Electrolytic Nickel-Phosphorous Reel-to-Reel Plating for
Aluminum Wire Bonding Applications
06/13/2011
INTRODUCTION
by Vince Azzano
Download as PDF
Aluminum wire bonding is used extensively in the electronics
industry as an interconnection in hybrid integrated circuits and
automotive sensor applications. These types of aluminum wire bonds
can be commonly found in fuel injection modules, anti-lock brake
modules, transmission control modules and air-flow sensors.
In these applications ultrasonic aluminum wire wedge bonds are
typically used to connect the sensor die or hybrid circuit to a
lead frame produced from a metal substrate. In the past these
metallic lead frames have been inlayed with aluminum in the area
intended for bonding. While aluminum inlayed surfaces provided a
highly reliable surface for aluminum wire bond applications the
high cost of using inlayed material has forced engineers to look
for more cost effective alternatives.
Electrolytic plated nickel sulfamate has shown to be a reliable
alternative to aluminum inlay in these aluminum wire bond
applications; however, unprotected nickel surfaces will slowly
oxidize resulting in wire bonding problems. To combat this
oxidation engineers have developed specifications calling for a
thin coating of precious metal or electroless nickel-phosphorous.
On the precious metal front, the use of electrolytic gold plating
has been shown to exhibit reliability issues when used in these
applications. These problems may be related to the rapid formation
of aluminum-gold intermetallics and the potential for Kirkendall
voids; however, more study would be necessary to identify the
source of these reliability issues. Electroplated palladium has
been shown to be a much more reliable choice in these applications
and it has the added advantage of being more cost effective than
gold. Thin layers of electroplated palladium over nickel sulfamate
have been used for over a decade in aluminum wire bonding
applications and have a proven history of reliability.
For lead frames that can be rack or barrel plated overall, a
thin layer of electroless nickel-phosphorous, over electrolytic
nickel sulfamate has also been proven to be a reliable alternative
to aluminum inlay. However, because electroless nickel-phosphorous
has a relatively slow deposition rate it has not been practical or
cost effective in reel-to-reel plating applications.
Recent developments in nickel-phosphorus plating chemistry have
provided a deposit that can be applied in an electrolytic system.
This chemistry allows for a faster deposition rate than its
electroless cousin and in reel-to-reel applications can be applied
selectively on either continuous coils of flat stock material or on
pre-stamped reel-to-reel lead frames.
Recently, Precision Plating put this new electrolytic
nickel-phosphorous chemistry to the test by conducting a design of
experiments that compared the aluminum wire bondability of this new
electrolytic nickel-phosphorous finish side-by-side with proven
palladium and electroless nickel-phosphorous coatings.
DESIGN OF EXPERIMENTS TEST MATRIX
For our DOE we plated five groups of samples;
SAMPLE GROUP #1 5-9 u" PALLADIUM
SAMPLE GROUP #2 5-9 u" ELECTROLYTIC NICKEL PHOSPHORUS
SAMPLE GROUP #3 10-14 u" ELECTROLYTIC NICKEL PHOSPHORUS
SAMPLE GROUP #4 5-9 u" ELECTROLESS NICKEL PHOSPHORUS
SAMPLE GROUP #5 10-14 u" ELECTROLESS NICKEL PHOSPHORUS
Each sample group was plated over a commonly used 260 brass lead
frame material and each sample was under-plated with a 50 u” layer
of electrolytic nickel-sulfamate. Additionally, each sample was
broken into two additional groups with one group aged by baking the
samples at 250 F for three hours. The baked samples were designed
to test the top coating’s ability to protect the underlying
nickel-sulfamate layer from oxidation. All of the groups were then
tested by an outside third-party test laboratory by wedge bonding
and pull testing 30 wire bonds using 0.010” aluminum wire.
Loading...
No selection was clipped for this page.
In our continuing tradition of rounding up new mobile
application releases we found interesting and/or exciting over the
past month, we present you with this new list of apps for June
2011. Previously in June, 
