Method for preparing ball grid array (BGA) solder ball by spot-coating solder paste

Abstract

The invention discloses a method for preparing a ball grid array (BGA) solder ball by dispensing solder paste, which comprises the following steps of: preparing the solder paste from tin-based solder powder and flux paste, filling the solder paste into a needle cylinder of a dispenser, and installing a matched needle head according to the particle size of the BGA solder ball to be prepared; calculating the dosage of the solder paste, and setting the air pressure of a dispensing machine, the tin dispensing speed and the tin dispensing mode; starting a dispensing machine, and dispensing the solder paste on the smooth flat plate carrier by the dispensing machine; heating the flat carrier, melting and cooling the soldering tin to form a solder ball; and the solder balls are taken down, roundness sorting is carried out, and finished BGA solder balls are obtained. The preparation method is simple, the particle size of the BGA solder ball can be accurately controlled, the particle size uniformity is good, and the production efficiency is high.

Description

Technical Field

[0001] The invention belongs to the technical field of welding materials, and in particular relates to a method for preparing BGA solder balls by spot-coating solder paste. Background Art

[0002] BGA solder balls are key materials for integrated circuit packaging. The current preparation methods include cutting and spraying. The cutting method is to cut the tin bars (wires) into particles, and then screen them after oil bath-molding-washing to obtain solder balls. The particle size of the solder balls prepared by the cutting method is relatively uniform, but it is only suitable for preparing large-sized BGA solder balls with a diameter of Φ>0.8mm. The efficiency of preparing small-sized BGA solder balls with a diameter of Φ<0.2mm is low, and the oil on the surface of the prepared solder balls is difficult to clean, which can easily lead to welding failure; the spraying method is to melt the solder and spray it into small metal droplets to form in a protective gas medium. The advantage of this method is that it can atomize small BGA solder balls, but the prepared solder balls have poor roundness, a large particle size range, are difficult to classify, have poor surface finish, and are easy to oxidize. Therefore, most of the current high-quality BGA solder balls in China rely on imports. Summary of the invention

[0003] The purpose of the present invention is to solve the deficiencies of the prior art and to provide a method for preparing BGA solder balls by spot-coating solder paste, which has the advantages of simple preparation method, accurate control of BGA solder ball particle size, good particle size uniformity and high production efficiency.

[0004] In order to achieve the above purpose, the present invention adopts the following technical solutions: A method for preparing BGA solder balls by applying solder paste, comprising the following steps: Tin-based solder powder and flux paste are mixed into solder paste, which is loaded into the syringe of the dispensing machine and a matching needle is installed according to the particle size of the BGA solder ball to be prepared; Calculate the amount of solder paste according to the particle size and mass of the BGA solder ball, and set the soldering pressure, soldering rate and soldering method; Turn on the glue dispenser, and the glue dispenser dispenses solder paste onto a smooth flat carrier; the smooth flat carrier is a ceramic plate or a glass fiber plate made of a material that is not wettable by solder; The flat carrier is heated, the solder paste is heated and the flux volatilizes, the solder melts and cools to form solder balls; Remove the solder balls and sort them for roundness to get finished BGA solder balls; The solder paste includes lead solder paste and lead-free solder paste, and the mass ratio of the solder paste to the solder powder is 9-16%:84-91%; The size of the dispensing needle is 12-35G, which is matched according to the particle size of the BGA solder ball; The tinning pressure is 0.1-0.6MPa, and the tinning rate is 10-300 times / minute; The heating temperature is 100-400° C., and the heating temperature is set according to the melting point of the solder alloy, and the set temperature is 20-60° C. higher than the melting point of the solder alloy.

[0005] The present invention has at least the following advantages: 1. The present invention sets the dispensing machine needle model 12-35G, the tin dispensing pressure 0.1-0.6MPa, and the tin dispensing rate 10-300 times / minute to accurately control the volume and quality of the solder paste. The particle size of the formed BGA solder balls is uniform and no grading treatment is required.

[0006] 2. The preparation method of the present invention shortens the process flow and has high production efficiency. It effectively reduces the problem that the oil stains on the surface of the solder balls prepared by the cutting method are difficult to clean and easily lead to welding failure, and the problem that the BGA solder balls prepared by the spraying method have a large diameter range and are difficult to classify, poor surface finish and are easy to oxidize.

[0007] 3. The present invention can flexibly adjust the metal composition of solder paste solder powder to meet the market demand for multi-element alloys such as SnAgCu-X, SnPb-X, SnBi-X, etc. of BGA solder balls.

[0008] 4. When the BGA solder ball is prepared by the present invention, the resin in the flux paste forms an organic film that wraps around the surface of the BGA solder ball to prevent the surface of the solder ball from being oxidized. The composition of the organic protective film can be adjusted by the composition of the flux paste film-forming agent to adapt to solder balls with various metal components. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 This is a diagram of a BGA solder ball prepared in Example 1 of the present invention; Figure 2 This is a diagram of a BGA solder ball prepared in Example 2 of the present invention; Figure 3 This is a picture of the BGA solder ball prepared in Example 3 of the present invention. DETAILED DESCRIPTION

[0010] The content of the present invention is further described below in conjunction with embodiments.

[0011] Example 1 Preparation of SnPb37 alloy Φ1.5 mm BGA solder balls SnPb37 solder powder with a particle size of 15-40um and flux paste are mixed into solder paste at a mass ratio of 88.5%:11.5%, the solder paste is loaded into a 200CC syringe and the gas is exhausted, and a 15G matching needle is installed; Calculate the mass of solder paste, based on the density of SnPb37 alloy is 8.41g / cm 3, the mass of 1.5mm BGA solder ball is calculated to be 11.14mg, and the mass of solder paste is 12.59mg; the dispensing air pressure of the dispensing machine is set to 0.26Mp, ​​the dispensing rate is 3 times / second, the dispensing controller selects the dotting mode, and the dispensing amount is 12.59±5%mg; Turn on the glue dispenser, which dispenses solder paste onto the smooth ceramic plate; The ceramic plate carrier is heated in a reflow oven with a peak heating temperature of 225°C and a heating rate of 2.5°C / second. During the reflow heating process, the flux evaporates completely, and the solder melts and cools to form solder balls. Remove the solder balls and sort them for roundness. Figure 1 Finished BGA solder balls shown.

[0012] Example 2 Preparation of SnBi35Ag1 alloy Φ1.0 mm BGA solder balls Prepare solder paste by mixing SnBi35Ag1 solder powder with a particle size of 15-45um and flux paste at a mass ratio of 87%:13%, put the solder paste into a 200CC syringe, exhaust the gas, and install an 18G matching needle; Calculate the mass of solder paste, based on the SnBi35Ag1 alloy density of 8.2g / cm 3 , the mass of the 1.50mm solder ball is calculated to be 3.22mg, and the mass of the solder paste is 3.7mg; the dispensing pressure of the dispensing machine is set to 0.22Mp, the dispensing rate is 3 times / second, the dispensing controller selects the dotting mode, and the dispensing amount is 3.7±5%mg; Turn on the glue dispenser, and the glue dispenser will apply solder paste to the smooth fiberglass board; The ceramic board carrier is heated in a reflow oven with a peak heating temperature of 210°C and a heating rate of 2.5°C / second. During the reflow heating process, the flux evaporates completely, and the solder melts and cools to form solder balls. The solder balls were removed and sorted for roundness and particle size. Figure 2 Finished BGA solder balls shown.

[0013] Example 3 Preparation of SnAg3.0Cu0.5 alloy Φ0.4mm BGA solder ball Prepare solder paste by mixing SnAg3.0Cu0.5 solder powder with a particle size of 15-45um and flux paste at a mass ratio of 86%:14%, put the solder paste into a 200CC syringe, exhaust the gas, and install a 24G matching needle; Calculate the mass of solder paste. Calculate the mass of solder paste based on the density of SnAg3.0Cu0.5 alloy, which is 7.4g / cm 3, the mass of the 0.4mm solder ball is calculated to be 0.2mg, and the mass of the solder paste is 0.273mg; the dispensing pressure of the dispensing machine is set to 0.2Mp, the dispensing rate is 3 times / second, and the dispensing controller selects the dotting mode to ensure the dispensing amount of 0.273±5%mg; Turn on the glue dispenser, which dispenses solder paste onto the smooth ceramic plate; The ceramic board carrier is heated in a reflow oven with a peak heating temperature of 245°C and a heating rate of 2.5°C / second. During the reflow heating process, the flux evaporates completely, and the solder melts and cools to form solder balls. Remove the solder balls and sort them for roundness. Figure 3 Finished BGA solder balls shown.

[0014] The specific implementation modes of the present invention are described in detail above, but the present invention is not limited to the above implementation modes. Other implementation cases of the present invention can also be prepared according to the claims. The method of the present invention is convenient, has high production efficiency, can be industrialized and customized, has good uniformity of BGA solder balls, high direct yield of finished products, low cost and obvious economic benefits.

Claims

1. A method for preparing BGA solder balls by applying solder paste, characterized in that: The following steps are involved: (1) Mix tin-based solder powder and flux paste into solder paste, load it into the syringe of the dispensing machine, and install a matching needle according to the particle size of the BGA solder ball to be prepared; (2) Calculate the amount of solder paste according to the particle size and mass of the BGA solder ball, and set the tinning pressure, tinning rate and tinning method; (3) Turn on the glue dispenser, and the glue dispenser dispenses solder paste onto a smooth flat carrier; the smooth flat carrier is a ceramic plate or a glass fiber plate made of a material that is not wettable by solder; (4) The flat plate carrier is heated, the solder paste is heated and the flux evaporates, the solder melts and cools to form solder balls; (5) Remove the solder balls and sort them for roundness to obtain finished BGA solder balls; The solder paste includes lead solder paste and lead-free solder paste, and the mass ratio of the solder paste to the solder powder is 9-16%:84-91%; The dispensing needle models include 12-35G, which are matched according to the particle size of the BGA solder ball; The tinning pressure is 0.1-0.6MPa, and the tinning rate is 10-300 times / minute; The heating temperature is 100-400° C., and the heating temperature is set according to the melting point of the solder alloy, and the set temperature is 20-60° C. higher than the melting point of the solder alloy.

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