Surface Spectroscopy
Objective
The objective is to provide an affordable rapid and nondestructive
assessment of the solderability of printed wiring boards (PWBs)
coated with organic solderability preservative (OSP). Surface
characteristics, such as oxide structure and quantity, have a
direct link to the ability of the surface to wet molten solder
(solderability).
Benefits
Real-time, nondestructive, rapid solderability measurements of
components and materials are currently not available to the electronics
industry. The inability to rapidly troubleshoot solderability
problems also causes significant cycle-time delays when problems
arise. Finally, with the miniaturization of electronics and use
of organic and organometallic preservatives, the ability to measure
the solderability of both high density components and coated board
metallization becomes nearly impossible.
Applicable Weapon Systems
This technology will be applicable to numerous weapon systems.
Initial demonstration vehicles include the HARM missile, MK86/UYK-7
Navy Computer, JDAM, and the Precision Lightweight GPS Receiver
(PLGR). In addition, there are numerous commercial applications
for this technology.
Technical Approach
First, a variety of surface reflectance spectrographic methods
were evaluated, including ellipsometry; infrared and near infrared;
Raman; ultraviolet and visible. The results were compared on the
basis of utility, ease of use and affordability. The most advantageous
system utilized UV-visible spectroscopy.
Next, using a prototype reflectance spectrophotometer
constructed from commercial off-the-shelf (COTS) components, the
reflectance properties of virgin and variously aged (oxidized)
copper samples were recorded and compared to the results of other
accepted measurements of solderability. At the same time, software
was developed to automate the spectral interpretation and translate
the result into useable data for assessing substrate solderability.
The value of this effort to PWB manufacturers was
presented at an IPC conference on surface finiishes and PWB solderability
Reflectance spectroscopy compares the light reflected
from the substrate to the reflected light from a reference standard.
Superimposed reflectance UV spectra from an aging
study of OSP-coated copper
