homogenous" material, and perhaps this will become
the accepted understanding. I was thinking in terms of the coating itself
being the homogenous material in which the threshold quantity needed to be
evaluated...
jw
Jerry Wagner Dept 0056 Environmental Engineering B096-1
x56275 pg 58888-0658 (607)755-6275 fax: (607)755-6282
Huron Real Estate Associates, LLC and Endicott Interconnect Technologies,
Inc.
Via the Internet: [log in to unmask] [NOTES: Jerome Wagner/Huron/EIT]
Brian Ellis
<b_ellis@PROTONIQ To: [log in to unmask]
UE.COM> cc:
Sent by: Leadfree Subject: Re: [LF] Chromate conversions
<[log in to unmask]
>
02/20/2004 11:19
AM
Please respond to
"(Leadfree
Electronics
Assembly Forum)";
Please respond to
Brian Ellis
Again, we are talking about single sided coating, so you can halve the
thickness of metal in my previous post, which is still thicker than the
EDCF used on PCBs. However, you also have epoxies and glass fibres
(assuming FR4) to form the bulk of the weight. I doubt whether you have
anything to worry about. If you have doubts, weigh a typical etched PCB,
dissolve all the metal and analyse to find the weight of chromium. If it
is >0.1% of the total then ask your supplier to use an alternate
adhesion-enhancing finish, although I'd be surprised if this were
necessary.
Brian
Jerome Wagner wrote:
> Brian, Others: I have an add-on question. I am aware of zinc-chromate
> surface treatment of copper foils which are used for wiring in PWB's. I
> have been told that the CrVI is converted to CrIII (or, let's say, not
> CrVI) in their process; further, that some CrVI is likely to remain
despite
> the processing. I am concerned about applicability of RoHS to my products
> due to this possible trace of CrVI (which problem would be exacerbated if
> "intentional use" remains, I would argue).
>
> Your inputs on this? Thanks. jw
>
> Jerry Wagner Dept 0056 Environmental Engineering B096-1
> x56275 pg 58888-0658 (607)755-6275 fax: (607)755-6282
> Huron Real Estate Associates, LLC and Endicott Interconnect
Technologies,
> Inc.
> Via the Internet: [log in to unmask] [NOTES: Jerome
Wagner/Huron/EIT]
>
>
>
>
> Brian Ellis
> <b_ellis@PROTONIQ To: [log in to unmask]
> UE.COM> cc:
> Sent by: Leadfree Subject: Re: [LF]
Chromate conversions
> <[log in to unmask]
> >
>
>
> 02/20/2004 10:25
> AM
> Please respond to
> "(Leadfree
> Electronics
> Assembly Forum)";
> Please respond to
> Brian Ellis
>
>
>
>
>
>
> I don't understand the problem. Chromate conversion coating is usually
> about 1 µm thick. Less than 1/3 the weight of zinc chromate is chromium.
> The density of ZnCrO4 is roughly 1/2 that of steel. So if your steel is
> more than 0.33 mm thick (assuming both sides are conversion coated),
> then you will be under the 0.1% limit for flat surfaces. As hardware
> with a convoluted surface, such as screws, is usually pretty bulky, I
> see no problem there. You could always weigh your parts, chemically
> dissolve the conversion coating and analyse to determine the weight of
> chromium: I'll bet a pound to a penny that very few items (very small,
> thin, convoluted parts) would exceed your 0.1%.
>
> If you have transparent, colourless, chromate conversion coatings, these
> must be very thin (less than 1 µm). Zinc chromate is a quite deep and
> intense yellowish colour.
>
> If you're still scared, there are other conversion coatings, such as
> oxidation and phosphatation.
>
> Brian
>
> to Paul Taylor wrote:
>
>
>>Dear All
>>
>>this question is a more RoHS orientated, however it is associated with
>>metallurgy, I'm a bit confused as I'd not heard of it before.
>>
>> What chromate conversions involve Hexavalant Chrome (this applies to
>> fixings, screws etc). I've been told that both the Nickel Plate and
>> Zinc Chromate platings use Hexavalant chrome. Is this true? or have I
>> been miss-informed.
>>
>> The issue fo us especially concerns steel parts that have a zinc
>> chromate finish. This is also known as zinc clear and /or zinc clear
>> chromate. The problem is that this process results in the part having
>
> a
>
>> coating of Hexavalent VI chrome. I am not a metallurgist, but have
>
> been
>
>> informed that when tested, the directive of having no more than 0.1%
>
> by
>
>> weight will be exceeded, by parts large in surface area.
>>
>>regards
>>
>>Paul
>>Paul R Taylor
>>Technical Advisor
>>Pitney Bowes Ltd email: [log in to unmask]
>>
>
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