阅读说明：本技术 用于半导体芯片焊接锡膏的方法 (Method for soldering tin paste for semiconductor chip ) 是由 焦峰 资春芳 于 2021-09-27 设计创作，主要内容包括：本发明公开了用于半导体芯片焊接锡膏的方法,包括：确定锡膏参数、判断PCB板的尺寸、绘制锡膏特性曲线、印刷焊膏、第一回流焊、去除助焊剂、涂覆助焊剂、第二回流焊和取出PCB板,完成半导体芯片焊接。本发明所述的用于半导体芯片焊接锡膏的方法,通过采用两次回流焊,第一次回流焊接将印刷电路板上锡膏析出的多余助焊剂除去,避免印刷电路板污染,通过在第二次回流焊前涂覆少量树脂型助焊剂,使高压力氮气流动,精准且缓慢地调节回流焊炉温,可减小印刷电路板上的合金焊接层与半导体芯片的引线脚金属接触时产生的表面张力,保证合金焊接层的润湿性,避免半导体芯片和印刷电路板断裂的现象,提高半导体芯片的焊接质量。(The invention discloses a method for welding solder paste for a semiconductor chip, which comprises the following steps: determining solder paste parameters, judging the size of the PCB, drawing a solder paste characteristic curve, printing solder paste, performing first reflow soldering, removing soldering flux, coating the soldering flux, performing second reflow soldering, and taking out the PCB to complete the soldering of the semiconductor chip. The method for welding the tin paste for the semiconductor chip, disclosed by the invention, has the advantages that two times of reflow soldering are adopted, the redundant soldering flux separated out from the tin paste on the printed circuit board is removed by the first reflow soldering, the pollution of the printed circuit board is avoided, a small amount of resin type soldering flux is coated before the second reflow soldering, high-pressure nitrogen flows, the temperature of a reflow soldering furnace is accurately and slowly adjusted, the surface tension generated when an alloy soldering layer on the printed circuit board is in contact with a pin metal of the semiconductor chip can be reduced, the wettability of the alloy soldering layer is ensured, the phenomenon of fracture of the semiconductor chip and the printed circuit board is avoided, and the soldering quality of the semiconductor chip is improved.)

1. A method for soldering a solder paste for a semiconductor chip, characterized by: the method comprises the following steps:

step one, determining solder paste parameters: the method comprises the following steps: initial temperature and temperature rising slope range of the preheating zone; temperature range and time range of the heat preservation area; the peak temperature range, the liquid phase state duration range, the solder paste melting point and the solder paste solidifying point of the reflow region;

step two, judging the size of the PCB: comprises a large plate, a middle plate and a small plate; when the size of the plate is large, the tin paste parameters are all upper limit values, and when the size of the plate is medium and small, the tin paste parameters are all middle values of the upper and lower limits;

step three, drawing a solder paste characteristic curve: adjusting the reflow oven according to the solder paste characteristic curve to enable the temperature of the PCB production oven to accord with the solder paste characteristic curve;

step four, printing soldering paste: printing high-temperature soldering paste to a soldering position of a preset surface-mounted semiconductor chip on one side of the printed circuit board by adopting a steel mesh contact printing mode;

step five, first reflow soldering: carrying out reflow soldering on the printed circuit board printed with the solder paste to form an alloy soldering layer on the printed circuit board, wherein the surface of the printed circuit board is attached with soldering flux precipitated in the solder paste;

step six, removing the soldering flux: cleaning the printed circuit board, and removing the soldering flux precipitated from the tin paste on the surface of the printed circuit board;

step seven, coating soldering flux: coating soldering flux on the surface of the alloy welding layer on the printed circuit board, and mounting a semiconductor chip on the alloy welding layer coated with the soldering flux, wherein the clearance between the pins of the semiconductor chip and the PCB bonding pad is less than 5 mil;

step eight, second reflow soldering: transporting and placing a semiconductor chip subjected to reflow soldering into a sealable process chamber, sealing the process chamber, transporting nitrogen gas pressurized to a pressure higher than a saturated vapor pressure contained at a melting temperature of a flux attached to the semiconductor chip into the process chamber, flowing the high-pressure nitrogen gas in the process chamber, maintaining the process chamber at a pressure higher than the saturated vapor pressure while heating a workpiece to a reflow soldering temperature to keep the temperature of the semiconductor chip constant, melting the flux attached to the semiconductor chip to perform reflow soldering, and cooling the workpiece to solidify the flux;

step nine, taking out the PCB to complete the welding of the semiconductor chip: and after the semiconductor chip is cooled to below the specified temperature, discharging inert gas in the processing chamber to the outside of the processing chamber, opening the processing chamber, taking out the PCB, and fixing the semiconductor chip to be surface-mounted on the alloy welding layer coated with the soldering flux by using a high-temperature reflow soldering technology.

2. The method for semiconductor die bonding solder paste of claim 1, wherein: the temperature of the first reflow soldering in the fifth step is less than or equal to 70 ℃.

3. The method for semiconductor die bonding solder paste of claim 1, wherein: in the seventh step, the coating area of the soldering flux is 80-85% of the area of the welding layer.

4. The method for semiconductor die bonding solder paste of claim 1, wherein: and the soldering flux used in the seventh step is resin type soldering flux.

5. The method for semiconductor die bonding solder paste of claim 1, wherein: in the step eight, the PCB coated with the soldering flux sequentially passes through a preheating zone, an activation zone and a reflow zone in the reflow soldering furnace, the processing time of the PCB in the preheating zone is not more than 110s, and the duration time of the reflow stage is not more than 10 s.

6. The method for semiconductor die bonding solder paste of claim 5, wherein: when in the preheating zone, the semiconductor chip to be welded enters a first temperature-rising stage, a vibration stage and a second temperature-rising stage in sequence, and the vibration stage adopts ultrasonic waves to vibrate the soldering paste; in the first temperature rise stage, the temperature in the preheating zone is raised to 85-90 ℃ at a speed of less than or equal to 5 ℃/s; in a second ramp-up phase, the temperature in the preheating zone is raised to 140 ℃ at a rate of less than or equal to 3 ℃/s.

7. The method for semiconductor die bonding solder paste of claim 5, wherein: in the activation zone, the semiconductor chip to be welded enters a heat preservation stage and a third temperature rise stage in sequence; during the heat preservation phase, the temperature in the activation zone is increased from a first initial temperature to 180 ℃ at a speed of less than or equal to 5 ℃/s; in a third ramp-up phase, the temperature in the activation zone is ramped up to 200 ℃ at a rate of less than or equal to 3 ℃/s.

8. The method for semiconductor die bonding solder paste of claim 7, wherein: the first initial temperature is the temperature in the preheating zone when the semiconductor chip to be welded is processed in the preheating zone, and the duration of the heat preservation stage is 80-90 s.

9. The method for semiconductor die bonding solder paste of claim 5, wherein: in the reflow region, the semiconductor chip to be welded enters a fourth temperature-raising stage, a reflow stage and a first temperature-reducing stage in sequence; wherein, in the reflux stage, the temperature in the reflux zone is kept within 5 ℃ above and below the peak temperature, and the duration of the reflux stage is not more than 6 s; in the fourth temperature rise stage, the temperature in the reflux zone rises from the second initial temperature to the peak temperature at the speed of 2 ℃/s; in the first temperature reduction stage, the temperature in the reflux zone is reduced by 20-30 ℃, and the duration of the first temperature reduction stage is 10-22 s.

10. The method for semiconductor die bonding solder paste of claim 9, wherein: the second initial temperature is the temperature in the activation zone at the end of the treatment of the semiconductor chips to be soldered in the activation zone.

Technical Field

The invention relates to the technical field of semiconductor chip welding, in particular to a method for welding solder paste for a semiconductor chip.

Background

In the electronics manufacturing industry, a large number of surface mount components (SMAs) are soldered using a reflow process. Reflow soldering is a unique important process of Surface Mount Technology (SMT) and is a commonly used process for connecting components to a circuit board, and quality of the reflow soldering process affects not only normal production but also quality and reliability of final products. Reflow soldering is soldering in which a soldering terminal or pin of a surface mount component is mechanically and electrically connected to a pad of a printed board by re-melting a paste soft solder (solder paste) pre-distributed to the pad of the printed board by using a heating device, thereby realizing a circuit function with certain reliability, and is mainly suitable for soldering the surface mount component and the printed board.

In the process of welding a semiconductor chip and a printed circuit board by the conventional solder paste reflow welding process, if the distance between the circuit board and the edges of two sides of a bottom plate is small, a large amount of soldering flux is easy to overflow to the back surface of the bottom plate, and organic molecules generated by the soldering flux at high temperature can seep into a nickel-plated layer of the bottom plate to cause the surface of the bottom plate to be polluted. Accordingly, we propose a method for soldering a solder paste for a semiconductor chip.

Disclosure of Invention

The main object of the present invention is to provide a method for soldering a solder paste to a semiconductor chip, which can effectively solve the problems of the background art.

In order to achieve the purpose, the invention adopts the technical scheme that:

a method for soldering a solder paste for a semiconductor chip, comprising the steps of:

step one, determining solder paste parameters: the method comprises the following steps: initial temperature and temperature rising slope range of the preheating zone; temperature range and time range of the heat preservation area; the peak temperature range, the liquid phase state duration range, the solder paste melting point and the solder paste solidifying point of the reflow region;

step two, judging the size of the PCB: comprises a large plate, a middle plate and a small plate; when the size of the plate is large, the tin paste parameters are all upper limit values, and when the size of the plate is medium and small, the tin paste parameters are all middle values of the upper and lower limits;

step three, drawing a solder paste characteristic curve: adjusting the reflow oven according to the solder paste characteristic curve to enable the temperature of the PCB production oven to accord with the solder paste characteristic curve;

step four, printing soldering paste: printing high-temperature soldering paste to a soldering position of a preset surface-mounted semiconductor chip on one side of the printed circuit board by adopting a steel mesh contact printing mode;

step five, first reflow soldering: carrying out reflow soldering on the printed circuit board printed with the solder paste to form an alloy soldering layer on the printed circuit board, wherein the surface of the printed circuit board is attached with soldering flux precipitated in the solder paste;

step six, removing the soldering flux: cleaning the printed circuit board, and removing the soldering flux precipitated from the tin paste on the surface of the printed circuit board;

step seven, coating soldering flux: coating soldering flux on the surface of the alloy welding layer on the printed circuit board, and mounting a semiconductor chip on the alloy welding layer coated with the soldering flux, wherein the clearance between the pins of the semiconductor chip and the PCB bonding pad is less than 5 mil;

step eight, second reflow soldering: transporting and placing a semiconductor chip subjected to reflow soldering into a sealable process chamber, sealing the process chamber, transporting nitrogen gas pressurized to a pressure higher than a saturated vapor pressure contained at a melting temperature of a flux attached to the semiconductor chip into the process chamber, flowing the high-pressure nitrogen gas in the process chamber, maintaining the process chamber at a pressure higher than the saturated vapor pressure while heating a workpiece to a reflow soldering temperature to keep the temperature of the semiconductor chip constant, melting the flux attached to the semiconductor chip to perform reflow soldering, and cooling the workpiece to solidify the flux;

step nine, taking out the PCB to complete the welding of the semiconductor chip: and after the semiconductor chip is cooled to below the specified temperature, discharging inert gas in the processing chamber to the outside of the processing chamber, opening the processing chamber, taking out the PCB, and fixing the semiconductor chip to be surface-mounted on the alloy welding layer coated with the soldering flux by using a high-temperature reflow soldering technology.

Preferably, the temperature of the first reflow in the fifth step is less than or equal to 70 ℃.

Preferably, the coating area of the soldering flux in the seventh step is 80-85% of the area of the soldering layer.

Preferably, the flux used in the seventh step is a resin type flux.

Preferably, in the eighth step, the PCB coated with the soldering flux sequentially passes through a preheating zone, an activation zone and a reflow zone in the reflow furnace, the processing time of the PCB in the preheating zone is not more than 110s, and the duration of the reflow stage is not more than 10 s.

Preferably, when in the preheating zone, the semiconductor chip to be welded enters a first temperature-raising stage, a vibration stage and a second temperature-raising stage in sequence, and the vibration stage adopts ultrasonic waves to vibrate the soldering paste; in the first temperature rise stage, the temperature in the preheating zone is raised to 85-90 ℃ at a speed of less than or equal to 5 ℃/s; in a second ramp-up phase, the temperature in the preheating zone is raised to 140 ℃ at a rate of less than or equal to 3 ℃/s.

Preferably, in the activation zone, the semiconductor chip to be welded enters a heat preservation stage and a third temperature rise stage in sequence; during the heat preservation phase, the temperature in the activation zone is increased from a first initial temperature to 180 ℃ at a speed of less than or equal to 5 ℃/s; in a third ramp-up phase, the temperature in the activation zone is ramped up to 200 ℃ at a rate of less than or equal to 3 ℃/s.

Preferably, the first initial temperature is the temperature in the preheating zone at the end of the treatment of the semiconductor chip to be welded in the preheating zone, and the duration of the heat preservation stage is 80-90 s.

Preferably, in the reflow zone, the semiconductor chip to be soldered enters a fourth temperature-raising stage, a reflow stage and a first temperature-lowering stage in sequence; wherein, in the reflux stage, the temperature in the reflux zone is kept within 5 ℃ above and below the peak temperature, and the duration of the reflux stage is not more than 6 s; in the fourth temperature rise stage, the temperature in the reflux zone rises from the second initial temperature to the peak temperature at the speed of 2 ℃/s; in the first temperature reduction stage, the temperature in the reflux zone is reduced by 20-30 ℃, and the duration of the first temperature reduction stage is 10-22 s.

Preferably, the second initial temperature is the temperature in the activation zone at the end of the treatment of the semiconductor chips to be soldered in the activation zone.

Compared with the prior art, the invention has the following beneficial effects:

1. the invention adopts twice reflow soldering to solder the semiconductor chip, and performs reflow soldering on the printed circuit board printed with the solder paste through the first reflow soldering, so as to form an alloy soldering layer on the printed circuit board and remove the redundant soldering flux separated out from the solder paste on the printed circuit board;

2. according to the invention, a small amount of resin type soldering flux is coated on the surface of the alloy welding layer before the second reflow soldering, and because the coating amount of the coating soldering flux is small, the coating can enable the soldering flux to be completely volatilized during the second reflow soldering, organic molecules cannot be generated to pollute the printed circuit board, and the resin type soldering flux can reduce the surface tension generated when the alloy welding layer on the printed circuit board is in metal contact with the lead pins of the semiconductor chip, enhance the surface wetting force and ensure the wettability of the alloy welding layer;

3. according to the invention, by combining various parameters of the solder paste and determining each section of curve according to the size of the printed circuit board to be soldered, the temperature requirement of the reflow soldering furnace is objectively presented, the temperature standard of the reflow soldering furnace is given, the reflow soldering quality is improved, the appropriate reflow soldering furnace temperature can be simply and rapidly found, the possibility of cracking of the printed circuit board in the heating process can be reduced, and the soldering quality of the semiconductor chip is improved;

4. according to the invention, the high-pressure nitrogen flows in the processing chamber, so that the phenomenon of intermittent wetting can be weakened, further the oxidation of a soldering paste film is reduced, the soldering paste and pin bridging of a semiconductor chip are protected, the boiling and splashing of the soldering paste can be effectively limited by controlling the temperature rise to be continuously at a slow speed, small tin balls are prevented from being formed, the phenomenon of breakage of the semiconductor chip and a printed circuit board is avoided, and the welding effect is improved.

Drawings

FIG. 1 is a flow chart of the soldering process for soldering a solder paste for a semiconductor chip according to the present invention.

Detailed Description

In order to make the technical means, the creation characteristics, the achievement purposes and the effects of the invention easy to understand, the invention is further described with the specific embodiments.

In the description of the present invention, it should be noted that the terms "upper", "lower", "inner", "outer", "front", "rear", "both ends", "one end", "the other end", and the like indicate orientations or positional relationships based on those shown in the drawings, and are only for convenience of description and simplicity of description, but do not indicate or imply that the referred device or element must have a specific orientation, be constructed in a specific orientation, and be operated, and thus, should not be construed as limiting the present invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.

In the description of the present invention, it is to be noted that, unless otherwise explicitly specified or limited, the terms "mounted," "disposed," "connected," and the like are to be construed broadly, such as "connected," which may be fixedly connected, detachably connected, or integrally connected; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meanings of the above terms in the present invention can be understood in specific cases to those skilled in the art.

Examples

A method for soldering a solder paste for a semiconductor chip, comprising the steps of:

step one, determining solder paste parameters: the method comprises the following steps: initial temperature and temperature rising slope range of the preheating zone; temperature range and time range of the heat preservation area; the peak temperature range, the liquid phase state duration range, the solder paste melting point and the solder paste solidifying point of the reflow region;

step two, judging the size of the PCB: comprises a large plate, a middle plate and a small plate; when the size of the plate is large, the tin paste parameters are all upper limit values, and when the size of the plate is medium and small, the tin paste parameters are all middle values of the upper and lower limits;

step three, drawing a solder paste characteristic curve: adjusting the reflow oven according to the solder paste characteristic curve to enable the temperature of the PCB production oven to accord with the solder paste characteristic curve;

step four, printing soldering paste: printing high-temperature soldering paste to a soldering position of a preset surface-mounted semiconductor chip on one side of the printed circuit board by adopting a steel mesh contact printing mode;

step five, first reflow soldering: carrying out reflow soldering on the printed circuit board printed with the solder paste to form an alloy soldering layer on the printed circuit board, wherein the surface of the printed circuit board is attached with soldering flux precipitated in the solder paste, and the temperature of the first reflow soldering is less than or equal to 70 ℃;

step six, removing the soldering flux: cleaning the printed circuit board, and removing the soldering flux precipitated from the tin paste on the surface of the printed circuit board;

step seven, coating soldering flux: coating a soldering flux on the surface of an alloy welding layer on the printed circuit board, wherein the soldering flux is a resin type soldering flux, the coating area of the soldering flux is 80% -85% of the area of the welding layer, mounting a semiconductor chip on the alloy welding layer coated with the soldering flux, and the gap between a pin of the semiconductor chip and a PCB pad is less than 5 mil;

step eight, second reflow soldering: transporting and placing a semiconductor chip subjected to reflow soldering into a sealable process chamber, sealing the process chamber, transporting nitrogen gas pressurized to a pressure higher than a saturated vapor pressure contained at a melting temperature of a flux attached to the semiconductor chip into the process chamber, flowing the high-pressure nitrogen gas in the process chamber, maintaining the process chamber at a pressure higher than the saturated vapor pressure while heating a workpiece to a reflow soldering temperature to keep the temperature of the semiconductor chip constant, melting the flux attached to the semiconductor chip to perform reflow soldering, and cooling the workpiece to solidify the flux; the PCB coated with the soldering flux sequentially passes through a preheating zone, an activation zone and a reflow zone in a reflow soldering furnace, the processing time of the PCB in the preheating zone is not more than 110s, the duration time of the reflow stage is not more than 10s, when the PCB is in the preheating zone, a semiconductor chip to be welded sequentially enters a first temperature rise stage, a vibration stage and a second temperature rise stage, and the vibration stage adopts ultrasonic waves to vibrate the soldering paste; in the first temperature rise stage, the temperature in the preheating zone is raised to 85-90 ℃ at a speed of less than or equal to 5 ℃/s; in the second temperature rise stage, the temperature in the preheating zone is increased to 140 ℃ at a speed of less than or equal to 3 ℃/s; in the activation zone, the semiconductor chip to be welded enters a heat preservation stage and a third temperature rise stage in sequence; during the heat preservation phase, the temperature in the activation zone is increased from a first initial temperature to 180 ℃ at a speed of less than or equal to 5 ℃/s; in the third temperature rise stage, the temperature in the activation zone is raised to 200 ℃ at the speed of less than or equal to 3 ℃/s, the first initial temperature is the temperature in the preheating zone when the treatment of the semiconductor chip to be welded in the preheating zone is finished, and the duration of the heat preservation stage is 80-90 s; in the reflow region, the semiconductor chip to be welded enters a fourth temperature-raising stage, a reflow stage and a first temperature-reducing stage in sequence; wherein, in the reflux stage, the temperature in the reflux zone is kept within 5 ℃ above and below the peak temperature, and the duration of the reflux stage is not more than 6 s; in the fourth temperature rise stage, the temperature in the reflux zone rises from the second initial temperature to the peak temperature at the speed of 2 ℃/s; in the first cooling stage, the temperature in the reflux zone is reduced by 20-30 ℃, and the duration of the first cooling stage is 10-22 s; the second initial temperature is the temperature in the activation zone at the end of the treatment of the semiconductor chip to be welded in the activation zone;

step nine, taking out the PCB to complete the welding of the semiconductor chip: and after the semiconductor chip is cooled to below the specified temperature, discharging inert gas in the processing chamber to the outside of the processing chamber, opening the processing chamber, taking out the PCB, and fixing the semiconductor chip to be surface-mounted on the alloy welding layer coated with the soldering flux by using a high-temperature reflow soldering technology.

The invention adopts twice reflow soldering to solder the semiconductor chip, and performs reflow soldering on the printed circuit board printed with the solder paste through the first reflow soldering, so as to form an alloy soldering layer on the printed circuit board and remove the redundant soldering flux separated out from the solder paste on the printed circuit board; the resin type soldering flux can reduce the surface tension generated when the alloy welding layer on the printed circuit board is in contact with the pin metal of the semiconductor chip, enhance the surface wetting force and ensure the wettability of the alloy welding layer; by combining various parameters of the solder paste and determining each section of curve according to the size of the printed circuit board to be soldered, the temperature requirement of the reflow soldering furnace is objectively presented, the temperature standard of the reflow soldering furnace is given, the reflow soldering quality is improved, the proper reflow soldering furnace temperature can be simply and quickly found, the possibility of cracking of the printed circuit board in the heating process can be reduced, and the soldering quality of the semiconductor chip is improved; flowing in the treatment chamber through high pressure nitrogen gas, can weakening intermittent wetting phenomenon, and then reduced the oxidation of soldering paste membrane, protected soldering paste and semiconductor chip's pin bridging, and continuously be in slow speed through the control intensification, can effectively restrict the boiling of solder paste and splash, prevent to form little tin pearl, avoid semiconductor chip and printed circuit board cracked phenomenon, improve welding effect.

The foregoing shows and describes the general principles and broad features of the present invention and advantages thereof. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, which are described in the specification and illustrated only to illustrate the principle of the present invention, but that various changes and modifications may be made therein without departing from the spirit and scope of the present invention, which fall within the scope of the invention as claimed. The scope of the invention is defined by the appended claims and equivalents thereof.