TWI869730B - Lead-free and copper-free tin alloys and solder balls for ball grid array packaging - Google Patents

Abstract

A lead-free copper-free tin alloy comprises 0.01-3.0 wt% of silver, 0.01-5.0 wt% of bismuth, 0-2.0 wt% of antimony, 0.005-0.1 wt% of nickel, 0.005-0.02 wt% of germanium and the remainder of tin. The structure obtained by welding the lead-free copper-free tin alloy of the present invention, such as a solder bump, has excellent mechanical shock reliability, and also has good weldability, ductility, oxidation resistance and thermal cycling reliability.

Description

Lead-free and copper-free tin alloys and solder balls for ball grid array packaging

The present invention relates to a tin alloy and a tin ball made of the tin alloy for ball grid array packaging, and particularly to a lead-free and copper-free tin alloy and a tin ball made of the lead-free and copper-free tin alloy for ball grid array packaging.

As the number of I/O (input/output) of semiconductor components increases, packaging technology has evolved from wire bonding, which was originally only used for packaging around the chip, to ball grid array (BGA) packaging, which can now be used for packaging on the bottom surface of the chip. The technology is to re-layout the IC pads (I/O distribution) of semiconductor components, distributing the pads on the bottom of the semiconductor components to increase the I/O density.

The conduction methods of ball grid array packaging can be divided into metal bumps, conductive glue and conductive film, among which solder bumps, which belong to metal bump technology, are the most common. Ball grid array packaging can be divided into non-wafer level packaging and wafer level packaging.

Non-wafer-level packaging refers to the process of soldering a silicon chip to an organic substrate by wire bonding or flip chip, then filling the gap between the silicon chip and the organic substrate with underfill, and then soldering a solder ball to the other end of the organic substrate to form a solder bump to form an electronic component. Because the difference in the coefficient of expansion between the organic substrate and the silicon chip is too large, when the temperature of the electronic component itself or the environment changes, the thermal stress caused by the mismatch in coefficient of thermal expansion will cause damage to the solder joints (solder bumps) between the electronic component and the circuit board (the solder joints between the organic substrate and the silicon chip are usually not damaged due to the underfill).

Wafer-level packaging refers to performing most or all of the packaging and testing procedures directly on the silicon wafer before cutting it into individual chips. The chip does not pass through the organic substrate, but the IC pads are re-arranged directly on the chip, and then solder balls are soldered to form solder bumps. Since the size of the packaged chip is almost the same as that of the bare chip, it is called wafer level chip scale package (WLCSP for short). However, due to the large difference in expansion coefficients between silicon chips and circuit boards, the solder joints (solder bumps) that serve as the connector between the two must be able to withstand the thermal stress caused by temperature changes in the electronic components themselves or the environment. In addition, because wafer-level packaging is mostly used in thin and short mobile devices, the solder joints (solder bumps) must also be able to withstand high mechanical shocks.

The main characteristics of existing tin alloys are alloy strength and thermal cycle reliability. However, in the pursuit of improving alloy strength and thermal cycle reliability, the tin alloys often have lower ductility, resulting in poor mechanical shock reliability.

Therefore, how to find a tin alloy that can be used to prepare solder balls for ball grid array (BGA) packaging, and the structure obtained after welding of the tin alloy (such as solder bumps) will have excellent mechanical shock reliability, while having good weldability, ductility, oxidation resistance and thermal cycling reliability, has become the current research target.

Therefore, the first object of the present invention is to provide a lead-free and copper-free tin alloy. The lead-free and copper-free tin alloy can be made into tin balls for ball grid array (BGA) packaging, and the structure obtained by welding the lead-free and copper-free tin alloy (such as solder bump) will have excellent mechanical shock reliability, and at the same time have good weldability, ductility, oxidation resistance and thermal cycling reliability.

Therefore, the lead-free copper-free tin alloy of the present invention, based on the total weight of the lead-free copper-free tin alloy being 100 wt%, comprises: 0.01~3.0 wt% of silver; 0.01~5.0 wt% of bismuth; 0~2.0 wt% of antimony; 0.005~0.1 wt% of nickel; 0.005~0.02 wt% of germanium; and the remainder of tin.

Therefore, the second object of the present invention is to provide a solder ball for ball grid array packaging.

Therefore, the tin ball used for ball grid array packaging of the present invention is made of the aforementioned lead-free and copper-free tin alloy.

The effect of the present invention is that: since the lead-free copper-free tin alloy of the present invention simultaneously contains 0.01-3.0 wt% of silver, 0.01-5.0 wt% of bismuth, 0-2.0 wt% of antimony, 0.005-0.1 wt% of nickel, 0.005-0.02 wt% of germanium and the remainder of tin, the lead-free copper-free tin alloy of the present invention can be made into tin balls for ball grid array (BGA) packaging, and the structure (such as solder bump) obtained by welding the lead-free copper-free tin alloy will have excellent mechanical shock reliability, and at the same time have good weldability, ductility, oxidation resistance and thermal cycling reliability.

The following is a detailed description of the content of the invention:

The lead-free copper-free tin alloy of the present invention comprises 0.01-3.0 wt% of silver, 0.01-5.0 wt% of bismuth, 0-2.0 wt% of antimony, 0.005-0.1 wt% of nickel, 0.005-0.02 wt% of germanium, and the balance of tin, based on the total weight of the lead-free copper-free tin alloy being 100 wt%.

It should be noted that the lead-free and copper-free tin alloy of the present invention does not substantially contain lead (Pb) and does not contain copper (Cu). The aforementioned substantially does not contain lead and does not contain copper means that in principle, as long as lead and copper are not intentionally added to the tin alloy (for example, unintentional but unavoidable impurities or contact during the manufacturing process), therefore, based on the subject matter of the present invention, it can be regarded as substantially free of lead and copper, or can be regarded as lead-free and copper-free. wt% refers to weight percentage, and wt% in this article also refers to weight percentage. In addition, the limitations of the numerical range described in the present invention and the patent scope always include the end value.

In addition, the term "balance of tin" should not be understood to exclude other unintentional but unavoidable impurities in the manufacturing process in order to avoid misunderstanding. Therefore, if it is assumed that impurities exist, "balance of tin" should be understood to make up the weight percentage of the lead-free and copper-free tin alloy to 100 wt% and consist of tin plus unavoidable impurities.

Preferably, the lead-free copper-free tin alloy contains 1.5-2.5 wt % of silver. More preferably, the lead-free copper-free tin alloy contains 1.75-2.25 wt % of silver.

Preferably, the lead-free copper-free tin alloy contains 2-3 wt% bismuth. More preferably, the lead-free copper-free tin alloy contains 2.25-2.75 wt% bismuth.

Preferably, the lead-free copper-free tin alloy contains 0.5-1.5 wt% antimony. More preferably, the lead-free copper-free tin alloy contains 0.75-1.25 wt% antimony.

Preferably, the lead-free copper-free tin alloy contains 0.045-0.055 wt % nickel. More preferably, the lead-free copper-free tin alloy contains 0.0475-0.0525 wt % nickel.

Preferably, the lead-free copper-free tin alloy contains 0.005-0.015 wt % of germanium. More preferably, the lead-free copper-free tin alloy contains 0.0075-0.0125 wt % of germanium.

Preferably, the total weight of bismuth and antimony is 1.0-4.5 wt%. More preferably, the total weight of bismuth and antimony is 3.0-4.0 wt%. More preferably, the total weight of bismuth and antimony is 3.0-3.75 wt%. More preferably, the total weight of bismuth and antimony is 3.25-3.75 wt%.

＜ Embodiment 1~1 1 Comparison example 1~ 9 ＞

Preparation of lead-free, copper-free, tin alloy

The lead-free, copper-free, tin alloys of Examples 1 to 11 and Comparative Examples 1 to 9 are prepared according to the metal composition and weight percentage (wt%) shown in Table 1 below, and the following steps:

Step (1) : Prepare corresponding metal materials according to the corresponding metal components and weight percentages.

Step (2) : The prepared metal material is heated, melted and cast to form the lead-free, copper-free, tin alloys of Examples 1 to 11 and Comparative Examples 1 to 9. Table 1 Lead-free , copper-free, tin alloy Metal content ratio (wt%) Properties test results Sn Ag Bi Sb Ni Ge Thrust test Tensile test Plate-level welding test Hot and cold cycle test Mechanical shock test Overall evaluation results Embodiment 1 Remaining amount 2.0 2.5 1.0 0.05 0.01 ○ ○ ○ ○ ○ ○ Embodiment 2 Remaining amount 0.01 2.5 1.0 0.05 0.01 ○ ○ ○ △ ○ △ Embodiment 3 Remaining amount 3.0 2.5 1.0 0.05 0.01 ○ △ ○ ○ △ △ Embodiment 4 Remaining amount 2.0 0.01 1.0 0.05 0.01 △ ○ ○ △ ○ △ Embodiment 5 Remaining amount 2.0 5.0 1.0 0.05 0.01 ○ △ ○ ○ △ △ Embodiment 6 Remaining amount 2.0 2.5 0 0.05 0.01 ○ ○ ○ △ ○ △ Embodiment 7 Remaining amount 2.0 2.5 2.0 0.05 0.01 △ △ ○ ○ △ △ Embodiment 8 Remaining amount 2.0 2.5 1.0 0.005 0.01 ○ ○ ○ △ ○ △ Embodiment 9 Remaining amount 2.0 2.5 1.0 0.1 0.01 ○ ○ ○ ○ △ △ Embodiment 10 Remaining amount 2.0 2.5 1.0 0.05 0.005 ○ ○ △ ○ ○ △ Embodiment 11 Remaining amount 2.0 2.5 1.0 0.05 0.02 △ ○ ○ ○ ○ △ Comparison Example 1 Remaining amount 0 2.5 1.0 0.05 0.01 ○ ○ ○ X ○ X Comparison Example 2 Remaining amount 4.0 2.5 1.0 0.05 0.01 ○ X ○ ○ X X Comparison Example 3 Remaining amount 2.0 0 1.0 0.05 0.01 △ ○ ○ X ○ X Comparison Example 4 Remaining amount 2.0 6.0 1.0 0.05 0.01 ○ X ○ ○ X X Comparison Example 5 Remaining amount 2.0 2.5 3.0 0.05 0.01 X X ○ ○ X X Comparison Example 6 Remaining amount 2.0 2.5 1.0 0 0.01 ○ ○ ○ X ○ X Comparative Example 7 Remaining amount 2.0 2.5 1.0 0.2 0.01 △ ○ ○ △ X X Comparative Example 8 Remaining amount 2.0 2.5 1.0 0.05 0 ○ ○ X ○ ○ X Comparative Example 9 Remaining amount 2.0 2.5 1.0 0.05 0.05 X ○ △ △ △ X

＜ Alloy property test ＞

First, it is explained that the weldability of the lead-free copper-free tin alloy of the embodiment and the comparative example is evaluated by a thrust test; the ductility of the alloy is evaluated by a tensile test; the oxidation resistance is evaluated by a plate-level welding test; the thermal fatigue resistance of the solder joint and the joint structure (i.e., the thermal cycle reliability) is evaluated by a thermal cycle test; and the mechanical shock resistance of the solder joint and the joint structure (i.e., the mechanical shock reliability) is evaluated by a mechanical shock test.

The test methods for thrust test, plate-level welding test, hot and cold cycle test and mechanical shock test are as follows:

[ Thrust test ]

The solder balls made of lead-free and copper-free tin alloys of the embodiment or comparative example with a ball diameter of 0.45 mm were used to implant the ball grid array (BGA) components (component size was 14 mm×14 mm, and the peak temperature of the implant reflow curve was 240°C). After the implantation, the push force test of the solder bump was performed using a push-pull force tester (the pusher moving speed was 100 μm/s). 15 solder bumps were implanted on each group of alloy BGA samples and their push force strength was recorded. The average push force strength of the 15 solder bumps was taken as the experimental result.

Judgment criteria: If the average thrust strength exceeds 13 Newtons, the ball soldering is judged to be good and marked as "○", if the average thrust strength is between 11 and 13 Newtons, the ball soldering is judged to be acceptable and marked as "△", and if the average thrust strength is less than 11 Newtons, the ball soldering is judged to be insufficient and marked as "X".

[ Tensile test ]

The lead-free, copper-free, tin-free alloys of the embodiments or comparative examples were subjected to tensile tests. The tensile specimen preparation and test method were performed in accordance with the ASTM E8 standard. The tensile rate was 6 mm/min. The elongation results of the tensile test were used to compare the ductility of the alloys. In this test, three tensile specimens were tested for each alloy, and the average of the three elongation results was taken.

Judgment criteria: If the average elongation is greater than 25%, the alloy is judged to have good ductility and marked as "○", if the average elongation is between 20~25%, the alloy is judged to have acceptable ductility and marked as "△", and if the average elongation is less than 20%, the alloy is judged to have insufficient ductility and marked as "X".

[ Plate welding Test ]

The ball grid array (BGA) components were implanted with solder balls made of lead-free copper-free tin alloys of the embodiments or comparative examples with a ball diameter of 0.63 mm (component size was 35 mm×35 mm, and the peak temperature of the implant reflow curve was 250°C). After implantation, the BGA components were placed in high temperature and high humidity (85°C/85% RH) for 240 hours, and then reflowed with the corresponding circuit board samples (the peak temperature of the reflow curve was 245°C). The purpose of this test is to test the oxidation resistance of the solder bumps formed after implantation of the solder balls made of lead-free copper-free tin alloys of the embodiments or comparative examples in the board-level process. The high temperature and high humidity process is used to accelerate the oxidation reaction of the solder bumps on the parts. The oxidation resistance of the alloy will affect the weldability of the solder bumps and the circuit board. If the alloy's oxidation resistance is insufficient, resulting in poor weldability between the solder bumps and the circuit board, the incidence of double ball defects will increase after the board-level process.

This test is to perform X-ray analysis on the double ball occurrence ratio of the sample after the plate is stepped. Judgment standard: if the double ball occurrence ratio is less than 10%, it is judged that the plate step weldability (i.e., anti-oxidation ability) is good and marked as "○", if the double ball occurrence ratio is between 10~20%, it is judged that the plate step weldability (i.e., anti-oxidation ability) is acceptable and marked as "△", and if the double ball occurrence ratio is greater than 20%, it is judged that the plate step weldability (i.e., anti-oxidation ability) fails and is marked as "X".

[ Hot and cold cycle test ]

The ball grid array (BGA) parts were implanted with tin balls made of lead-free and copper-free tin alloys of the embodiment or comparative example with a ball diameter of 0.45 mm (part size was 14 mm×14 mm, and the peak temperature of the implant reflow curve was 250°C). After implantation, the BGA parts were reflowed with the corresponding circuit board samples (the peak temperature of the reflow curve was 245°C), and the samples after welding were subjected to a hot and cold cycle test (the test conditions were -40~125°C, the heating and cooling rates were 15°C/min, the temperature holding time was 10 minutes, and a total of 600 cycles were performed). Then, the samples after the hot and cold cycle were subjected to red ink analysis. The red ink analysis method is to soak the sample in red ink first, remove the part after the ink is dried, and finally perform microscopic observation on the cross section of the solder joint after the part is removed. Each sample is observed for a total of 192 solder joints of the entire part. A BGA part welding sample is made of each lead-free and copper-free tin alloy tin ball in each embodiment or comparative example for red ink test, and each 192 solder joints are observed in cross section. The purpose of this test is to test the thermal fatigue resistance of the lead-free and copper-free tin alloy tin ball solder joints and the solder joint and copper substrate bonding structure of the embodiment or comparative example. If the alloy solder joint itself and the copper substrate bonding structure have insufficient thermal fatigue resistance, the solder joint or bonding structure will be damaged by thermal fatigue under repeated hot and cold cycle stress, thus affecting the reliability of the solder joint. This test performs red ink analysis on the samples after hot and cold cycle. If the solder joint has defects or fractures during the hot and cold cycle test, the cross section of the solder joint will be stained with ink after the red ink test. The degree and amount of ink staining on the cross section of the solder joint represents the degree and amount of damage to the solder joint and bonding structure. Therefore, the thermal fatigue resistance of the solder joint and bonding structure can be judged by comparing the ink staining of different sample solder joints.

Judgment standard: If the ink-stained area of all solder joints does not exceed 50% of the cross-sectional area, the thermal fatigue resistance of the alloy solder joints and the joint structure is judged to be good and marked as "○". If the number of solder joints with ink-stained area exceeding 50% is less than 10, the thermal fatigue resistance of the alloy solder joints and the joint structure is judged to be acceptable and marked as "△". If the number of solder joints with ink-stained area exceeding 50% is more than 10, the thermal fatigue resistance of the alloy solder joints and the joint structure is judged to be poor and marked as "X".

[ Mechanical shock test ]

The ball grid array (BGA) component is implanted with a tin ball made of a lead-free copper-free tin alloy of the embodiment or comparative example with a ball diameter of 0.45 mm (component size is 14 mm×14 mm, and the peak temperature of the implant reflow curve is 250°C). After the implantation, the BGA component is reflowed with the corresponding circuit board sample (the peak temperature of the reflow curve is 245°C), and the sample after the welding is subjected to a mechanical shock test (the test conditions are 1500 g acceleration, 0.5 ms shock dwell time, and a total of 50 shocks). Then, the sample after the mechanical shock test is subjected to red ink analysis. The red ink analysis method is to soak the sample in red ink first, remove the part after the ink is dried, and finally perform microscopic observation on the cross section of the solder joint after the part is removed. Each sample is observed for a total of 192 solder joints of the entire part. The lead-free and copper-free tin alloy tin balls of various embodiments or comparative examples are used to make a welding sample of a BGA part for red ink testing, and each 192 solder joints are observed in cross section. The purpose of this test is to test the mechanical impact resistance of the solder bumps formed after the lead-free and copper-free tin alloy tin balls of the embodiments or comparative examples are implanted, and the bumps and copper substrate bonding structures. If the alloy solder joint itself and the copper substrate bonding structure are not able to resist mechanical shock, the solder joint or bonding structure will not be able to withstand the mechanical shock force and will be damaged, thus affecting the reliability of the solder joint. This test performs red ink analysis on the samples after the mechanical shock test. If the solder joint has defects or fractures during the mechanical shock test, the cross section of the solder joint will be stained with ink after the red ink test. The degree and amount of ink staining on the cross section of the solder joint represents the degree and amount of damage to the solder joint and bonding structure. Therefore, the mechanical shock resistance of the solder joint and bonding structure can be judged by comparing the ink staining of different sample solder joints.

Judgment standard: If the ink-stained area of all solder joints does not exceed 50% of the cross-sectional area, the mechanical impact resistance of the alloy solder joints and the bonding structure is judged to be good and marked as "○". If the number of solder joints with an ink-stained area exceeding 50% is less than 10, the mechanical impact resistance of the alloy solder joints and the bonding structure is judged to be acceptable and marked as "△". If the number of solder joints with an ink-stained area exceeding 50% is more than 10, the mechanical impact resistance of the alloy solder joints and the bonding structure is judged to be poor and marked as "X".

The explanations for Figures 1 to 4 are as follows: the photograph of Figure 1 is a cross-section of a double-ball defective solder joint formed in Comparative Example 1, the photograph of Figure 2 is a cross-section of a normal solder joint formed in Example 1, the photograph of Figure 3 is an observation result that the ink-stained area of the solder joint formed in Comparative Example 1 exceeds 50% of the cross-sectional area, and the photograph of Figure 4 is an observation result that the ink-stained area of the solder joint formed in Example 1 does not exceed 50% of the cross-sectional area.

It is also noted that when the same embodiment or the same comparative example is subjected to the aforementioned four tests of thrust test, plate-level welding test, hot and cold cycle test and mechanical impact test, if any "X" appears in the test results, the "overall evaluation result" column in Table 1 is marked as "X", indicating that this embodiment or comparative example does not meet the requirements of the present invention; if any "△" appears in the test results, the "overall evaluation result" column in Table 1 is marked as "△", indicating that this embodiment or comparative example meets the requirements of the present invention; if "○" appears in all three test results, the "overall evaluation result" column in Table 1 is marked as "○", indicating that this embodiment not only meets the requirements of the present invention but is also the best embodiment.

＜ Alloy property test results and discussion ＞

The following discusses the results obtained based on different silver contents, different bismuth contents, different antimony contents, different nickel contents, different germanium contents, and different copper contents.

[ Different silver content ] Table 2 (extracted from Table 1) Lead-free , copper-free, tin alloy Metal content ratio (wt%) Properties test results Sn Ag Bi Sb Ni Ge Thrust test Tensile test Plate-level welding test Hot and cold cycle test Mechanical shock test Overall evaluation results Embodiment 1 Remaining amount 2.0 2.5 1.0 0.05 0.01 ○ ○ ○ ○ ○ ○ Embodiment 2 Remaining amount 0.01 2.5 1.0 0.05 0.01 ○ ○ ○ △ ○ △ Embodiment 3 Remaining amount 3.0 2.5 1.0 0.05 0.01 ○ △ ○ ○ △ △ Comparison Example 1 Remaining amount 0 2.5 1.0 0.05 0.01 ○ ○ ○ X ○ X Comparison Example 2 Remaining amount 4.0 2.5 1.0 0.05 0.01 ○ X ○ ○ X X

As shown in Table 2, the weight percentage of silver will affect the tensile test results (i.e., alloy ductility), the thermal fatigue resistance (i.e., thermal cycling reliability) and mechanical shock resistance (i.e., mechanical shock reliability) of the alloy solder joints and joint structures. Too low a weight percentage of silver will make the lead-free copper-free tin alloy fail to pass the thermal cycling test. Too high a weight percentage of silver will make the lead-free copper-free tin alloy fail to pass the tensile test and mechanical shock test.

Comparative Example 1 does not contain silver, and its thermal cycling test is marked with "X", indicating that too low a weight percentage of silver (less than 0.01 wt%) will result in poor thermal cycling reliability of the alloy; Comparative Example 2 uses 4.0 wt% of silver, and its tensile test and mechanical shock test are marked with "X", indicating that excessive weight percentage of silver (greater than 3.0 wt%) will result in poor ductility and mechanical shock reliability of the alloy; Example 2 uses 0.01 wt% of silver, Example 1 uses 2.0 wt% of silver, and Example 3 uses 3.0 wt% of silver, and they are all marked with "△" or "○" in the "Overall Evaluation Result" column of Table 2, indicating that the lead-free and copper-free tin alloy contains 0.01~3.0 wt% of silver. wt% of silver can meet the requirements of the present invention.

[ Different bismuth contents ] Table 3 (extracted from Table 1) Lead-free , copper-free, tin alloy Metal content ratio (wt%) Properties test results Sn Ag Bi Sb Ni Ge Thrust test Tensile test Plate-level welding test Hot and cold cycle test Mechanical shock test Overall evaluation results Embodiment 1 Remaining amount 2.0 2.5 1.0 0.05 0.01 ○ ○ ○ ○ ○ ○ Embodiment 4 Remaining amount 2.0 0.01 1.0 0.05 0.01 △ ○ ○ △ ○ △ Embodiment 5 Remaining amount 2.0 5.0 1.0 0.05 0.01 ○ △ ○ ○ △ △ Comparison Example 3 Remaining amount 2.0 0 1.0 0.05 0.01 △ ○ ○ X ○ X Comparison Example 4 Remaining amount 2.0 6.0 1.0 0.05 0.01 ○ X ○ ○ X X

As shown in Table 3, the weight percentage of bismuth will affect the tensile test results of the alloy (i.e., alloy ductility), the thermal fatigue resistance of the alloy solder joints and the bonding structure (i.e., thermal cycling reliability), and the mechanical shock resistance (i.e., mechanical shock reliability). Too low a weight percentage of bismuth will cause the lead-free, copper-free, tin alloy to fail the thermal cycling test. Too high a weight percentage of bismuth will cause the lead-free, copper-free, tin alloy to fail the tensile test and mechanical shock test.

Comparative Example 3 does not contain bismuth, and its thermal cycle test is marked as "X", indicating that too low a weight percentage of bismuth (less than 0.01 wt%) will result in poor thermal cycle reliability of the alloy; Comparative Example 4 uses 6.0 wt% of bismuth, and its tensile test and mechanical impact test are marked as "X", indicating that excessive weight percentage of bismuth (greater than 5.0 wt%) will result in poor ductility and mechanical impact reliability of the alloy; Example 4 uses 0.01 wt% of bismuth, Example 1 uses 2.5 wt% of bismuth, and Example 5 uses 5.0 wt% of bismuth, which are all marked as "△" or "○" in the "Overall Evaluation Result" column of Table 3, indicating that the lead-free, copper-free, and tin-free alloy contains 0.01~5.0 wt% of bismuth. wt% of bismuth can meet the requirements of the present invention.

[ Different antimony contents ] Table 4 (extracted from Table 1) Lead-free , copper-free, tin alloy Metal content ratio (wt%) Properties test results Sn Ag Bi Sb Ni Ge Thrust test Tensile test Plate-level welding test Hot and cold cycle test Mechanical shock test Overall evaluation results Embodiment 1 Remaining amount 2.0 2.5 1.0 0.05 0.01 ○ ○ ○ ○ ○ ○ Embodiment 6 Remaining amount 2.0 2.5 0 0.05 0.01 ○ ○ ○ △ ○ △ Embodiment 7 Remaining amount 2.0 2.5 2.0 0.05 0.01 △ △ ○ ○ △ △ Comparison Example 5 Remaining amount 2.0 2.5 3.0 0.05 0.01 X X ○ ○ X X

As shown in Table 4, the weight percentage of antimony affects the thrust test results (i.e. weldability), tensile test results (i.e. alloy ductility), thermal fatigue resistance of solder joints and joint structures (i.e. thermal cycle reliability) and mechanical shock resistance (i.e. mechanical shock reliability). A lower weight percentage of antimony will make the lead-free copper-free tin alloy perform acceptable in the thermal cycle test. Too high a weight percentage of antimony will make the lead-free copper-free tin alloy fail the thrust test, tensile test and mechanical shock test.

Comparative Example 5 uses 3.0 wt% antimony, and its thrust test, tensile test and mechanical impact test are marked as "X", indicating that excessive weight percentage (greater than 2.0 wt%) of antimony will lead to poor weldability, ductility and mechanical impact reliability of the alloy; Example 6 uses 0 wt% antimony, Example 1 uses 1.0 wt% antimony, and Example 7 uses 2.0 wt% antimony, and they are all marked as "△" or "○" in the "Overall Evaluation Result" column of Table 4, indicating that the lead-free copper-free tin alloy containing 0~2.0 wt% antimony can meet the requirements of the present invention.

[ Different nickel contents ] Table 5 (extracted from Table 1) Lead-free , copper-free, tin alloy Metal content ratio (wt%) Properties test results Sn Ag Bi Sb Ni Ge Thrust test Tensile test Plate-level welding test Hot and cold cycle test Mechanical shock test Overall evaluation results Embodiment 1 Remaining amount 2.0 2.5 1.0 0.05 0.01 ○ ○ ○ ○ ○ ○ Embodiment 8 Remaining amount 2.0 2.5 1.0 0.005 0.01 ○ ○ ○ △ ○ △ Embodiment 9 Remaining amount 2.0 2.5 1.0 0.1 0.01 ○ ○ ○ ○ △ △ Comparative Example 6 Remaining amount 2.0 2.5 1.0 0 0.01 ○ ○ ○ X ○ X Comparison Example 7 Remaining amount 2.0 2.5 1.0 0.2 0.01 △ ○ ○ △ X X

As shown in Table 5, the weight percentage of nickel affects the thermal fatigue resistance (i.e., thermal cycling reliability) and mechanical shock resistance (i.e., mechanical shock reliability) of the alloy solder joint and the joint structure. Too low a weight percentage of nickel will make the lead-free copper-free tin alloy fail to pass the thermal cycling test. Too high a weight percentage of nickel will make the lead-free copper-free tin alloy fail to pass the mechanical shock test.

Comparative Example 6 does not contain nickel, and its thermal cycle test is marked as "X", indicating that too low a nickel percentage (less than 0.005 wt%) will result in poor thermal cycle reliability of the alloy; Comparative Example 7 uses 0.2 wt% nickel, and its mechanical shock test is marked as "X", indicating that excessive nickel percentage (greater than 0.1 wt%) will result in poor mechanical shock reliability of the alloy; Example 8 uses 0.005 wt% nickel, Example 1 uses 0.05 wt% nickel, and Example 9 uses 0.1 wt% nickel, and they are all marked as "△" or "○" in the "Overall Evaluation Result" column of Table 5, indicating that the lead-free and copper-free tin alloy contains 0.005~3.1 wt% nickel can meet the requirements of the present invention.

[ Different Germanium Content ] Table 6 (Excerpt from Table 1) Lead-free , copper-free, tin alloy Metal content ratio (wt%) Properties test results Sn Ag Bi Sb Ni Ge Thrust test Tensile test Plate-level welding test Hot and cold cycle test Mechanical shock test Overall evaluation results Embodiment 1 Remaining amount 2.0 2.5 1.0 0.05 0.01 ○ ○ ○ ○ ○ ○ Embodiment 10 Remaining amount 2.0 2.5 1.0 0.05 0.005 ○ ○ △ ○ ○ △ Embodiment 11 Remaining amount 2.0 2.5 1.0 0.05 0.02 △ ○ ○ ○ ○ △ Comparative Example 8 Remaining amount 2.0 2.5 1.0 0.05 0 ○ ○ X ○ ○ X Comparative Example 9 Remaining amount 2.0 2.5 1.0 0.05 0.05 X ○ △ △ △ X

As shown in Table 6, the weight percentage of germanium affects the thrust test results (i.e., weldability) and plate-level welding test results (i.e., oxidation resistance) of the alloy. Too low a weight percentage of germanium will cause the lead-free copper-free tin alloy to fail the plate-level welding test. Too high a weight percentage of germanium will cause the lead-free copper-free tin alloy to fail the thrust test.

Comparative Example 8 does not contain germanium, and its plate-level welding ring test is marked with "X", indicating that too low a weight percentage (less than 0.005 wt%) of germanium will result in poor oxidation resistance of the alloy; Comparative Example 9 uses 0.05 wt% of germanium, and its thrust test is marked with "X", indicating that excessive weight percentage (greater than 0.02 wt%) of germanium will result in poor weldability of the alloy; Example 10 uses 0.005 wt% of germanium, Example 1 uses 0.01 wt% of germanium, and Example 11 uses 0.02 wt% of germanium, and they are all marked with "△" or "○" in the "Overall Evaluation Result" column of Table 6, indicating that the lead-free copper-free tin alloy containing 0.005~0.02 wt% of germanium can meet the requirements of the present invention.

[ Summary ]

According to the above results and discussions, the "Overall Evaluation Result" column of the lead-free copper-free tin alloys of Examples 1 to 11 is marked as "△" or "○", indicating that they can pass the thrust test, board-level welding test, thermal cycling test and mechanical shock test at the same time. This shows that if the lead-free copper-free tin alloy (Examples 1 to 11) of the present invention is used to make solder balls for ball grid array (BGA) packaging, the structure (such as solder bump) obtained after the lead-free copper-free tin alloy is welded will have excellent mechanical shock reliability, and at the same time have good weldability, ductility, oxidation resistance and thermal cycling reliability.

In summary, the lead-free copper-free tin alloy of the present invention contains 0.01-3.0 wt% of silver, 0.01-5.0 wt% of bismuth, 0-2.0 wt% of antimony, 0.005-0.1 wt% of nickel, 0.005-0.02 wt% of germanium and the remainder of tin. Therefore, the lead-free and copper-free tin alloy of the present invention can be made into tin balls for ball grid array (BGA) packaging, and the structure obtained by welding the lead-free and copper-free tin alloy (such as solder bump) will have excellent mechanical shock reliability, and at the same time have good weldability, ductility, oxidation resistance and thermal cycle reliability, so the purpose of the present invention can be achieved.

However, the above is only an example of the implementation of the present invention, and it should not be used to limit the scope of the implementation of the present invention. All simple equivalent changes and modifications made according to the scope of the patent application of the present invention and the content of the patent specification are still within the scope of the patent of the present invention.

Other features and effects of the present invention will be clearly presented in the embodiments with reference to the drawings, wherein: FIG. 1 is a photograph illustrating a cross section of a double ball defective solder joint formed in Comparative Example 1; FIG. 2 is a photograph illustrating a cross section of a normal solder joint formed in Example 1; FIG. 3 is a photograph illustrating the observation result that the ink-stained area of the solder joint formed in Comparative Example 1 exceeds 50% of the cross-sectional area; and FIG. 4 is a photograph illustrating the observation result that the ink-stained area of the solder joint formed in Example 1 does not exceed 50% of the cross-sectional area.

Claims (5)

A lead-free copper-free tin alloy, based on the total weight of the lead-free copper-free tin alloy being 100wt%, the lead-free copper-free tin alloy is composed of: 1.5-2.5wt% of silver; 0.01-2.5wt% of bismuth; 0-2.0wt% of antimony; 0.005-0.1wt% of nickel; 0.005-0.02wt% of germanium; and the remainder of tin. The lead-free copper-free tin alloy as described in claim 1, wherein the lead-free copper-free tin alloy contains 0.5~1.5wt% antimony. The lead-free copper-free tin alloy as described in claim 1, wherein the lead-free copper-free tin alloy contains 0.045~0.055wt% nickel. The lead-free copper-free tin alloy as described in claim 1, wherein the lead-free copper-free tin alloy contains 0.005~0.015wt% germanium. A tin ball for ball grid array packaging is made of the lead-free and copper-free tin alloy described in claim 1.