Quality Control and Inspection Operations
I1.
visual inspection of
joints
-
is a manual inspection for the following characteristics: 1) degree of wetting
of the surfaces to be joined. 2) contours of the joint fillet (indicates the
volume of solder in the joint), 3) evidence, if any, of thermal damage to the
surrounding area or components, 4) cleanliness of the areas around the solder
joint and, 5) consideration of design requirements and special conditions
affecting the joint, if any.
2
Visual inspection is an effective method for detecting
faults with solder joints. Low-power magnification is sometimes used to aid the
operation, especially with fine-pitch assemblies.*
1
I2.
incoming inspection
(
of materials and boards before
soldering connections) - The following characteristics are checked in incoming
components and bare circuit boards: 1) solderability, tested by a performance
test or conformance to materials and finish specifications, 2) finish of
component and board terminal surfaces to resist tarnish, 3) confirmation that
components will be able to withstand the heat of soldering, 4) resistance of
the boards and components to the cleaning materials to be used, 5) adequacy of
packaging, 6) quality of plating of conductive and terminal surfaces, 7)
whether the condition of board coatings is proper, 8) correctness of dimensions
of boards, traces, holes, leads, pads, etc. 9) cleanliness of terminal
surfaces. Soldering fluxes are checked for specific gravity or density, color
and clarity, ionic content and for the specified chemical analysis.
I3.
solderability testing
- is performed by dip soldering
the joint area, after proper fluxing, of the component to be tested. This step
is followed by a careful visual inspection of the joint area to verify that it
has been properly wetted. Sometimes, it is desirable to perform such a test
with a weaker flux than will be used in production so that, if the condition of
the component is marginal, the problem will be detected. Instruments are
available that facilitate the testing operation. One such instrument, called a
wetting balance, measures the flotation of a sample joint immersed in molten
solder. As wetting of the joint proceeds, its flotation decreases. Measurement
of this effect over a time span gives worthwhile data on the solderability of
the surface tested.
* Many inspection details are covered in the IPC 610-C
standard. (IPC, Northbrook, IL, www.IPC.org.)