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           Spray Cleaning Of PCBs
           In Industrial ‘Dishwashers’
                                                                                                           by Stefan Strixner,
                                                                                                              Zestron Europe

           Spray cleaning processes have be-         An optimised
           come increasingly popular in the          cleaning process
           European electronics manufactur-
           ing industry. These processes, based      An optimised ap-
           on dishwasher-type systems, are           proach to this
           used especially when limited num-         type of cleaning
           bers of boards need to be cleaned,        system is the wa-
           and are an alternative to inline          ter-based Micro
           cleaning. In addition to small foot-      Phase Cleaning
           prints, spray cleaning processes are      (MPC) process.
           also economical and flexible.              In contrast to
                                                     traditional sur-
                                                     factant systems,
                                                     a special feature
           The dishwasher process                    of the patented
                                                     MPC technology
           The cleaning principle of industrial      is that the active
           dishwasher equipment (Figure 1) is        cleaning compo-
           similar to that of a household dish-      nents do not bind
           washer and hence very accessible to       to the removed Figure 1 - Miele IR 6001 washer
           users. Of course, the materials used      contaminants.
           are adjusted to the requirements of       The microphases
           an industrial cleaning application.       temporarily re-
           Furthermore, in an industrial sys-        tain the impu-
           tem, the cleaning medium follows a        rities and then
           closed loop so that it is used numer-     release them to
           ous times. Spray cleaning as well         the filter which
           as the subsequent rinsing steps are       removes      them
           gentle and carried out at a relatively    from the clean-
           low pressure.                             ing agent. With
                                                     this technology,
           As illustrated in the process flow         active cleaning
           chart (Figure 2), the cleaning            agents are not se-
           agent is pumped from the holding          lectively depleted Figure 2 - Process flow chart for spray cleaning in a
           tank into the cleaning chamber            during the clean- dishwasher-type equipment
           and heated up to the preset oper-         ing process. In
           ating temperature. As soon as the         addition, the col-
           selected operating temperature is         lected dirt can be easily removed organic and inorganic impurities,
           reached, the actual cleaning process      from the system using simple bath including salt-like residues, are
           starts. After cleaning is completed,      treatment processes such as filtra- removed in a single process. Due
           the cleaner is pumped back to the         tion. Consequently a significantly to the special surfactant-free for-
           holding tank where it is stored for       longer bath life as well as lower mulation, electronic assemblies
           subsequent cleaning cycles. After         process costs are achieved in com- are rinsed and dried residue-free.
           various rinsing steps with softened       parison to solvent or surfactant Lead-free solder pastes have also
           or demineralised water, the cleaned       cleaning processes.                  been subjected to comprehensive
           parts are dried with hot air. Ad-                                              tests and can be easily removed.
           ditional metering channels allow          MPC agents were specially devel-
           more additives to be supplied, such       oped for the high precision clean-
           as inhibitors or defoamers. If re-        ing of electronic assemblies and The process in action
           quired, a range of different baskets      are suitable for a broad range of
           allows items with a wide variety of       flux removal applications. Both The combination of a dishwasher
           geometries and sizes to be cleaned.       polar and non-polar contaminants, equipment with an MPC cleaning

           OnBoard Technology April 2007 - page 56                                       
                                                           HL Planartechnik          HE - System-Electronic
                                         Medium            Vigon A 200 (30%)         Vigon A 200 (20%) + 1% Vigon CI 20
                                         Temp.             50°C                      50°C
                                         Time              10 min                    10 min
                                         Rinse 1+2
                                         Medium            Softened water            Softened water (+ Defoamer 30)
                                         Temp.             RT                        RT
                                         Time              3 min in each case        1 min in each case
                                         Rinse 3+4
                                         Medium            Demineralised water       Demineralised water
Figure 3 - Inclination sensor by HL
Planartechnik                            Temp.             40°C + 50 °C              50°C
                                         Time              3 min + 2min              2 min in each case
agent allows the use of standard so-     Drying
lutions for a wide range of cleaning     Medium            Circulating air
needs. This is also shown by appli-      Temp.             100°C                     115°C
cations at HL Planartechnik (a divi-     Time              30 min                    35 min
sion of Measurement Specialties) in      Overall process   50 min                    50 min
Dortmund (Germany) and HE - Sys-         time
tem-Electronic in Veitsbronn near
Nuremberg (Germany). Both man-          Table 1 - Process parameters compared
ufacturers employ a spray cleaning
process with a Miele IR 6001 washer     the subsequent wire bonding pro-          the most diverse production re-
(to be replaced by the Miele IR 6002    cess. Approximately 4-5 loads are         quirements and can be used for a
in the future) and the water-based      cleaned per day. The water-based          broad range of cleaning applica-
MPC cleaner Vigon A 200, but for        MPC spray cleaning process im-            tions in the SMT industry. Its high
different applications.                 plemented after converting to the         degree of flexibility also provides
                                        lead-free soldering process gave          potential cost savings to companies
At HL Planar-technik, inclination       better results than the previously        with a range of different cleaning
sensors (Figure 3) are cleaned after    used solvent cleaning method. With        requirements.
soldering. Since the inclination sen-   the process parameters
sors are supplied to the automobile     shown in Table 1, the
industry, the high cleaning standards   required thresholds for
typical of this sector must be main-    the ionic contamina-
tained. Colophony residues from the     tion were easily met
soldering process with a high lead-     and bondable surfaces
containing solder wire must be re-      ensured.
moved completely (Figure 4).

Additionally, after cleaning a bar      Other applications            Figure 4 - Inclination sensors before cleaning
code is applied to the sensors by                                     (left) and after cleaning (right)
an inkjet printer, which requires a     A Miele IR 6001 / Vigon
                                                                                                                              P A C K A G I N G

printable, flux-free ink-adhesive sur-   A 200 cleaning process
face. The throughput can reach up       has a wide spectrum
to 3,000 units per day and the rate     of cleaning applica-
is increasing. By introducing an op-    tions and requests
timised cleaning process (Table 1),     little customisation.
the desired reproducible results are    In addition to the ap-
achieved.                               plications described
                                        above, the cleaning
At HE - System-Electronic, 10cm         of misprinted PCBs is
x 10cm ceramic hybrids (Figure 5)       also feasible. By using
                                                                                                                              A D V A N C E D

and FR4 assemblies are cleaned after    an appropriate clean-
reflow and comb soldering process-       ing medium, stencils
es. These products are also manu-       or solder frames and
factured mainly for the automotive      condensation       traps
industry.                               can also be cleaned.

The cleanliness requirements are        This completely auto-
geared toward the J-Std 001D and        mated process meets           Figure 5 - Ceramic hybrid circuit by HE - System-Electronic                                                        OnBoard Technology April 2007 - page 57

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