>Having used DMAB for several years now, we can state that it does work
reliably. In our validation testing process, we performed extensive analysis
on the post DMAB surface and found that both the micro-topography was
dramatically reduced and the level of oxidation almost zero. This explains
why it works. Quite simply the chemical reaction is based on basic chemistry :
>
> METAL oxide + Acid = METAL + water
>
> CuO + 2H(+) = Cu + H2O
>
>If DMAB eliminates, or at least dramatically reduces (no pun intended) the
oxygen from the left hand side of this equation, then there is no reaction
with the available acid that would result in pink ring. The natural chemical
reaction ceases to occur. On the other hand... if there is a high level of
oxidation as is found in typical BLACK oxide, then this natural chemical
reaction cannot be avoided.
>----------
>
>>There are some things that I can't understand about the black oxide, pink
>>ring and the use of DMAB
>>Pink ring is the result of the attack of BO by acids in the electroless
>>copper line. DMAB prevents this attack.
>>The black oxide treated with DMAB can resist a lot of time in a 10% HCl
>>solution but only a mom in a sulphuric/hidrogen peroxide solution. Then, why
>>we don't have pink-ring using DMAB?
>
>----------
>I suspect that by the description given, you are ETCHING copper using
Sulfuric/peroxide solution. The visible attack that you see is actual
removal of copper (and the slight layer of brown after DMAB processing).
This is not oxide attack but rather a chemical removal of copper including
the surface colouration.
>----------
>>
>>The peel-off for the black oxide treated is lower than the non treated.
>
>----------
>Our analysis did exhibit slightly lower peel strengths after post-treatment
but remember... the adhesion you measured was on black oxide. Should the
oxide layer be removed by acid as per the above reaction... then you
eliminate the very layer that provides this 'good' adhesion. I would
recommend that you consider an alternative measurement for bond integrity
such as TMA260.
>----------
>
>>During the drilling , I think it would be easier to delaminate. Again ,why
>>we don't have pink-ring using DMAB?
>>
>>I would like to understand how DMAB works, because sometimes it doesn't do.
>
>----------
>When DMAB fails to perform properly it is usually due to:
>
>1) Poor chemical control of DMAB solution (concentration, pH etc.)
>2) Surface contamination after treatment (fingerprints etc.)
>3) Post oxide baking at too high a temperature (reoxidizes copper)
>4) Poor rinse quality after treatment (watch you water purity)
>5) Improper drying and/or storing conditions after processing.
>----------
>
>>Is there another systems to protect de black oxide?
>
>----------
>There are other post treatment reducers but all are based on the avoiding
the chemical reaction outlined above.
>----------
>
>>
>>I would like also to find some papers, articles, etc. about this process.
>
>----------
>There have been several good papers on pink-ring dating back several years.
Probably the best source of these is your chemical supplier of DMAB. If not
please E-mail your address and I'll send you some reference material.
>----------
>>
>>Thanks and excuse my bad english.
>>
>>
>>Toni.
>>
>>
>>
>================================================================
>
> Please find these previous E-mails regarding Pink ring :
>
>================================================================
> Pink Ring can better be termed "Pandora's Box". This is because
> it's source(s) can be many. Isolating the source(s) can easily
> confound a process engineer (trust me, I know). Rudy has outlined
> where the dissolution of the oxide takes place. To name just a few,
> a couple potential sources could easily be improper Rate of Rise in
> lamination (rendering a non fully wetted oxide to laminate
> interlaminar bond), drilling parameters, the new (fun) HTE copper
> foils that are more malleable than the the lower (harder) grade
> foils,...etc. The bottom line is that somewhere, somehow a small
> weak point develops around a drilled hole. That weak point is where
> the acid chemical attack to the oxide on the plane develops and can
> be seen. They key point is that pink ring has been with us for years
> and has plagued the PCB fab shops to try to isolate it's source.
> Minor Pink Ring has been found to not impair the electrical or
> mechanical performance of the PWA. (Cosmetically it's not appealing
> but it meets Fit/Form/and Function) Major pink ring is an issue.
> If the pink ring is significant enough to the point to where there
> is a profound separation at that innerlaminar bond location, then
> during subsequent wet processing, a plating "wedge void" could easily
> develop. This is where a plating thickness can easily fall well below
> .001" thk and could possibly even have some copper voiding (abscense
> of copper). Generally, those locations have massive pink ring way up
> the plane(s). Micro section evaluation will detect this condition or
> PTH NDT (Non-destructive testing). With the advent of post oxide
> conversion or reduction coupled with better copper plating chemistry
> that produces better distrubution, leveling, and throwing power we
> (fabricators) are able to produce far better product than say 10 years
> ago.
> Yes, reducing stack heights and shortening times in acid solution
> will minimize the amount of oxide dissolution on the plane(s). And
> this may be a fine fix for a shop that has the capacity and scheduling
> to accommode for this, but for a larger shop that is QTA and
> semi-production orientated, we must optimize our processes to produce
> premium quality at a "fast pace". Yes, sometimes the cost (like the
> plating chemistry) is expensive, but the competition is fearce.
> (Sometimes compromises are not an option)
> Shops now a days should not be plagued with pink ring. It should be
> a thing of the past. I don't believe oxide conversion/reduction is
> hiding the issue. If a fab shop runs routine cross sectional analysis
> and cross checks PTH integrity by PTH NDT, then they would know and
> capture any PTH anomaly that would be considered an issue as
> previously outlined.
>
> Groovy
>
> (PS-Rudy, DMAB is not the only post oxide process out there you know)
>
>______________________________ Reply Separator
_________________________________
>Subject: Re: pink ring
>Date: 2/5/96 10:36 PM
>
>-----------------------------------------------
>Just to make sure that we all are beginning at the same point, Pink Ring is
>caused by the dissolution of the oxide layer on the innerlayers. The oxide
>is black, and when it dissolves, the"Pink Ring" of Copper under the oxide is
>exposed.
>
>As has already been written, Pink Ring has many causes, and even when the
>process is seemingly perfectly in "spec", it is still possible to get Pink
>Ring, which is the principal reason why most PCB fabricators use a DMAB
>reduction step at the end of the oxide line. The DMAB renders the oxide
>insoluble to any of the subsequent process chemicals, thus effectively
>eliminating Pink Ring. This step eliminates the appearance of Pink Ring, but
>it is thought to be a largely cosmetic effect.
>
>Many studies have been done on Pink Ring causes, and after you get by the
>obvious process problems, such as leaving the panels too long in the HCl
>containing steps, there were two main "causes" of Pink Ring. Pink Ring could
>be avoided in most cases by drilling shorter stack heights. The other place
>that Pink Ring was observed to occur was in the Acid Copper Plating bath.
> This is clearly due to having porous, or voids in the electroless Copper
>deposit.
>
>It has been pretty clearly demonstrated that moderate Pink Rink has virtually
>no effect on the performance of the board in service, but yet for years, it
>was a major cause of rejection of finished PCB's.
>
>Rudy Sedlak
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>
D. Rooke
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