JP2002086294A - Electronic member having solder alloy, solder ball and solder bump - Google Patents

Abstract

(57) Abstract: An electronic member having a solder alloy, a solder ball, and a solder bump is provided with a solder alloy or the like which has improved fatigue resistance more than before and has excellent impact resistance. SOLUTION: Sn: 55 to 70% by mass, Ag: 0.5
To 5.0% by mass, Sb: 0.1 to 3.0% by mass, Bi:
0.1 to 3.0% by mass, Cu: 0.01 to 0.1% by mass
, The balance consisting of Pb and unavoidable impurities, and A
A solder alloy, a solder alloy used for a solder bump for an electronic member, and a solder ball for an electronic member, wherein the total content of g, Sb, Bi, and Cu is 5.0% by mass or less. Further F
e, one or two or more metals selected from the group consisting of Ni, Zn, In, Pt, and Pd in an amount of 0.01 to 0.5% by mass.
contains. Further, P: 0.0005 to 0.005% by mass
It contains. An electronic member having a solder bump and a solder electrode formed of the solder alloy.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic member having a solder alloy, a solder ball and a solder bump, and more particularly to an electronic member having an environment in which metal fatigue is likely to occur due to repeated stresses such as temperature cycling. And a solder alloy suitable for micro soldering of electronic components.

[0002]

2. Description of the Related Art Generally, when electronic components are mounted on a printed wiring board or the like, a Sn-Pb eutectic periphery (Sn: 63% -P
(b: 37%) is widely used, and similar solder components are mainly used in solder balls for BGA (Ball Grid Array), which are increasing rapidly in recent years. On a printed circuit board incorporated in an electronic device or an integrated circuit element substrate using a BGA, the device switch is turned on.
It is exposed to a thermal shock cycle environment in which heating and cooling are repeated with / OFF.

When a solder joint is exposed to a thermal shock cycle environment, a thermal stress is generated due to a difference in thermal expansion coefficient between an electronic component and a printed circuit board. In particular, in micro solder ball connection such as flip chip connection in which an integrated circuit chip is directly mounted on a substrate, since the Si chip element and the mounted printed wiring board are directly connected by solder balls, the difference in thermal expansion coefficient between the silicon chip and the printed wiring board is reduced. The resulting thermal stress is very large. This thermal stress is concentrated on the joint having a small cross-sectional area, and the strength of the solder material of the joint is weaker in material strength as compared with the other members to be joined. Cracks occur in the solder, resulting in fatigue failure.

Conventionally, a solder joint is likely to be broken by thermal stress by using a mounting form design in which component leads are bent and the thermal stress is relieved by the component, or an electrode pad at the joint is enlarged. That is, measures have been taken such as increasing the amount of solder at the joint to reduce the stress applied to the joint as a result.

Further, in order to improve the fatigue resistance of the solder material, the strength of the solder material has been conventionally improved by adding a third element to the Sn-Pb alloy. Japanese Patent Application Laid-Open No. 1-127 discloses a Sn-Pb alloy to which a third element is added.
192 and JP-A-1-12337095, etc.
b, In, Ag, Cu, Bi, Te, Ni, etc. are added to improve the fatigue resistance. In addition, various solder alloys have been proposed, but most of them include adding a third element to a Sn-Pb-based alloy to form an Sn phase and a Pb in the solder structure.
By precipitating intermetallic compounds at the grain boundaries of the phase, and by using this compound to suppress coarsening of crystal grains or to function as pinning pin sites for suppressing plastic deformation, the strength, creep resistance, and resistance of the alloy are improved. Attempts have been made to improve fatigue properties.

In JP-A-3-204194, an element selected from Cu, Ni, Au, Ag, Pt and the like is added to a PbSn substrate as an element which easily forms a compound with Sb and Sb, and an intermetallic compound is added. By forming crystal grain boundaries dispersed and precipitated, the thermal fatigue characteristics and creep resistance of the PbSn substrate are improved.

In Japanese Patent Application Laid-Open No. 7-178587, the fatigue characteristics are improved by adding Ag, Sb, and P to SnPb-based solder. Ag and Sb are added for the purpose of increasing the material strength of the solder, and P is used for improving the thermal fatigue characteristics of the solder. Cd, Bi, I
0.11% or more of a metal selected from n, Zn, Cu, and Ga is contained. Cd, Bi, and In are used for the purpose of lowering the melting point of the solder, and Zn and Cu are used for the purpose of improving the material strength.

[0008] JP-A-1-237095, JP-A-3-3
Japanese Patent No. 32487 discloses that PbSn-based solder has Sb
And In are added, and further, Ag and Cu are added thereto to improve the fatigue resistance. It is presumed that strengthening (improvement of tensile strength) by simultaneous addition of Sb and In is a cause of excellent fatigue resistance. Addition of Ag and Cu to this further improves the fatigue resistance. Ag, Cu
Is preferably 0.1% or more. In Japanese Patent Application Laid-Open No. 3-106591, the I
A PbSn-based solder having excellent fatigue resistance, including at least one of n and Ga, at least one of Sb and Bi, and at least two of Ag and Au is disclosed.

[0009]

With the recent high-density mounting of electronic components, notebook computers, video cameras,
In mobile phones and the like, surface mounting and BGA mounting have progressed, and the area of the substrate electrode pad has been rapidly reduced, so that the amount of solder at the joint site has to be reduced. That is, the joint area at the solder joint portion is reduced, and the stress applied to the joint is increasing. In addition, due to the high functionality and miniaturization due to the high-density mounting, the portability of information transmission equipment has also rapidly advanced. In addition, the scope of economic activity has reached the global scale,
Such devices have come to be used in scorching deserts and extreme cold conditions in polar highlands, which have not been considered before. Under such circumstances, there is a demand for a solder mounting design that takes into account the fact that the solder joint is exposed to a more severe environment, and thus the demand for improved fatigue resistance of the solder material has been further increased.

It is necessary to assume that a mobile phone is accidentally dropped on the floor during use due to its use characteristics.
It is required that the solder joint of the electronic component used has such an impact resistance as not to be destroyed even by such an impact. On the other hand, in the conventional fatigue-resistant solder alloy, the fatigue resistance is improved mainly by increasing the strength of the solder, and as a result, the impact resistance tends to decrease. .

[0011] Fatigue destruction of solder is caused by concentration of thermal stress in a connection portion on a solder material. That is, the connection portion has elastic plastic deformation capability and strength enough to maintain the connection, absorbs thermal stress, and reduces stress applied from the connected member. Dispersing and precipitating intermetallic compounds in the solder structure and at grain boundaries has some effect on suppressing grain boundary sliding and fracture cracking.However, when a certain amount or more of intermetallic compounds having brittle and hard properties is present. The spreadability of the solder is impaired, and the stress relaxation at the connection portion is reduced. A typical example of conventional fatigue-resistant solder is a Sn-Pb alloy to which a small amount of Ag is added as a third element, which precipitates Ag ₃ Sn intermetallic compound to suppress grain boundary slip and improve fatigue resistance. Have improved.

However, when a small amount of Ag is added as a third element to the Sn-Pb alloy, the strength is about 20% as compared with the Sn-Pb alloy eutectic composition (Sn63-Pb37).
Despite the increase, the elongation is reduced by about 20%, and the improvement in overall fatigue resistance is not so large. As a result of the reduced elongation, sufficient quality cannot be ensured for impact resistance. That is, a solder alloy having excellent fatigue resistance and impact resistance required for a BGA solder ball alloy used when mounting a CPU or an electronic component on a printed wiring board is used for holding the mounted component. It is a solder alloy that has both strength and ductility to reduce thermal stress and impact. Conventionally, Sn that satisfies such strength and ductility
-No Pb-based solder alloy was found.

SUMMARY OF THE INVENTION An object of the present invention is to provide a solder alloy and the like having improved fatigue resistance and improved impact resistance in an electronic member having a solder alloy, a solder ball and a solder bump. .

[0014]

According to the present invention, Sn is used.
Was added to Ag in -Pb alloy, Ag ₃ Sn intermetallic compound is finely dispersed in the crystal to improve the fatigue resistance.

Sn has the property of transforming at 13.2 ° C. In a Sn-Pb-based alloy, Sn
During transformation, rupture is apt to progress significantly, resulting in destruction of the solder electrode joint. TCT test (e.g., -4) used to evaluate the thermal fatigue properties of solder electrode joints
(A repetition of a heating / cooling cycle of 0 ° C. to 125 ° C.), when exposed to a low temperature, the breakage of the solder electrode joint part progresses, and eventually leads to destruction. The present invention relates to the addition of Ag to Ag.
By further adding Sb to the n-Pb-based solder alloy, Sn transformation at low temperatures can be suppressed, and heat-resistant fatigue characteristics that can sufficiently withstand even in cold regions are realized.

The present invention relates to Sn—P containing Ag and Sb.
By adding appropriate amounts of Cu and Bi to the b-based alloy, the fatigue resistance was further improved without impairing the ductility of the solder alloy, and at the same time, the impact resistance was improved.

Conventionally, when Cu is added to a fatigue-resistant solder alloy, 0.1% is added to improve the strength of the alloy.
The above Cu was contained. The present inventor has set Cu to 0.1.
It has been found that when the content is 1% or more, the strength is improved but the ductility is reduced. And, when the content of Cu is 0.1
%, Most preferably about 0.05%, it is possible to obtain an alloy having excellent ductility while obtaining the effect of improving the strength of the solder alloy. Further, Bi was solely and sufficiently dissolved in Pb, and by setting the Bi content to 3% or less, the strength could be improved without impairing the ductility of the solder alloy.

The elongation of the Sn-Pb-based solder alloy exhibits almost the maximum value in the eutectic component, but when the eutectic component contains another element, the elongation of the alloy decreases. On the other hand, particularly in the component system of the present invention, by controlling the total content of other components contained in the Sn-Pb-based alloy to 5% or less,
The ductility of the alloy could be secured.

That is, the gist of the present invention is as follows. (1) Sn: 55 to 70% by mass, Ag: 0.5 to 5.0
Mass%, Sb: 0.1 to 3.0 mass%, Bi: 0.1 to
3.0% by mass, Cu: 0.01 to 0.1% by mass,
The balance is composed of Pb and unavoidable impurities, and Ag, Sb,
A solder alloy, wherein the total content of Bi and Cu is 5.0% by mass or less. (2) The composition as described above, further comprising a total of 0.01 to 0.5% by mass of one or more metals selected from the group consisting of Fe, Ni, Zn, In, Pt, and Pd. The solder alloy according to (1). (3) The solder alloy according to the above (1) or (2), further containing P: 0.0005 to 0.005% by mass. (4) The solder alloy according to any one of the above (1) to (3), which is used for a solder bump for an electronic member. (5) A solder ball for an electronic member, comprising the solder alloy according to any one of (1) to (3). (6) An electronic member having solder bumps, wherein a part or all of the solder bumps are formed of the solder alloy according to any one of the above (1) to (3). . (7) An electronic member in which a plurality of electronic components are joined by a solder electrode, and a part or all of the solder electrode is formed of the solder alloy according to any one of (1) to (3). An electronic member characterized by the above-mentioned.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION The solder alloy of the present invention takes into account the lack of ductility which is inversely proportional to the strength improvement, which was a weak point of the conventional fatigue-resistant solder in which an intermetallic compound is precipitated in the solidified structure of the solder. It was done. That is, in the liquid state, it melts uniformly, in the solid state, there is no excessive precipitation of intermetallic compounds in the solidified structure, and the solder alloy itself has sufficient strength to hold the mounted component with a small amount of solder. And Sn-P for ductility to reduce thermal stress and impact
It is a solder alloy having excellent fatigue resistance and impact resistance, having a ductility equal to or higher than the eutectic composition of the b-based alloy.

When Sn is alloyed with Pb, the eutectic point (S
n: 63% by mass), and the eutectic temperature (18
3 ° C). In order for the solder alloy of the present invention to be a component suitable for bonding with a BGA solder ball or the like used when mounting a CPU or electronic components on a printed wiring board, S
n: 55 to 70% by mass.

When Ag is added to the Sn—Pb solder alloy,
At the time of solder solidification, an intermetallic compound such as Ag ₃ Sn is finely precipitated at a crystal grain boundary or the like, thereby suppressing the coarsening of Pb and improving fatigue resistance. In the Sn-Pb solder alloy, the addition of less than 0.5% by mass does not show remarkable improvement in fatigue resistance, and the addition of 5% by mass or more increases the liquidus temperature,
It is not suitable for BGA solder used when mounting a CPU or electronic components on a printed wiring board. From an economic viewpoint, it is desirable that the Ag content be 2.5% by mass or less.

As described above, the present invention relates to a method for preparing Ag-containing S
By further containing Sb in the n-Pb-based solder alloy, Sn transformation at a low temperature can be suppressed. S
If the b content is less than 0.2% by mass, the effect of suppressing the low-temperature transformation of Sn is not sufficient, so the lower limit is set to 0.2% by mass. If the content exceeds 3.0% by mass, the wettability of the solder starts to decrease. Therefore, the upper limit is set to 3.0% by mass.

In addition to the improvement in the fatigue resistance of the solder alloy as described above, in the present invention, the thermal cycle impact test (TCT evaluation) in the board-to-board solder joints has shown that the conventional 1000 cycle durability was difficult. In order to improve the reliability and the practicality while improving the reliability in flip-chip connection in which a silicon chip is directly connected to a substrate in semiconductor element mounting, and to improve impact resistance, Cu
And Bi are added in appropriate amounts.

Cu improves the strength of the solder alloy and improves the fatigue resistance. In a conventional fatigue-resistant solder alloy, Cu
In order to obtain the effect of improving the strength, it is said that it is preferable to contain Cu in an amount of 0.1% or more. However, 0.
It has been clarified that when Cu exceeds 1%, the strength is improved but the ductility of the solder alloy is reduced. In the present invention, by setting the upper limit of the Cu content to 0.1% by mass, the strength is improved without impairing the ductility of the solder alloy, and the fatigue resistance and impact resistance of the solder alloy are significantly improved. The point has the biggest feature. In order to obtain the effect by the Cu content, the lower limit of the Cu content is set to 0.01% by mass. C
The upper limit of the u content is more preferably 0.07% by mass and the lower limit is 0.03% by mass. The most favorable results are obtained with a Cu content of about 0.05% by mass.

In the present invention, Bi is added to the solder alloy in order to improve the strength without impairing the ductility. Bi is solely sufficiently dissolved in Pb, and the mechanical properties can be improved by adding a small amount of Bi. In order to obtain the effect of adding Bi, it is necessary to contain 0.1% by mass or more.
On the other hand, if the Bi content exceeds 3.0% by mass, the solder alloy becomes brittle, so the upper limit is set to 3.0% by mass. A more preferable range of Bi for improving the mechanical strength of the solder alloy and not impairing the ductility is 0.1 to 1.0% by mass.

The Sn-Pb solder alloy has the maximum elongation in the eutectic component. The inclusion of other elements in the eutectic component affects the elongation of the solder alloy, particularly in the component system of the present invention. In the present invention, A
By setting the total content of g, Sb, Bi, and Cu to 5.0% by mass or less, good ductility can be ensured. If the total content of these components exceeds 5.0% by mass, the ductility of the solder alloy is significantly reduced.

In the above (2) of the present invention, Fe, Ni, Zn, In, Pt,
One or more metals selected from the group consisting of Pd are contained in a total amount of 0.01 to 0.5% by mass. When these components are contained, a fine intermetallic compound with Sn and / or Sb is formed and finely dispersed in the solder, thereby contributing to the suppression of coarsening of Pb. However, if the content exceeds 0.5% by mass, the ductility of the solder alloy decreases, so the upper limit of the content was set to 0.5% by mass. Further, when the content of the alloy element was less than 0.05% by mass, no clear difference was observed from the case where the element was not contained. Therefore, the lower limit of the content was 0.05% by mass.

In the above (3) of the present invention, P: 0.0005 to 0.0 is added to the above (1) and (2).
Contains 0.05% by mass. When P is contained, it is effective in improving the wettability of the solder, and the wettability is improved by adding 0.0005% by mass or more of P. Further, when P is added in excess of 0.005% by mass, the solder alloy material becomes hard, and the TCT evaluation material,
In applications where ductility is required, such as impact resistance materials, the material properties are not exhibited.
The content was 5% by mass.

As described in detail above, the solder alloy of the present invention has a high material strength and is particularly excellent in fatigue resistance and impact resistance. Therefore, the solder alloy of the present invention is used as a solder bump for electronic members. When used, favorable results can be obtained.

The solder ball (5) of the present invention is suitable as a solder ball for forming a solder bump.
On the electrodes formed on the surface of the electronic member, adhere the solder ball of the present invention via a flux or solder paste,
Next, the solder is melted and reflowed by heating to a high temperature, so that a solder bump is formed on the electrode on the surface of the electronic member.

The above (6) of the present invention is an electronic member having a solder bump formed of the solder alloy of the present invention.
As means for forming a solder bump, it is preferable to form the solder bump on an electronic member using the solder ball of the present invention (5).

When a solder paste is used to form the solder bumps, the solder bumps after the reflow are formed by melting and mixing the solder balls and the solder components in the solder paste. At the time of reflow, the solder paste used may contain a solder alloy containing a large amount of Ag, Sb, Bi, Cu, and other solder alloy components of the present invention in the paste. In some cases, Sn-Pb eutectic solder containing no element is used.
Therefore, the content of the additive element contained in the solder ball, after the solder and the solder ball in the paste are mixed, the components of the paste used, so that the additive element content is within the optimal component range in the solder alloy of the present invention. It is preferable to adjust the concentration of the additive component according to the amount and the amount used.

In an electronic member in which a plurality of electronic components are joined by solder electrodes, such as flip chip joining,
As described in the above (7) of the present invention, a part or all of the solder electrode is formed of the solder alloy of the present invention. At the time of joining, first, a solder bump is formed by a solder alloy of the present invention on a flat electrode on the surface of each electronic component to be joined (the present invention (6)). Next, solder bumps 2 were formed.
By facing the two electronic components and bringing the solder bumps on the electrodes to be joined into contact with each other and heating them to a high temperature, both solder bumps melt and reflow, and the joints between the facing electronic components are joined by the solder electrodes. It will be joined. Since the solder electrodes are joined by the solder alloy of the present invention, the solder electrodes at the joining portions have high strength and are particularly excellent in fatigue resistance and impact resistance.

[0035]

EXAMPLES Example 1 Evaluation of Thermal Fatigue Properties A 300 μm diameter solder ball having the components shown in Table 1 was manufactured, and this solder ball was adhered to an electrode on the substrate surface via a solder paste. Reflow solder bumps were obtained. The number of electrodes on the substrate is 240. The same glass epoxy resin substrate (1 cm square) as the glass epoxy resin substrate (4 cm square) was used as the substrate. The two substrates were flip-chip bonded by facing each other, contacting both solder bumps, and melting and reflowing. Next, a thermal shock cycle test was performed on the flip-chip bonded electronic member. Thermal shock cycle test (TCT evaluation)
Is subjected to a thermal cycle of −40 ° C. to 125 ° C.
Those which did not cause breakage until the cycle were judged as acceptable.
The thermal cycle was further performed up to 2000 cycles, and the change in the rate of breakage was investigated.

In Table 1, Examples 1 to 4 of the present invention are Examples of the present invention. Comparative Example 1 was a Sn-Pb eutectic alloy, and Comparative Example 2 was A
The g-containing Sn-Pb eutectic alloy, Comparative Example 3 is an example in which the content of Cu is outside the range of the present invention, and the Cu content is outside the range of the present invention.

[0037]

[Table 1]

[0038]

[Table 2]

Table 2 shows the results of the rate of occurrence of breakage. In each of Inventive Examples 1 to 4, no break occurred in 1000 cycles, and good results could be obtained. In contrast, in each of the comparative examples, breakage occurred at 1000 cycles. In Comparative Example 4, since the content of Cu was 0.2%, which was out of the range of the present invention, breakage occurred at 1000 cycles.

The most preferred content of Sb is 0.5% by mass. In Example 1 of the present invention, the Sb content in the solder ball was 0.5% by mass, but it is considered that the Sb content in the solder bumps was slightly reduced by the dilution in the solder paste. On the other hand, in Examples 2 and 3 of the present invention, the Sb content in the solder ball was 0.7% by mass,
It is considered that the solder bumps were also diluted and approached a preferable content of 0.5% by mass.
As a result, as shown in Table 2, the heat cycle test 12
In the cycles of 00 to 1600, Examples 2 and 3 of the present invention had better results than Example 1 of the present invention.

Example 2 Evaluation of Impact Resistance Two glass epoxy resin substrates were joined in the same manner as in Example 1 above, using a 300 μm diameter solder ball having the components shown in Table 3. This substrate is screwed on top of an aluminum plate 11 cm wide, 11 cm long and 2 cm thick,
The impact resistance was evaluated by confirming the continuity of each solder joint by dropping from a height of 70 cm. The stage where the resistance changed by 50% or more from the initial connection resistance state was defined as conduction failure and breakage, each set of five substrates was dropped, and the connection reliability was evaluated by the average number of impact resistance.
Inventive Examples 1 to 4 and Comparative Examples 1 to 3 are the same as Example 1. Comparative Example 4 is an example in which the Cu content falls outside the upper limit of the present invention, and Comparative Example 5 is an example in which the Fe content falls outside the upper limit of the present invention.

[0042]

[Table 3]

In each of Examples 1 to 4 of the present invention, the average impact resistance was 8.5 times or more, showing good results. Comparative Examples 2, 3, and 4 all use a conventional anti-fatigue solder alloy, but have an average impact resistance of about 7 times, indicating that the solder alloy of the present invention is excellent in impact resistance. There was found.
In Comparative Example 5, since the Fe content exceeded the upper limit of 0.5% by mass of the present invention, the ductility was significantly reduced, and the average impact resistance reached 3 times in the impact resistance evaluation by dropping. Absent.

[0044]

According to the present invention, Sn-P containing Ag, Sb, Bi, and Cu is used.
By optimizing the range of the Cu content in the b-based solder alloy, a solder alloy having high mechanical strength, excellent fatigue resistance, and excellent impact resistance was obtained. By applying this solder alloy to an electronic member solder bump and an electronic member solder ball, and further to an electronic member having a solder bump, metal fatigue is likely to occur due to repeated stress such as a temperature cycle. With regard to micro solder bonding of electronic components used in the environment, it was possible to prevent fatigue and impact destruction of solder joints.

Continuing on the front page (72) Inventor Kohei Tatsumi 20-1 Shintomi, Futtsu-shi Nippon Steel Corporation Technology Development Division (72) Inventor Hideji Hashino 20-1 Shintomi, Futtsu-shi Technology Development Nippon Steel Corporation Within the headquarters (72) Inventor Shinichi Terashima 20-1 Shintomi, Futtsu City Nippon Steel Corporation Technology Development Headquarters F-term (reference) 5E319 AC01 BB04 BB05 CD26 GG11 GG20

Claims (7)

[Claims] 1. Sn: 55 to 70% by mass, Ag: 0.5
To 5.0% by mass, Sb: 0.1 to 3.0% by mass, Bi:
0.1 to 3.0% by mass, Cu: 0.01 to 0.1% by mass
And the balance consists of Pb and unavoidable impurities, and
A solder alloy having a total content of g, Sb, Bi, and Cu of 5.0% by mass or less. 2. Further, Fe, Ni, Zn, In, Pt,
The solder alloy according to claim 1, wherein one or more metals selected from the group consisting of Pd are contained in a total amount of 0.01 to 0.5% by mass. 3. The solder alloy according to claim 1, further comprising 0.0005 to 0.005% by mass of P. 4. The solder alloy according to claim 1, wherein the solder alloy is used for a solder bump for an electronic member. 5. A solder ball for an electronic member, comprising a solder alloy according to claim 1. Description: 6. An electronic member having solder bumps,
An electronic member, wherein a part or all of the solder bump is formed of the solder alloy according to claim 1. 7. An electronic member in which a plurality of electronic components are joined by a solder electrode, wherein a part or all of the solder electrode is formed by the solder alloy according to claim 1. An electronic member characterized by the above-mentioned.