Cauterisation and Environment - HARKE Group

0. Topic
Cauterisation and Environment
Imaging
The here available article discusses the question of selection, potential dangers and environmental safety of
caustics. The article is to be understood as approach to confront a nuts and bolts basis to the more and
more critical attitude of this topic and the high information demand of the user side.
The properties of various caustics, their application and pros and cons are subject of the first chapter. In the
second the question of conditioning rinsing waters by means of aftertreatment methods is being discussed.
The summary in the third paragraph tries to evaluate the actual state and possible perspectives without
wanting to solve the goal conflict between environmental safety and cauterisation technique.
1. Caustics
For chemical purposes we generally differ two groups of caustics, namely acid and alkaline media.
The most known agents of this group are ferric-III-chloride, ammonium sulphate and sodium persulphate as
well as agents on basis of hydrochloric acid / hydrogen peroxide.
Especially when producing double-sided, plated though PCBs in metal resist technique the known
ammoniacal media used in large plants have lately gained in importance also in laboratories.
1.1 Ferric-III-Chloride
Ferric-III-Chloride (FeCl3) is one of the oldest caustics. Although losing importance over the years, it seems
to nowadays rebound because of its comparably unproblematic handling as far as one or two-sided, non
galvanic plated through PCBs are being produced.
1.1.1. Characteristics
The product combines the advantages of a fast and high-definition cauterisation and an acceptable copper
capacity. Ferric-III-chloride solution cauterises in a cold stadium already, does not tend to corrode and has
almost an unlimited shelf life when unused.
Mud formation and the contamination of units, clothing and working places are considered as major
disadvantage of FeCl3. Constructive measurements at the cauterisation machines and by adoption of a stain
remover this has been accommodated as far as possible and economically justifiable.
1.1.2 Supply Conditions
Ferric-III-Chloride is being offered in different ways, either as ready made solution, as granules or as
ultrapure and highly reactive sublimate. The content of the ready made solution mostly is up to 45 % FeCl3.
With respect to the copper capacity and cauterisation speed the optimum concentration lies according to
experience at 30 - 35 %. Disadvantages of the simple use of ready made solutions are the high transport
weight and the dangerous goods aspect during transport.
Only special formulations offer advantages here that work on a low temperature level and without any mud
formation. The sublimate with a content of 98 99 % FeCl3 is the purest and most efficient form of ferric-IIIchloride.
Its handling, however, demands highest preventative measures. The product is most hygroscopic,
i.e. it absorbs water (e.g. humidity). At the same time the dissolving reaction proceeds strongly exothermally,
that means under heat development. Contacting the skin danger of burning and corrosion exists. It is
mandatory to wear acid-proof gloves, face masks as well as an apron. The dissolving process has to be
proceeded step by step in a heat and corrosion resistant bin outside the cauterisation machine. Because of
its high purity and productiveness (300 350 g/l solution) the sublimate is liked to be used despite all of these
disadvantages.
© Aicello Chemical Europe - Xantener Str. 1 -45479 Mülheim an der Ruhr - Matthias Stange, Phone: +49 (0)208 / 3069 1530, Mail: sta@harke.com

Imaging
The granules consist of about 60 % FeCl3 and 40 % chemically combined water and other substances. The
less content of active substances require a larger quantity use than the sublimate, the granules, however, do
not react exothermally when dissolving in water and therefore are much easier to handle. From 800 g
granules 56 % and 1 l water one gets about 1.4 litre 32 % solution.
1.1.3 Application
In an aqueous solution of ferric-III-chloride copper oxidizes to copper-II-chloride while the cauterisation
agent passes into the less inferior ferric-II-chloride. At a make-up quantity of about 35 w/w % FeCl3 the
maximum capacity of the cauterisation solution calculatively adds up to about 50 g copper / litre. The
cauterisation duration in a fresh solution of about 45°C under optimum machine conditions lies in the range
of about 2 seconds per 1 µm copper. It increases at first only slowly during the increasing consumption rate,
but before reaching the saturation point rapidly. The calculatively possible copper absorption is in practice
not being realised because of the decelerated cauterisation process and the increasing undercut of the
pattern plate. Shortly before the saturation limit the cauterisation agent tends to intensify the formation of
ferric- and copper chloride mud so that the cleaning process of the machine reasonably increases. The
increase of the cauterisation duration to about the double start value therefore marks the economically most
favourable moment to replace the cauterisation agent.
1.1.4 Environmental Compatibility
Used ferric-III-chloride solution cannot be recycled with justifiable costs. The possibility to dilute the solution
by adding hydrochloric acid and at the same time to delay the starting mud formation is in practice not being
used because this process will only be effective for a short time. An imaginable point for recycling according
the latest legal situation would only be the acid concentration or the precipitation of the heavy metals from
the solution and their afterwards smelting. According experience this recycling possibility, however, is only
being met to a limited extent. Failing other alternatives the used solution has to be disposed as hazardous
waste.
In order to avoid a contamination of the workplace by cauterisation vapours, sufficient room ventilation is
necessary when using ferric chloride. The aerosol formation especially appearing in spray cauterisation
machines may lead to mucous membrane irritation. Additionally cauterisation vapours corrosively effect
metal objects in the room strongly.
1.1.5 Evaluation
Cauterisation and Environment
The handling of ferric-III-chloride in form of granules is unproblematic. The use of the sublimate is subject to
a strict due diligence when newly preparing the caustic solution. The sublimate is recommended because of
its productiveness and unproblematic cauterisation behaviour for the use in often utilised or quasi continuous
used laboratories. With reference to the hazardousness of the real ferric-III-chloride it has to be mentioned in
the margin that it is being used in for instance waste water treatment plants as flocculants. Because of the
possible copper content in the consumed solution it has, however, to be categorized as hazardous waste.
© Aicello Chemical Europe - Xantener Str. 1 -45479 Mülheim an der Ruhr - Matthias Stange, Phone: +49 (0)208 / 3069 1530, Mail: sta@harke.com