Lead-free solders in Japan (a personal impression)
W.J. Plumbridge
Department of Materials Engineering, The Open University, Milton Keynes, UK
Introduction
The introduction of lead-free solders is being driven by the
anticipated legislation for the abolition of toxic lead from
electrical and electronic goods, and the perceived
commercial benefits of marketing lead-free mobile phones,
computers and the like. While Europe and Japan are under
greater pressure from the environmental lobby than the
USA, the potential commercial advantages have heightened
interest universally in this topic.
The author has been awarded support from the British
Council Collaborative Research Fund for three annual visits
to Japan to carry out a specific joint research project with
Professor M. Sakane of Ritsumeikan University, and to
monitor the situation in Japan on this extremely important
aspect. In 1998, attention was focussed upon activities in
Japanese universities and this year the emphasis was on
industry. The present article attempts to construct an
overview of the current situation in Japan. At the outset,
several caveats must be cited. First, the report is restricted
to those institutions visited, or closely associated with them.
These were selected with guidance from Japanese
colleagues and on the basis of availability. An element of
randomness is inevitable in this respect. Second, there is the
bias dictated by the author's interests and expertise, which
may be described as ``mechanical behaviour of solders, a
growing association with mechanical behaviour of soldered
joints and an awareness of board performance during
service and thermal cycling''. In other words, the
production of a sound joint is assumed and the subsequent
performance is the principal focus.
Rather than simply describing a sequence of visits, the
article attempts to brigade topics together to improve
cohesion. In essence, many of the technical areas
considered are interrelated, and are necessary components
of the pursuit of reliable lead-free solder interconnections.
Initially, the national scene in Japan is considered together
with the stated objectives of major electronics companies.
Subsequently, progress on specific technical challenges,
such as life prediction and the difficulties arising from the
higher melting point of lead-free solders, are reviewed.
The national scene
The ``big picture'' regarding the overall situation in Japan
with regard to the introduction of lead-free solders emerged
mainly from discussions with staff from Rohm and with
Professor Sakane. While individual companies have their
own specific targets (Table I) they also collaborate via the
Electronic Industries Association of Japan. This
organisation has a Lead-Free National Project under way
and intends to produce a final report in April 2000. The
Rohm Company has had a Lead-Free Promotion Committee
in place for two years with the objective of facilitating the
adoption of lead-free solders by its customers. It aims for
quantity production of devices by the start of 2001. Rohm,
with ten researchers allocated to the lead-free challenge, is
presently examining tin-silver, tin-bismuth alloys for
plating and tin-copper, tin-silver-copper, tin-silver-copper-
bismuth for solder dips. The tin-bismuth alloys have
presented difficulties in automobile applications due to
fillet lifting.
There are three other relevant committees focusing on
lead-free solders:
1 Microsoldering Committee ± (chaired by Professor
Takamoto in Osaka) focuses on metallurgical aspects.
2 Committee RC128 of JSME (Japanese Society for
Mechanical Engineering) ± (chaired by Professor
Shiratori) is concerned with finite element analysis of
Joints.
3 The Solder Committee of JSMS (Japanese Society for
Materials Science) ± (chaired by Professor Sakane)
concentrates on standardisation of testing methods,
especially for tensile and low cycle fatigue properties.
This last committee is just completing a multi-laboratory
exercise on tin-lead and tin-silver alloys and an extensive
database will be published in the near future. Many
Japanese test programmes employ pre-aged specimens,
which may produce different results from the as-cast
condition. The treatment used by the members of the Solder
Committee is for stabilisation and involves ageing at 1008C
for one hour.
A company aim of Matsushita (also known as National
or Panasonic) is to be the first in the world to use absolutely
no lead for the connecting material and component
electrodes on electronic circuit boards. They have well-
defined plans for achieving this goal within two years, in at
least four major products. They have successfully
introduced tin-silver in the mass production of the mini disc
player and tin-copper for PCB boards in VTR systems.
Their policy seems to be to utilise existing lead-free alloys
and to test final components rather than become involved
with basic design. They are using all the ``popular'' lead-
free alloys with the inclusion of tin-antimony and tin-zinc
for lower temperature applications. There is still concern
about the high melting points of lead-free solders and the
temperature variations that may exist around the board due
to differences in thermal capacity of components. In
addition to amelioration by complex heating systems, the
company is still seeking new lead-free alloys with lower
melting points. While no drop-in replacement for tin-lead
eutectic is likely to emerge, they consider that the alloys
available are adequate, and it is now a matter of
implementation of lead-free solders as quickly as possible.
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[ 32 ]
Soldering & Surface Mount
Technology
12/1 [
2000
] 32±34
# MCB University Press
[
ISSN 0954-0911
]
Keywords
Lead-free soldering, Japan,
Abstract
Impressions gained from two visits
to Japan, discussing with
representatives of industry and
academe the current status
regarding the implementation of
lead-free technology, are
presented. Driven by the
commercial rewards of lead-free
goods, Japan appears to have
more clearly articulated targets
for the removal of lead, in advance
of the expected timescales in EU
legislation. Various strategies for
combating problems associated
with the higher melting point of
lead-free solder alloys have been
investigated. Design and
development generally involve a
broader approach than in Europe,
involving stress analysis,
materials properties and life
prediction to underpin empirical
data obtained by thermal cycling
of boards. Despite the existence
of several committees to facilitate
the introduction of lead-free
solders, a lack of cohesion is
sometimes apparent, particularly
regarding heat treatment of
materials prior to testing. It is
proposed that a challenge as
demanding as this would benefit
from greater collaboration
internationally.
Received: August 1999
Revised: September 1999