We had to stop using U/S baths because of detrimental impact on bond
wires and thickfilm conductors. We paid for an investigation many
years back. I have the report somewhere. If I find it, I can send some
pics to Steve's gallery. As usual, you need know exactly what you are
doing. With correct liquid density vs. the electronic parts, correct
frequency and energy, I think U/S cleaning is not at risk. The problem
is to get operators with this insight, when even the engineers have little
knowhow in this area.
Ingemar Hernefjord
Ericsson Microwave Systems
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]
Sent: den 4 mars 2005 19:12
To: [log in to unmask]
Subject: [TN] Ultrasonic
Is ultrasonic cleaning coming back? found this article in http://ieeexplore.ieee.org/iel5/8909/28167/01260581.pdf?arnumber=1260581
Ramon
3.1 UItrasonic energy
Micro-vibrations in the liquid cause cavities
(vacuum "bubbles") by which contracting a very
intensive scrubbing effect is generated. The more
energy density, the higher effect is produced, but
because of it's cavitation character, it can also damage
the basis material. This is why many of assemblists do
not like to use ultrasonic energy at all. Statistics show,
that millions PCB's /year are cleaned with help of
ultrasonic, but very little defect is observed. If a proper
intensity, frequency and time is taken, there is no risk
of mechanical damage. Also the original MIL
longer cycle times.
3.4 Air bubbling
This agitation is very effective, especially for
equalizing the concentration of impurities after they
have been removed from the surface. It can be used as
the consequent after Ultrasonic agitation, hut in the
next cycle a de-gassing procedure must follow.
3.5 Temperature
Increasing the temperature is a common means to
speed-up dissolving. Some agent requires specific
temperatme range (micro-emulsion process 20-50°C).
In some cases, increasing of temperature might cause
worse cleaning results. (white residues or damaged
solder resist). White residues might be resulting due to
polymeration of resin in higher temperatures instead of
dissolving them)
4. MACHINES FOR CLEANING
Apart of different other cleaning tasks , which are
mainly cleaning of machines and tools, cleaning
substrates after soldering and stencils for solder paste
and glue printing is a major application, which uses
machines.
The main problem building of machines for
cleaning is, that every application is slightly different.
This is caused by many factors. Different material of
cleaned parts, different chemistry used, different.
soldering parameters (cause different grade of
polymeration of synthetic resin , which fluxes
contains), different capacity.
standards, which prohibits US cleaning is no valid any
more and new lF'C standards does not speak about
such ban.
Therefore to build a good machine, with perfect
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