GENERAL INFORMATION
AMTECH RMA-223 is a cream conforming to ANSI/J-STD-004 - 006. It
is specially designed for today's SMT applications. It is a
homogeneous mixture of the highest quality pre-alloyed solder
powders and mildly activated resin paste flux. With a special blend
of gelling additives in this formulation, it prevents segregation of
solder cream and provides a creamy mixture ready for application.
The residue from RMA-223 is light amber & clear of solder balls.
The solder cream is available in a wide range of solder alloys,
metal percent loadings, and mesh sizes which give desired properties
to meet different applications.
APPLICATION INFORMATION
RMA-223 solder cream can be applied in precise amounts to any
configuration of solderable surface using techniques such as screen
printing, stenciling or dispensing.
The common techniques for reflow soldering are suitable for use
with this solder cream. Because of the various types of reflow
equipment, different thermal mass and thermal conductivity of the
substrates, different components to be soldered and the metallurgies
of the solder, the optimum reflow profile shall be determined by the
user. The guidelines set below should give a good starting point.
The cream is specially developed with a non-hygroscopic activator
system, which not only gives excellent solderability but also is
less susceptible to humidity. Its residue is
non-conductive/non-corrosive and therefore may be safely left on the
boards without cleaning. The residue has a high Surface Insulation
Resistance in a few orders of magnitude higher than the 100 m-Ohm
requirement set by the IPC international standard.
RMA-223 uses a modified rosin which after reflow gives much
lighter residue than traditional "RMA" solder pastes. It
is therefore cosmetically more acceptable to end users.
With the selection of fine mesh powders such as -325/+500, it can
be used for fine pitch assembly application. For ultra fine pitch
assembly we recommend our -400/+500 mesh powder.
PROCESS SET-UP FOR RMA-223 SOLDER CREAM
PRINTING
There are various methods for solder cream application, the most
popular is metal stenciling. Advantages of this method are, longer
utility life, and its ability to give better printing resolution for
fine pitch designs compared to screens; and higher throughput and
consistency of deposition compared to syringing methods.
For stencil printing the following parameters are recommended for
initial evaluation of the cream:
Squeegee speed: 20-40 mm/sec.
Squeegee pressure: Just enough to sweep the cream from the
stencil, too high a pressure will cause scoop out and a thin
deposition, too low a pressure may cause smearing and bridging.
Squeegee hardness: 80-90 durometer for 25-50 mil pitch
90-110 durameter or metal blade for 25 mil and below.
For ideal stencil life and printing performance, the environment
should have a temperature between 20-25o C and relative humidity
less than 65%.
COMPONENT PLACEMENT
The deposited solder cream will possess strong enough tackiness
to hold the components and prevent misalignment for an exposed
duration of at least 8 hours. However, it is always advisable to
place components immediately after printing. The tackiness data
shown in the property table is obtained by the use of a Chatillon
Tack Force Measuring instrument in accordance with IPC test methods.
REFLOW SOLDERING PROCESS
There are a few main methods for solder reflow, namely infrared,
hot air, and vapor phase. The most popular designs are convection or
a combination of convection and IR. Heat transfer in these ovens are
convection with additional energy from radiation.
To properly profile a board you must measure the actual temperature,
placing thermocouples at the solder joints of at least three
different sized components on the board. This will allow the
determination of a profile that will give sufficient time and even
heat distribution to all components on various portions of the
board.
It is recommended to have a smooth and slow ramp in the profile. The
soaking time (temperature between 150-180o C) should not be more
than 2 mins. Dwell time (temperature above liquidus point) should be
30-70 sec.
CLEANING PROCESS
As this paste is classified as RMA, its residue can be safely
left on the board without cleaning. If cleaning is needed
fluorinated or chlorinated solvents can be used. Saponifiers or
semi-aqueous methods will also remove the residues.
STORAGE
RMA-223 should be stored @ 40o F (4o deg C), allow to come to
room temp. before opening. Unopened jar properly stored will have a
minimum shelf life of 6 months.