Solderability is achieved through solvent and aqueous cleaning,
burnishing, and pretinning. Plating with gold and nickel can replace
Burnishing is the most frequently used process, as it removes
oxides as well as binder glass. The mechanical abrasion of the surface is
accomplished with the use of an abrasive eraser, fiberglass brush and/or
abrasive pad. The burnishing operation helps remove surface oxides and trace
glasses which might otherwise interfere with good solder wetting.
Pretinning is accomplished by applying solder using solder paste
reflow or solder dip, followed by subsequent removal of excess solder.
Pretinning works as a successful screen to pinpoint difficult-to-wet
conductors, prior to committing the MIB to assembly as well as preparing the
conductors for the solder operation. Proper preheating of the MIB may be
required in order to minimize the possibility of thermal shock damage during
A thin layer of nickel and gold is sometimes applied to the
solder area during MIB fabrication to improve solder wetting and to prevent
oxidation of the solder pads. Electroless plating techniques are required to
plate pads which cannot be electrically tied together. Special care is
required to insure that plating solutions do not permeate into the porous
Leadless Chip Carriers
Solderability is achieved through cleaning and pretinning. The
pretinning operation includes application of flux and solder and can be done
either manually, by dipping the LCCs into a solder pot, or by an automated
method. The manual procedure requires operator skill to insure consistent
solder coverage. The automatic methods achieve consistent results and are used
for high volume applications. Two automatic methods commonly used are "mass"
tinning of LCCs via wave soldering, and an assembly line approach using a
"ferris wheel" arrangement to dip the LCCs into the molten solder. In both
these methods the device is retained by magnetic pickups, vacuum, or
pressure-sensitive tape. Large packages require special care, e.g., preheating
may be required to prevent thermal shock damage.
Solderability is achieved through barrier metallization and
pretinning. Barrier metallizations such as nickel serve to protect the base
metallization, which is usually silver or silver alloys, from the leaching
effects of soldering. The leaching of silver into solder solutions results in
grainy solder joints (intermetallics) and demetallized terminations.
Leaded Components and Connectors
Solderability is achieved through pretinning prior to module
Visual inspection of the pretinned parts at approximately 10X
magnification verifies the acceptability of pretinning.
Parts should be inspected for proper wetting, damage, excess
solder (bumps), solder shorts, and evidence of leaching.
STORAGE OF PREPARED COMPONENTS
Storage of the pretinned parts and prepared components in
nitrogen is recommended to minimize oxidation or other