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Silver-free AMB and copper bonding for cost-efficient,

reliable advanced packaging

By A. Schwöbel, C. Féry, B. Fabian, D. Schnee, M. Rauer, A. Miric, S. Gunst [Heraeus Deutschland GmbH & Co. KG]
H igh-power electronics have are the major price drivers for AMB conducted. Results of the experiments

become one of the fastest
R e g a r d i n g t h e a t t a c h m e n t of
design-to-cost, highly-reliable Ag-
growing market segments subst rates. We have developed a follow in the first part of this article.
of the semiconductor industry. Major f r e e t h ick-f i l m c o p p e r b ond i ng dies to metal ceramic substrates,
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applications include motor drives, (Condu r a .u lt r a) t e ch nolog y for a clear trend is the replacement of
hybrid/electric vehicles, rail traction, joining nitride-based ceramics with conventional soldering with silver
w i nd t u rbi nes, a nd photovolt aic Cu foils. The paste eliminates the pressure sintering when higher power
inverters. Because the power electronic use of an expensive vacuum-based densities are required. With a melting
modules used in these applications brazing technology. But how does temperat ure of 961°C, a sintered
operate at high voltage and high this new bonding technology perform silver bonding layer enables operating
current density, they must handle high compared to the industry-benchmark temperatures above 200°C, whereas a
temperatures and harsh conditions. A M B subst rate? To compare the lead-free soldered joint, with a melting
One of the key components for highly performance between the two kinds temperature of about 230°C, quickly
reliable power electronic modules is of substrates, various re-liability- deg rades. Fu r ther more, the heat
a reliable metal ceramic substrate. To and application-related tests such transport through the joining layer is
provide reliable functionality during as thermal shock (-65°C/+150°C), significantly better with Ag sintering
operation, the substrate materials peel strength, and high-temperature rather than with soldering (>200W/m/
must provide outstanding electrical, storage (175°C, 1,000 hours) were K against <65W/m/K) (Figure 1) [4].
thermal, insulation and mechanical
performance. Additionally, they must
work with commonly-used assembly
and interconnection technologies
like soldering, sintering, and wire
bonding. Another critical aspect is to
ensure a reliable die attachment and
interconnection that can transport
ever-increasing currents and efficiently
take away the generated heat.
Due to cost efficiency, Al 2 O 3 -based
metal ceramic substrates, i.e., direct
copper-bonded substrates, are often
used for power module manufacturing
[1]. However, Al 2 O 3 -based ceramics Figure 1: Temperature increase during operation for a die either a) sintered, or b) soldered on metal
cannot fully leverage the potential ceramic substrates.
of wide-band-gap semiconductors.
As a result, silicon nitride-based
metal ceramic substrates are gaining
popularity as materials for power
module assembly. Si 3 N 4 shows superior
mechanical properties combined with
high thermal conductivity [2].
H i g h ly r e l i a b l e S i 3 N 4 - b a s e d
substrates are typically manufactured
with active metal brazing (AMB)
technology that uses Ag-filled and
active metal (i.e., titanium) containing
brazing pastes [3]. The precious
metal content in the brazing paste Figure 2: a) Si-IGBT soldered on Al 2 O 3 -DCB and interconnected with Al wires; and b) SiC-MOSFET sintered
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and a slow vacuum brazing process on Si 3 N 4 -AMB with DTS . Substrate designs from IISB.
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