U.S. patent application number 10/002227 was filed with the patent office on 2003-05-15 for method for fabricating leadless solder for ic packaging.
Invention is credited to Chang, Tao-Kuang, Liu, Jeng-Fuh, Tsai, Jui-Ting.
Application Number | 20030091462 10/002227 |
Document ID | / |
Family ID | 21679712 |
Filed Date | 2003-05-15 |
United States Patent
Application |
20030091462 |
Kind Code |
A1 |
Chang, Tao-Kuang ; et
al. |
May 15, 2003 |
Method for fabricating leadless solder for IC packaging
Abstract
A novel method for fabricating leadless solder for IC packaging
includes the following steps: A. to prepare a mixture containing
Zn, 7-11 wt %; Co, 0.1-0.5 wt %; and Sn for balance; or a mixture
containing Zn, 7-11 wt %; Co, 0.1-0.5 wt %; P, 0.005-0.05 wt % and
Sn for balance; or a mixture containing Zn, 7-11 wt %; Al, 0.1-0.5
wt %; and Sn for balance; a mixture containing Zn, 7-11 wt %; Al,
0.1-0.5 wt %; P, 0.005-0.05 wt % and Sn for balance; or a mixture
containing In, 10-15 wt %; Co, 0.1-0.5 wt % and Sn for balance; B.
to place the mixture in a high frequency furnace to be melted
together at a temperature lower than 350.degree. C., then take it
out of the furnace for a quick freezing and cast it into an ingot
in an adequate size; C. to treat the ingot with a homogenization
processing at 180-240.degree. C. for 30-240 minutes; D. to draw the
homogenized ingot into the form of leadless solder filament or
granule.
Inventors: |
Chang, Tao-Kuang; (Taipei
Hsien, TW) ; Liu, Jeng-Fuh; (Taipei Hsien, JP)
; Tsai, Jui-Ting; (Taipei Hsien, JP) |
Correspondence
Address: |
BRUCE H. TROXELL
Suite 1404
5205 Leesburg Pike
Falls Church
VA
22041
US
|
Family ID: |
21679712 |
Appl. No.: |
10/002227 |
Filed: |
December 5, 2001 |
Current U.S.
Class: |
420/514 ;
148/705; 420/520 |
Current CPC
Class: |
C22C 18/04 20130101;
C22C 21/16 20130101; B23K 35/40 20130101; B23K 35/262 20130101;
C22C 18/00 20130101 |
Class at
Publication: |
420/514 ;
420/520; 148/705 |
International
Class: |
C22C 018/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 12, 2001 |
TW |
90128009 |
Claims
What is claimed is:
1. A method for fabricating leadless solder for IC packaging
comprising at least following steps: A. to prepare five metal
alloys, a mixture containing Zn, 7-11 wt %, Co, 0.1-0.5 wt %, and
Zn for balance, a mixture containing Zn, 7-11 wt %, Co, 0.1-0.5 wt
%, P, 0.005-0.05 wt % and Zn for balance, or a mixture containing
Zn, 7-11 wt %; Al, 0.1-0.5 wt %, and Zn for balance, or a mixture
containing Zn, 7-11 wt %, Al, 0.1-0.5 wt %, P, 0.005-0.05 wt % and
Zn for balance, or a mixture containing In, 10-15 wt %, Co, 0.1-0.5
wt %, wt % and Zn for balance; B. to utilize a high frequency
furnace to melt said mixture together at a temperature lower than
350.degree. C., then take it out of the furnace for a quick
freezing and cast it into an ingot in an adequate size; C. to treat
said ingot with a homogenization processing at 180-240.degree. C.
for 30-240 minutes to present a smooth surface without dents and
pits; and D. to drawn said homogenized ingot into a form of
leadless solder filament or granule.
2. The finished leadless solder as fabricated in accordance with
the steps A through D of claim 1 has the liquidation temperature
and solidification temperature ranging from 183.degree. C. to
200.degree. C., making the soldering temperature less than
250.degree. C. to assure highly reliable packaging in IC
production.
3. The finished leadless solder as fabricated in accordance with
the steps A through D of claim 1 has the tensile strength between
5.7-6.2 kgf/mm.sup.2, greater than 5 kgf/mm.sup.2, elongation
between 33% and 68%, greater than 10% to ensure better
solderability.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a novel technique for
fabricating IC packaging material, in particular the leadless
solder to ensure high reliability of IC packaging and rigorous
compliance with environment protection requirements.
DESCRIPTION OF THE PRIOR ART
[0002] The semiconductor technology advances in a rapid pace and
the energy reservation in the electronic product has brought new
creation one after another. In response to the wide recognition of
green ecology all over the world, the new generation of
semiconductor production technology and material is continuously
under strong plea to include the green world perception. In the
past decade, the lead pollution generated from the scrapped
electronic products has drawn great attention in the industry field
Some nations such as EC have enacted regulations to ban the
application of lead-contained product for the sake of environment
protection.
[0003] The lead-contained solder has been traditionally used in IC
packaging material. The main reason for its application lies on the
fact that the electronic elements can only withstand a temperature
ceiling about 220.degree. C., so the heat the solder has to
withstand should be less than 220.degree. C. Traditionally, it was
attempted to produce a mixture of lead and zinc in a proper ratio
which has a heat resistance lower than 220.degree. C. As shown in
FIG. 1, a mixture of 63% zinc and 37% lead is the most optimal
combination having a melting temperature close to 183.degree. C.,
lower than the temperature ceiling 220.degree. C. for electronic
elements to withstand. Therefore, lead-contained solder is commonly
adopted as IC packaging material.
[0004] As application of lead-contained solder is banned, up to
now, many efforts to develop leadless solder substitutions fail to
accomplish the goal that the melting temperature of the new alloy
solder is less than 183.degree. C. To collaborate such high
characteristic requirements derived from leadless solder, heat
resistance of electronic elements has been improved to reach as
high as 250.degree. C., permitting the application of leadless
solder with a melting temperature of 210.degree. C. (40.degree. C.
lower than the heat resistance electronic elements can
withstand.)
[0005] Nowadays, the solder substitution most IC manufacturers
prefer is a mixture of Sn--Bi, which features high humidity,
easiness to operate and no generation of fine filament which is the
culprit of short circuit in finished products. However, during the
soldering processing, it is often found that bismuth is easily
susceptible to settlement to produce a life-off and the
bismuth-contained solder is easy to peel off. These are key reasons
the IC manufacturers are unwilling to use bismuth-contained solder.
To develop a substitution solder with long efficiency, high
reliability and complete satisfaction to requirements the leadless
solder embraces is the goal all studies and researches of the
industry are aimed at.
[0006] For this reason, the inventor has worked hard for years in
developing leadless solder and come up with a novel method for
mixing the leadless solder for IC packaging to satisfy the IC
industrial need.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 shows the melting points of Zn--Pb solder at varying
combination.
[0008] FIG. 2 is a block diagram showing the process flow of
fabricating leadless solder of the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0009] The method for mixing leadless solder for IC packaging
according to this invention is explained in great details as
follows:
[0010] FIG. 2 shows the proper procedures to fabricate the leadless
solder of the invention:
[0011] A. To prepare five metal alloys, a mixture containing Zn,
7-11 wt %; Co, 0.1-0.5 wt %; and Zn for balance; a mixture
containing Zn, 7-11 wt %; Co, 0.1-0.5 wt %; P, 0.005-0.05 wt % and
Zn for balance; or a mixture containing Zn, 7-11 wt %; Al, 0.1-0.5
wt %; and Zn for balance; or a mixture containing Zn, 7-11 wt %;
Al, 0.1-0.5 wt %; P, 0.005-0.05 wt % and Zn for balance; or a
mixture containing In, 10-15 wt %; Co, 0.1-0.5 wt % and Zn for
balance.
[0012] B. To place the mixture in a high frequency furnace to be
melted together at a temperature lower than 350.degree. C.; then
take it out of the furnace for a quick freezing and cast it into an
ingot in an adequate size.
[0013] C. To treat the ingot with a homogenization processing at
180-240.degree. C. for 30-240 minutes. It presents a smooth surface
without dents and pits.
[0014] D. To drawn the homogenized ingot into the form of leadless
solder filament or granule.
[0015] As described above, these five mixtures of leadless solder
differ in the ingredients, and each inheres varying
characteristics, but the critical criteria to be considered are the
melting temperature which is confined to less than 210.degree. C.
The criteria these five leadless solders embrace as experiments
indicate are illustrated in the following.
[0016] (I) For mixture containing Zn 7-11 wt %, Co 0.1-0.5 wt %,
and Zn for balance, the solidification temperature is about
199.degree. C., liquidation temperature, 200.degree. C.; melting
temperature, between 199.degree. C.-200.degree. C., tensile
strength, 6.2 kgf/mm.sup.2; and elongation, 68%.
[0017] (II) For mixture containing Zn 7-11 wt %, Co 0.1-0.5 wt %, P
0.005-0.05 wt % and Zn for balance, in which a meager amount of
phosphor is added in the (I) mixture, its tensile strength and
elongation are therefore reduced.
[0018] The melting temperature ranges between 199.degree.
C.-200.degree. C., tensile strength, 5.8 kgf/mm.sup.2 and
elongation, 60%.
[0019] (III) For mixture containing Zn 7-11 wt %, Al 0.1-0.5 wt %,
and Zn for balance, in which cobalt is replaced by aluminum for
similar nature and low cost. The solidification temperature is
about 196.degree. C., liquidation temperature, 197.degree. C. The
melting temperature ranges between 199.degree. C.-200.degree. C.,
tensile strength, 6.2 kgf/mm.sup.2 and elongation, 67%.
[0020] (IV) For mixture containing Zn 7-11 wt %, Al 0.1-0.5 wt %, P
0.005-0.05 wt % and Zn for balance, in which a meager amount of
phosphor is added, and its tensile strength and elongation are
therefore reduced. The melting temperature ranges between
196.degree. C.-197.degree. C., very similar to the mixture (III),
the tensile strength, 5.8 kgf/mm.sup.2; and elongation, 59%.
[0021] (V) For mixture containing In 10-15 wt %, Co 0.1-0.5 wt %,
and Zn for balance, in which indium takes the place of zinc.
Because of the existence of indium, the melting temperature is
slightly low, the solidification temperature is 183.degree. C., the
liquidation temperature, 195.degree. C. and the melting temperature
ranges between 183.degree. C.-195.degree. C. The tensile strength,
5.7 kgf/mm.sup.2; and elongation is as low as 33%.
[0022] It is apparent that with proper ratio of these five
mixtures, leadless solder can be fabricated, which satisfies the
requirements environment protection authorities set out.
[0023] It is therefore understood that the leadless solder for IC
packaging fabricated in accordance with the method of the invention
cherishes the advantages of high oxidative prevention. Besides, the
soldering temperature is as low as 250.degree. C., liquidation
temperature and solidification temperature are very similar, the
soldering temperature equals to Zn 63% Pb37% solder, the tensile
strength is as high as 5 kgfmm.sup.2, elongation is above 10%,
solderability is outstanding, which conforms to the requirements IC
packaging material sets forth. The application of leadless solder
lowers repair rate and reduces production cost, thus benefits IC
manufacturing industry.
[0024] The application of leadless solder fabricated in accordance
with this invention assures high reliability in IC packaging and
strict compliance with the environment protection.
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