TWI762119B - Lead-Free Copper-Free Tin Alloys and Solder Balls for Ball Grid Array Packaging - Google Patents

Abstract

A lead-free copper-free tin alloy comprising 3.0-5.0 wt% silver, 0.01-3.5 wt% bismuth, 0.01-3.5 wt% antimony, 0.005-0.1 wt% nickel, 0.005-0.02 wt% germanium and the balance tin. The lead-free copper-free tin alloy of the present invention can be made into tin balls for ball grid array packaging, and the solder bumps formed by the tin balls can withstand the thermal stress brought by the temperature change of the electronic element itself or the environment, as well as the ability to withstand high mechanical shocks at the same time.

Description

Lead-Free Copper-Free Tin Alloys and Solder Balls for Ball Grid Array Packaging

The present invention relates to a tin alloy and tin balls made of the tin alloy for ball grid array packaging, in particular to a lead-free copper-free tin alloy and a tin ball made of the lead-free copper-free tin alloy for Solder balls for ball grid array packages.

With the increase in the number of I/Os (input/output) of semiconductor devices, packaging technology has evolved from wire bonding (wire bonding) that can only be packaged around the chip to ball grid array (BGA) that can be packaged using the bottom surface of the chip. Ball grid array (BGA for short) packaging, the technology of which is to re-layout the IC pads (I/O distribution) of the semiconductor components, and distribute the pads on the bottom of the semiconductor components to increase the I/O density.

The conduction methods of the ball grid array package can be divided into metal bumps, conductive adhesives and conductive films, among which solder bumps, which belong to metal bump technology, are the main ones. Ball grid array packaging can be divided into non-wafer level packaging and wafer level packaging.

Non-wafer-level packaging means that after the silicon chip is soldered to the organic substrate by wire bonding or flip chip, underfill is poured between the silicon chip and the organic substrate, and then the other end of the organic substrate is filled. Solder the solder balls to form solder bumps to form an electronic component. The electronic components will be soldered to the circuit board in a subsequent process to form an assembled circuit board. Because the difference in expansion coefficient between silicon wafer, organic substrate and circuit board is too large, when the temperature of the assembled circuit board itself or the environment changes, the thermal expansion caused by the mismatch in coefficient of thermal expansion Stress can cause damage to the solder joints (solder bumps) between the electronic components and the circuit board, while the solder joints between the organic substrate and the silicon die are usually not damaged due to the underfill.

Wafer-level packaging means that most or all of the packaging and testing procedures are directly performed on the silicon wafer, and then cut into a single chip. The chip does not pass through the organic substrate, but is directly on the chip. layout and then solder balls to form solder bumps. Since the size of the packaged chip is almost the same as that of the bare chip, it is called a wafer level chip scale package (WLCSP for short). However, due to the large difference between the expansion coefficients of the silicon wafer and the circuit board, the solder joints (solder bumps) that serve as the connection between the two must be able to withstand the thermal stress caused by the temperature changes of the electronic components themselves or the environment. In addition, Because wafer-level packaging is mostly used in mobile devices that are thin and short, the solder joints (solder bumps) also need to have the ability to withstand high mechanical shocks.

Therefore, how to find a tin alloy that can be used to make solder balls for ball grid array (BGA) packages, and the solder bumps made from the solder balls can withstand the temperature changes caused by the electronic components themselves or the environment. The thermal stress and the ability to withstand high mechanical shock at the same time have become the target of current research.

Therefore, the first object of the present invention is to provide a lead-free copper-free tin alloy. The lead-free copper-free tin alloy can be made into solder balls for ball grid array (BGA) packaging, and the solder bumps formed by the solder balls can withstand the thermal stress brought by the temperature change of the electronic component itself or the environment , as well as the ability to withstand high mechanical shocks at the same time.

Thus, the lead-free copper-free tin alloy of the present invention, based on the total weight of the lead-free copper-free tin alloy as 100 wt %, comprises: 3.0~5.0 wt% silver; 0.01~3.5 wt% of bismuth; 0.01~3.5 wt% of antimony; 0.005~0.1 wt% nickel; 0.005 to 0.02 wt% germanium; and balance of tin.

Therefore, the second object of the present invention is to provide a solder ball for ball grid array packaging. The solder bumps formed by the solder balls can withstand the thermal stress brought by the temperature change of the electronic component itself or the environment, and at the same time have the ability to withstand high mechanical impact.

Therefore, the solder balls used in the ball grid array package of the present invention are made of the aforementioned lead-free and copper-free tin alloys.

The effect of the present invention is as follows: since the lead-free copper-free tin alloy of the present invention simultaneously contains 3.0-5.0 wt% silver, 0.01-3.5 wt% bismuth, 0.01-3.5 wt% antimony, 0.005-0.1 wt% nickel, 0.005 wt% ~0.02 wt% germanium and balance tin. Therefore, the lead-free copper-free tin alloy of the present invention can be made into solder balls for ball grid array (BGA) packaging, and the solder bumps formed by the solder balls can withstand the temperature changes of the electronic components themselves or the environment. thermal stress, and at the same time have the ability to withstand high mechanical shock.

The content of the present invention will be described in detail below:

The lead-free copper-free tin alloy of the present invention, based on the total weight of the lead-free copper-free tin alloy as 100 wt %, comprises 3.0-5.0 wt % of silver, 0.01-3.5 wt % of bismuth, 0.01-3.5 wt % of antimony, 0.005~0.1 wt% nickel, 0.005~0.02 wt% germanium, and balance tin.

It should be noted that the lead-free copper-free tin alloy of the present invention does not substantially contain lead (Pb) and copper (Cu). The aforementioned not substantially containing lead and copper means that in principle, as long as lead and copper are not intentionally added to the tin alloy, such as unintentional but unavoidable impurities or contact during the manufacturing process, therefore, based on the gist of the present invention, it can be regarded as Essentially free of lead and copper, or considered lead and copper free. wt% refers to the weight percentage, and the following wt% refers to the weight percentage. Additionally, the limits of numerical ranges recited in the present and patent claims are always inclusive of the endpoints.

In addition, the term "residual 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 are present, "the balance of tin" should be understood to make up the weight percent of the lead-free copper-free tin alloy to 100 wt% and consist of tin plus inevitable impurities.

Preferably, the lead-free copper-free tin alloy contains 3.5-4.5 wt% silver. More preferably, the lead-free copper-free tin alloy contains 3.75-4.25 wt% silver.

Preferably, the lead-free copper-free tin alloy contains 2.5-3.5 wt% bismuth. More preferably, the lead-free copper-free tin alloy contains 2.75-3.25 wt% bismuth.

Preferably, the lead-free copper-free tin alloy contains 0.5-1.5 wt % of antimony. More preferably, the lead-free copper-free tin alloy contains 0.75-1.25 wt % of 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% germanium. More preferably, the lead-free copper-free tin alloy contains 0.0075-0.0125 wt% germanium.

< Example 1~11 with the comparative example 1~10 >

Preparation of lead-free copper-free tin alloys

The lead-free and copper-free tin alloys of Examples 1 to 11 and Comparative Examples 1 to 10 are prepared according to the metal composition and weight percent (wt%) shown in Table 1 below, and the following steps:

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

Step (2) : heating, melting and casting the prepared metal material to form the lead-free copper-free tin alloys of Examples 1-11 and Comparative Examples 1-10. Table 1 Metal composition ratio (wt%) Property Test Results Sn Ag Bi Sb Ni Ge thrust hardness stretch Hot and cold cycle Step welding Overall assessment Example 1 margin 4.0 3.0 1.0 0.05 0.01 ○ ○ ○ ○ ○ ○ Example 2 margin 3.0 3.0 1.0 0.05 0.01 ○ △ ○ ○ ○ △ Example 3 margin 5.0 3.0 1.0 0.05 0.01 △ ○ △ △ △ △ Example 4 margin 4.0 0.01 1.0 0.05 0.01 ○ △ ○ △ ○ △ Example 5 margin 4.0 3.5 1.0 0.05 0.01 ○ ○ △ ○ ○ △ Example 6 margin 4.0 3.0 0.01 0.05 0.01 ○ △ ○ △ ○ △ Example 7 margin 4.0 3.0 3.50 0.05 0.01 △ ○ △ ○ △ △ Example 8 margin 4.0 3.0 1.0 0.005 0.01 ○ ○ ○ △ ○ △ Example 9 margin 4.0 3.0 1.0 0.1 0.01 ○ ○ △ ○ ○ △ Example 10 margin 4.0 3.0 1.0 0.05 0.005 ○ ○ ○ ○ △ △ Example 11 margin 4.0 3.0 1.0 0.05 0.02 △ ○ ○ ○ ○ △ Comparative Example 1 margin 2.0 3.0 1.0 0.05 0.01 ○ X ○ X ○ X Comparative Example 2 margin 6.0 3.0 1.0 0.05 0.01 X ○ X X X X Comparative Example 3 margin 4.0 0 1.0 0.05 0.01 ○ X ○ X ○ X Comparative Example 4 margin 4.0 4.0 1.0 0.05 0.01 ○ ○ X △ ○ X Comparative Example 5 margin 4.0 3.0 0 0.05 0.01 ○ X ○ X ○ X Comparative Example 6 margin 4.0 3.0 4.0 0.05 0.01 X ○ X △ X X Comparative Example 7 margin 4.0 3.0 1.0 0 0.01 ○ ○ ○ X ○ X Comparative Example 8 margin 4.0 3.0 1.0 0.2 0.01 ○ ○ X △ ○ X Comparative Example 9 margin 4.0 3.0 1.0 0.05 0 ○ ○ ○ △ X X Comparative Example 10 margin 4.0 3.0 1.0 0.05 0.05 X ○ ○ △ X X "Remainder" is the weight percentage of the lead-free copper-free tin alloy to 100 wt%.

< Alloy property test >

First of all, for the lead-free, copper-free and tin alloys of the examples and comparative examples, the solderability is evaluated by ball shear test; the hardness of the alloy is evaluated by hardness test; Test) to evaluate alloy ductility; to evaluate oxidation resistance by board level soldering test; to evaluate resistance of solder joints and joint structures to thermal fatigue by thermal cycle test.

The test methods for thrust test, hardness test, tensile test, plate step welding test and thermal cycle test are as follows:

[ thrust test ]

Referring to the JESD22-B117B standard test method, the thrust test of the lead-free, copper-free and tin alloys of the Examples and Comparative Examples was carried out. First, apply flux on BGA components with a size of 14 mm × 14 mm, and then use 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 to implant on the BGA components. Ball attach. The surface of the pad of the BGA component is treated as bare copper, and the soldering is performed using a reflow profile with a peak temperature of 240°C. After completion, the solder balls will be soldered to the BGA components to form solder bumps, and then soldered with a thrust tester. The thrust test of the bump (the moving speed of the pusher is 100 μm/s).

Push 15 solder bumps for each combination of gold BGA samples and record their thrust strength. The average thrust strength of the 15 solder bumps is taken as the experimental result. The result judgment standard is: the average thrust strength exceeds 15 Newtons and it is judged as ball-mounting welding If the average thrust strength is between 12 and 15N, it is judged as acceptable and marked as "△". If the average thrust strength is less than 12N, it is judged as insufficient ball mount weldability. and marked with an "X". The thrust test results of the lead-free and copper-free tin alloys of the Examples and Comparative Examples are summarized in Table 1.

[ Hardness Testing ]

According to the ASTM-E92-17 standard test method, the hardness of the lead-free and copper-free tin alloys of the examples and the comparative examples was measured by using a Vickers hardness tester. The test method is to make each alloy into a flat plate-shaped sample with a length of 20 mm, a width of 20 mm and a height of 10 mm. Carry out indentation test (ballast condition: load 500 g, load duration 10 seconds), and then calculate the hardness of the alloy through the size of the indentation left by the alloy sample.

In this test, three hardness samples were tested for each alloy, and then the three hardness results obtained were averaged. The judgment standard was: if the average hardness was greater than 25 Hv, the alloy was judged to have good hardness performance and was marked as "○", and the average hardness When the hardness is between 22 and 25 Hv, it is judged that the hardness of the alloy is acceptable and marked as "△", and the average hardness is less than 22 Hv, the hardness of the alloy is judged to be poor and marked as "X". The hardness test results of the lead-free and copper-free tin alloys of the Examples and Comparative Examples are summarized in Table 1.

[ tensile test ]

With reference to ASTM-E8/E8M-16a, the tensile test of the lead-free and copper-free tin alloys of the Examples and Comparative Examples was carried out. The tensile rate was 6 mm/min, and the elongation of the alloys was compared with the elongation results of the tensile test.

In this test, three tensile samples were tested for each alloy, and then the three elongation results obtained were averaged. The result judgment standard was: if the average elongation was greater than 20%, the alloy was judged to have good ductility and was marked as "○" ”, if the average elongation is between 17% and 20%, it is judged that the alloy has acceptable ductility and is marked as “△”; if the average elongation is less than 17%, it is judged that the alloy has poor ductility and is marked as “X”. The tensile test results of the lead-free and copper-free tin alloys of the Examples and Comparative Examples are summarized in Table 1.

[ Board Step Soldering Test ]

First, apply flux on BGA components with a size of 35 mm × 35 mm, and then use solder balls made of lead-free and copper-free tin alloys of the embodiment or comparative example with a ball diameter of 0.63 mm to implant on the BGA components. Ball attach. The surface of the pad of the BGA component is treated as bare copper, and the soldering is performed using a reflow profile with a peak temperature of 240°C. After completion, the solder balls will be soldered to the BGA component to form solder bumps, and then the sample is placed at a temperature of 85°C. and the relative humidity of 85% for 240 hours to accelerate the oxidation of solder bumps, and then solder the BGA components to the corresponding circuit boards. The surface of the pads of the circuit board is treated with organic solderability preservative (OSP for short). ). The purpose of this test is to test the oxidation resistance of the solder balls made of the lead-free and copper-free tin alloys of the examples or comparative examples after forming solder bumps on BGA components. The oxidation resistance of the alloy will affect the solderability of the solder bumps and the circuit board. If the oxidation resistance of the alloy is insufficient, the solderability of the solder bumps and the circuit board will be poor, which will increase the soldering defects after the board step process. incidence rate.

In this test, X-ray analysis is performed on the samples after the plate step to analyze the proportion of poor welding. The judgment standard is that the proportion of poor welding is less than 10%. The plate is judged to have good weldability and is marked as "○", and the proportion of poor welding is between 10~ 20% is judged to be acceptable in stage weldability and marked as “△”, and if the proportion of poor welding is greater than 20%, it is judged as stage weldability failure and marked as “X”. The board-level soldering test results of the lead-free copper-free tin alloys of the examples and comparative examples are summarized in Table 1.

[ Hot and cold cycle test ]

With reference to JESD22-A104E, the cold-heat cycle test of the lead-free copper-free tin alloys of the examples and comparative examples was carried out. First, apply flux on BGA components with a size of 14 mm × 14 mm, and then use 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 to implant on the BGA components. Ball attach. The surface of the pads of the BGA components is treated as bare copper, and the soldering is performed using a reflow profile with a peak temperature of 240°C. After completion, the solder balls will be soldered to the BGA components to form solder bumps, and then the BGA components will be soldered to the phase. On the corresponding circuit board, the surface of the pad of the circuit board is treated with organic solder protection film (OSP). /min, the holding time is 10 minutes, and a total of 1000 cycles are performed). The resistance (initial resistance value) of each soldered circuit board sample is measured before the cold and heat cycle test, and the resistance is measured again after the cold and heat cycle test (the resistance value after the test). The purpose of this test is to test the thermal fatigue resistance of the solder bumps formed after the lead-free copper-free tin alloy solder balls of the examples or the comparative examples and the joint structure of the solder bumps and the copper substrate. Insufficient thermal fatigue resistance of the copper-substrate bonding structure will lead to thermal fatigue failure of the solder joint or the joint structure under repeated cold-heat cycle stress, thereby affecting the reliability of the solder joint.

In this test, the resistance of the circuit board samples after the cold and heat cycle is tested, and the thermal fatigue resistance of the solder bumps and the bonding structure is judged by comparing the resistance change of the samples after the cold and heat cycle test. The resistance change is defined as the resistance change value (after the test The ratio of the resistance value minus the initial resistance value) to the initial resistance value. Judgment criteria are: if the resistance change is less than 10%, it is judged that the thermal fatigue resistance of the alloy solder joint and the joint structure is good and marked as "○", and the resistance change is 10~20%, it is judged that the alloy solder joint and the joint structure have good thermal fatigue resistance. The thermal fatigue resistance is acceptable and marked as "△", and the resistance change is greater than 20%, it is judged that the thermal fatigue resistance of the alloy solder joint and the joint structure is not good and marked as "X".

1 to 3 are as follows: the photo of FIG. 1 is a slice of a normal solder joint (solder bump) formed in Example 1, and the photo of FIG. 2 is a bad solder joint (solder bump) formed in Comparative Example 9 , the photo in FIG. 3 is the x-ray observation result of the defective solder joints (solder bumps) formed in Comparative Example 9.

In addition, it should be noted that the same embodiment or the same comparative example is subjected to the aforementioned five tests of thrust test, hardness test, tensile test, plate step welding test and cold-heat cycle test. If any "X" appears in the test results, then In Table 1, the column of "Overall Evaluation Result" is marked with "X", which means that this Example or Comparative Example does not meet the requirements of the present invention; The column of "Assessment Results" is marked with "△", which means that this example or the comparative example meets the requirements of the present invention; if "○" appears in all the test results, it is marked in the column of "Overall Assessment Results" in Table 1. "○" means that this embodiment not only meets the requirements of the present invention but also is the best embodiment.

< Alloy property test results and discussion >

In the following, the results obtained with different silver contents, different bismuth contents, different antimony contents, different nickel contents, and different germanium contents are discussed respectively.

[ Different silver content ] Table 2 (extracted from Table 1) Metal composition ratio (wt%) Property Test Results Sn Ag Bi Sb Ni Ge thrust hardness stretch Hot and cold cycle Step welding Overall assessment Example 1 margin 4.0 3.0 1.0 0.05 0.01 ○ ○ ○ ○ ○ ○ Example 2 margin 3.0 3.0 1.0 0.05 0.01 ○ △ ○ ○ ○ △ Example 3 margin 5.0 3.0 1.0 0.05 0.01 △ ○ △ △ △ △ Comparative Example 1 margin 2.0 3.0 1.0 0.05 0.01 ○ X ○ X ○ X Comparative Example 2 margin 6.0 3.0 1.0 0.05 0.01 X ○ X X X X "Remainder" is the weight percentage of the lead-free copper-free tin alloy to 100 wt%.

It can be seen from Table 2 that the weight percentage of silver will affect the hardness of the alloy, the thermal fatigue resistance and oxidation resistance of the solder joints after soldering and the joint interface, and the insufficient oxidation resistance of the solder ball will increase the occurrence of the ball-mounted components in the board-level process. Chances of bad double balls. Too low weight percentage of silver will make the lead-free copper-free tin alloy fail to pass the hardness test and thermal cycle test. Although the weight percentage of silver is too high, it will have higher alloy hardness, but it will lead to the increase of melting point and the decrease of ductility of lead-free and copper-free tin alloy. poor, making it impossible to pass the thrust test, and the reduced ductility of the alloy will also make it impossible to pass the tensile test; in addition, the excessive weight percentage of silver will also cause the lead-free copper-free tin alloy to fail the cold-heat cycle test and board level welding. test.

Comparative Example 1 uses 2.0 wt% silver, which is marked as “X” in the hardness test and cold-heat cycle test, indicating that too low weight percentage (less than 3.0 wt%) of silver will cause alloy hardness performance and alloy solder joints and joint interface heat. The fatigue resistance is not good; Comparative Example 2 uses 6.0 wt% silver, although it is marked as "○" in the hardness test, but in the thrust test, tensile test, cold and heat cycle test, plate step welding test and "overall evaluation results" ” column is marked as “X”, which means that excessive weight percentage (greater than 5.0 wt%) of silver will lead to poor thermal fatigue resistance and insufficient oxidation resistance of solder joints and joint interfaces of the alloy, and cannot pass thrust Test and tensile test; Example 2 uses 3.0 wt% silver, Example 1 uses 4.0 wt% silver, and Example 3 uses 5.0 wt% silver, which are indicated in the "Overall Evaluation Results" column of Table 2 "△" or "○" means that the lead-free copper-free tin alloy containing 3.0-5.0 wt% silver can meet the requirements of the present invention.

[ Different bismuth content ] Table 3 (extracted from Table 1) Metal composition ratio (wt%) Property Test Results Sn Ag Bi Sb Ni Ge thrust hardness stretch Hot and cold cycle Step welding Overall assessment Example 1 margin 4.0 3.0 1.0 0.05 0.01 ○ ○ ○ ○ ○ ○ Example 4 margin 4.0 0.01 1.0 0.05 0.01 ○ △ ○ △ ○ △ Example 5 margin 4.0 3.5 1.0 0.05 0.01 ○ ○ △ ○ ○ △ Comparative Example 3 margin 4.0 0 1.0 0.05 0.01 ○ X ○ X ○ X Comparative Example 4 margin 4.0 4.0 1.0 0.05 0.01 ○ ○ X △ ○ X "Remainder" is the weight percentage of the lead-free copper-free tin alloy to 100 wt%.

It can be seen from Table 3 that the weight percentage of bismuth will affect the hardness of the alloy and the thermal fatigue resistance of the solder joint after welding and the joint interface. Too low weight percentage of bismuth will make the lead-free copper-free tin alloy fail to pass the hardness test and thermal cycle test; too high weight percentage of bismuth will have higher alloy hardness, but will lead to the ductility of lead-free copper-free tin alloy fell and failed the tensile test.

Comparative example 3 uses 0 wt% bismuth, which is marked as "X" in the hardness test and the cold-heat cycle test, indicating that a too low weight percentage (less than 0.01 wt%) of bismuth will cause the alloy hardness performance and alloy solder joints and joint interface heat. The fatigue resistance is not good; Comparative Example 4 uses 4.0wt% bismuth, although it is marked as "○" in the hardness test, but it is marked as "X" in the tensile test and "Overall Evaluation Results" column , the bismuth representing excess weight percentage (greater than 3.5 wt%) will cause the alloy to fail the tensile test; Example 4 adopts 0.01 wt% bismuth, Example 1 adopts 3.0 wt% bismuth, and Example 5 adopts 3.5 wt% bismuth Bismuth, which is marked as "△" or "○" in the column "Overall Evaluation Result" in Table 3, represents that the bismuth containing 0.01 to 3.5 wt% in the lead-free copper-free tin alloy can meet the requirements of the present invention.

[ Different antimony content ] Table 4 (extracted from Table 1) Metal composition ratio (wt%) Property Test Results Sn Ag Bi Sb Ni Ge thrust hardness stretch Hot and cold cycle Step welding Overall assessment Example 1 margin 4.0 3.0 1.0 0.05 0.01 ○ ○ ○ ○ ○ ○ Example 6 margin 4.0 3.0 0.01 0.05 0.01 ○ △ ○ △ ○ △ Example 7 margin 4.0 3.0 3.50 0.05 0.01 △ ○ △ ○ △ △ Comparative Example 5 margin 4.0 3.0 0 0.05 0.01 ○ X ○ X ○ X Comparative Example 6 margin 4.0 3.0 4.0 0.05 0.01 X ○ X △ X X "Remainder" is the weight percentage of the lead-free copper-free tin alloy to 100 wt%.

It can be seen from Table 4 that the weight percentage of antimony will affect the hardness of the alloy, the thermal fatigue resistance and anti-oxidation properties of the solder joints after soldering and the joint interface. Chances of bad double balls. Too low antimony weight percentage will make the lead-free copper-free tin alloy fail to pass the hardness test and the thermal cycle test. Excessive weight percentage of antimony will have higher alloy hardness, but it will lead to the increase of melting point and the decrease of ductility of lead-free and copper-free tin alloy. The poor ductility of the alloy makes it impossible to pass the thrust test, and the ductility of the alloy also makes it impossible to pass the tensile test; in addition, the excessive weight percentage of silver will also cause the lead-free copper-free tin alloy to fail the board step soldering test.

Comparative Example 5 uses 0 wt% of antimony, which is marked as "X" in the hardness test, indicating that too low wt% (less than 0.01 wt%) of antimony will cause the alloy hardness performance to be inconsistent with the thermal fatigue resistance of alloy solder joints and joint interfaces. Good; Comparative Example 6 uses 4.0 wt% antimony, although it is marked as "○" in the hardness test, but it is marked in the thrust test, tensile test, plate welding test and "overall evaluation result" column "X" means that the antimony in excess weight percentage (greater than 3.5 wt%) will lead to insufficient anti-oxidation properties of the alloy, and it cannot pass the thrust test and tensile test; wt% of antimony, Example 7 uses 3.5wt% of antimony, which are marked as "△" or "○" in the "Overall Evaluation Results" column in Table 4, indicating that the lead-free copper-free tin alloy contains 0.01~3.5 wt% of antimony can meet the requirements of the present invention.

[ Different nickel content ] Table 5 (extracted from Table 1) Metal composition ratio (wt%) Property Test Results Sn Ag Bi Sb Ni Ge thrust hardness stretch Hot and cold cycle Step welding Overall assessment Example 1 margin 4.0 3.0 1.0 0.05 0.01 ○ ○ ○ ○ ○ ○ Example 8 margin 4.0 3.0 1.0 0.005 0.01 ○ ○ ○ △ ○ △ Example 9 margin 4.0 3.0 1.0 0.1 0.01 ○ ○ △ ○ ○ △ Comparative Example 7 margin 4.0 3.0 1.0 0 0.01 ○ ○ ○ X ○ X Comparative Example 8 margin 4.0 3.0 1.0 0.2 0.01 ○ ○ X △ ○ X "Remainder" is the weight percentage of the lead-free copper-free tin alloy to 100 wt%.

It can be seen from Table 5 that the weight percentage of nickel will affect the thermal fatigue resistance of the solder joint after welding and the joint interface. Too low nickel weight percentage will make lead-free copper-free tin alloys fail to pass the thermal cycle test; too high nickel weight percentage will have better thermal fatigue resistance of solder joints and joint interfaces, but will lead to lead-free copper-free tin alloys. The ductility of the alloy decreased so that it could not pass the tensile test.

Comparative example 7 uses 0 wt% nickel, which is marked as "X" in the cold-heat cycle test, indicating that too low weight percentage (less than 0.005 wt%) of nickel will lead to poor thermal fatigue resistance of alloy solder joints and joint interfaces; comparison Example 8 uses 0.2 wt% nickel, although it is marked as "○" in the cooling and heating cycle test, but it is marked as "X" in the tensile test and "overall evaluation results" column, which represents the excess weight percentage ( greater than 0.1 wt%) nickel would cause the alloy to fail the tensile test; Example 8 used 0.005 wt% nickel, Example 1 used 0.05 wt% nickel, and Example 9 used 0.1 wt% nickel, as shown in Table 5 The columns of "Overall Evaluation Result" are marked with "△" or "○", which means that the lead-free copper-free tin alloy containing 0.005-0.1 wt% nickel can meet the requirements of the present invention.

[ Different germanium content ] Table 6 (extracted from Table 1) Metal composition ratio (wt%) Property Test Results Sn Ag Bi Sb Ni Ge thrust hardness stretch Hot and cold cycle Step welding Overall assessment Example 1 margin 4.0 3.0 1.0 0.05 0.01 ○ ○ ○ ○ ○ ○ Example 10 margin 4.0 3.0 1.0 0.05 0.005 ○ ○ ○ ○ △ △ Example 11 margin 4.0 3.0 1.0 0.05 0.02 △ ○ ○ ○ ○ △ Comparative Example 9 margin 4.0 3.0 1.0 0.05 0 ○ ○ ○ △ X X Comparative Example 10 margin 4.0 3.0 1.0 0.05 0.05 X ○ ○ △ X X "Remainder" is the weight percentage of the lead-free copper-free tin alloy to 100 wt%.

It can be seen from Table 6 that the weight percentage of germanium will affect the anti-oxidation properties of the alloy, and the insufficient anti-oxidation properties of the solder balls will increase the probability of double-ball defects during the board-level process of the ball-mounted components. Too low weight percent of germanium will make the lead-free copper-free tin alloy fail the board step soldering test; too high weight percent of germanium will cause the solderability of the lead-free copper-free tin alloy to decrease, making it unable to pass the thrust test, and also make the It fails the board level soldering test.

Comparative example 9 uses 0 wt% germanium, which is marked as "X" in the plate-level welding test, indicating that too low weight percentage (less than 0.005 wt%) of germanium will lead to insufficient anti-oxidation properties of the alloy; comparative example 10 uses 0.05 wt% , which is marked as "X" in the thrust test, plate level welding test and the "Overall Evaluation Result" column, indicating that excess weight percent (greater than 0.02 wt%) of germanium will lead to insufficient oxidation resistance of the alloy , and could not pass the thrust test; Example 10 uses 0.005 wt% germanium, Example 1 uses 0.01 wt% germanium, and Example 11 uses 0.02 wt% germanium, which are listed in the "Overall Evaluation Results" column in Table 6 All are marked with "△" or "○", which means that 0.005-0.02 wt% germanium contained in the lead-free copper-free tin alloy can meet the requirements of the present invention.

[ Summarize ]

According to the above results and discussions, the "Overall Evaluation Results" column of the lead-free and copper-free tin alloys of Examples 1 to 11 are all marked with "△" or "○", indicating that they can pass the thrust test, hardness test, Tensile test, board level soldering test and cold-heat cycle test show that if the lead-free copper-free tin alloy (Examples 1-11) of the present invention is used to make solder balls for ball grid array (BGA) packaging, the solder balls will The formed solder bumps can withstand the thermal stress caused by the temperature changes of the electronic components themselves or the environment, and at the same time have the ability to withstand high mechanical shocks.

To sum up, since the lead-free and copper-free tin alloy of the present invention simultaneously contains 3.0-5.0 wt% of silver, 0.01-3.5 wt% of bismuth, 0.01-3.5 wt% of antimony, 0.005-0.1 wt% of nickel, 0.005- 0.02 wt% germanium and balance tin. Therefore, the lead-free copper-free tin alloy of the present invention can be made into solder balls for ball grid array (BGA) packaging, and the solder bumps formed by the solder balls can withstand the temperature changes of the electronic components themselves or the environment. Therefore, it can indeed achieve the purpose of the present invention.

However, the above are only examples of the present invention, and should not limit the scope of the present invention. Any simple equivalent changes and modifications made according to the scope of the application for patent of the present invention and the content of the patent specification are still within the scope of the present invention. within the scope of the invention patent.

Other features and effects of the present invention will be clearly presented in the embodiments with reference to the drawings, wherein: 1 is a photograph illustrating a slice of a normal solder joint (solder bump) formed in Example 1; FIG. 2 is a photograph illustrating a section of a defective solder joint (solder bump) formed in Comparative Example 9; and FIG. 3 is a photograph illustrating the results of x-ray observation of defective solder joints (solder bumps) formed in Comparative Example 9. FIG.

Claims (5)

A lead-free copper-free tin alloy, based on the total weight of the lead-free copper-free tin alloy as 100wt%, comprising: 3.0-5.0wt% silver; 0.01-3.5wt% bismuth; 0.01-3.5wt% antimony; 0.1wt% nickel; 0.005~0.015wt% germanium; and the balance tin. The lead-free copper-free tin alloy according to claim 1, wherein the lead-free copper-free tin alloy contains 2.5-3.5wt% of bismuth. The lead-free copper-free tin alloy according to claim 1, wherein the lead-free copper-free tin alloy contains 0.5-1.5wt% of antimony. The lead-free copper-free tin alloy according to claim 1, wherein the lead-free copper-free tin alloy contains 0.045-0.055wt% nickel. A solder ball for ball grid array packaging is made of the lead-free copper-free tin alloy described in claim 1.

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