Lead bonding method for continuous welding

Abstract

The invention belongs to the technical field of chip packaging, and particularly discloses a wire bonding method for continuous welding, which adopts a continuous welding method and an alloy wire bonding and gold wire ball filling method, avoids adverse effects of a heat affected zone of a wire on welding strength through a continuous welding mode, and improves welding quality. A heat affected zone generated during ball making of a first welding point is avoided in an alloy wire bonding and gold wire ball supplementing mode, the defect that the hardness of an alloy wire ball is large is overcome, the vibration strength of an effective lead part is enhanced, connection between a lead and a lead column is more reliable, transition is smoother, high-reliability connection between a chip assembly and a metal Dewar device is achieved, and the service life of the chip assembly and the metal Dewar device is prolonged. The signal output stability and accuracy of the detector are improved, and the assembly yield of the refrigeration type infrared detector is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of chip packaging, and specifically discloses a continuous welding wire bonding method. Background Art

[0002] Refrigerated infrared detectors have the characteristics of high sensitivity, high precision and fast response speed. They are widely used in air-to-air missiles and various infrared reconnaissance, search and tracking systems. For refrigerated infrared detectors with high assembly precision, the quality of wire bonding is one of the important factors affecting the reliability of its signal output, and has a significant impact on the accuracy of the detector's signal transmission. Ultrasonic bonding is one of the commonly used bonding methods. It does not require the addition of current, flux and solder during welding, has no effect on the physical and chemical properties of the welded parts, and will not form any compounds that affect the welding strength. It is a relatively common bonding method in the assembly of refrigerated infrared detectors. However, unreasonable welding methods and process parameters will affect the quality of bonding, resulting in abnormal detector signal output. Therefore, in actual welding, it is necessary to continuously optimize the welding process according to the lead material and welding object.

[0003] The bonding wire is the medium connecting the focal plane chip and the Dewar device. It needs to have high tensile strength, low hardness and low thermal conductivity to meet the high lead reliability and low heat load requirements required for detector packaging. Gold wire and gold alloy wire are commonly used bonding wires. In the detector structure, the bonding distance between the lead column and the chip is large. The alloy wire of grade X-Au69AgPt has good tensile properties and stable arch wire, which can meet the use requirements and obtain good connection effect. Conventional wire bonding consists of a first bonding point, a second bonding point and a wire. The thermal effect generated when the bonding point is balled will cause a heat-affected zone to form on the alloy wire near the root of the solder joint. The alloy wire in this area has large and brittle grains and reduced mechanical properties. Moreover, the detector will be subject to thermal stress caused by system temperature changes and material thermal mismatch and cyclic stress caused by external vibration under working conditions. Under harsh operating conditions, the wire in this weak area may easily crack or even break. In addition, due to the large distance between the chip component and the lead column, the lead span is relatively long. At this time, the existence of the heat-affected zone has a more obvious effect on the quality of wire bonding. Conventional single-point welding methods cannot avoid the generation of heat-affected zones. It is necessary to improve the existing wire bonding methods to improve the quality of long-span wire bonding. Summary of the invention

[0004] In order to solve the problems in the background technology, the present invention discloses a continuous welding wire bonding method, which avoids the adverse effects of the heat affected zone of the wire on the welding strength through continuous welding, avoids the disadvantage of the high hardness of the alloy wire ball through the "alloy wire bonding + gold wire ball filling" method, increases the wire bonding strength between the lead column and the chip in the detector, and improves the stability of the detector signal output.

[0005] In order to achieve the above-mentioned invention object, the present invention adopts the following technical scheme: A continuous welding wire bonding method comprises the following steps: 1) Welding preparation: confirm whether the welding wire installed on the welding machine meets the requirements, and turn on the power of the ultrasonic ball welding machine for preheating; 2) Test welding process: set welding parameters, conduct alloy wire lead welding test on the test piece, the first welding point is located on the lead column during welding, continue to weld continuously on the lead column after the first welding point is completed, the distance between the position of the continuous welding point and the first welding point is not less than 5 times the wire diameter of the alloy wire, the second welding point is on the transition lead piece, after welding is completed, fill gold balls at the continuous welding points and the broken wires of the transition lead piece, and the fill balls cover the lead, after welding is completed, perform a tensile test on the welding wire to ensure that the lead welding strength meets the requirements, if the lead welding strength does not meet the requirements, adjust the welding parameters to ensure that the lead welding strength meets the requirements, obtain the selected welding parameters corresponding to the lead welding strength requirements, and complete the equipment and welding parameter debugging; 3) Welding process: Under the selected welding parameters obtained in step 2), formal device welding is performed. The device is placed on the welding support and placed under the ball welding machine to perform wire welding. During welding, the first welding point is located on the lead column. After the first welding point is completed, continuous welding is continued on the lead column. The distance between the position of the continuous welding point and the first welding point is not less than 5 times the wire diameter of the alloy wire. The second welding point is on the transition lead sheet. After the wire welding is completed, the design drawing is compared to ensure that the wire welding position is accurate; 4) Filling gold balls: Step 3) After the welding process is completed, check under a microscope that there are no cracks, cuts, scratches or folds near the first welding point and continuous welding point of all pins. Then fill gold balls at the continuous welding point and the transition lead wire. The filler balls cover the lead wires. The filler balls at the first welding point and continuous welding point should press the root of the arcing lead wire towards the chip component and keep the arcing root smooth transition; 5) Performance inspection: Use a multimeter to check whether the connectivity and insulation of each pin are normal. After the inspection is correct, perform a functional test. After passing the test, transfer the device to the cold screen bonding process.

[0006] Furthermore, in the continuous welding wire bonding method, step 2) selecting welding parameters includes: ignition current: 50-70 mA, ignition time 600-1100 ms, and tail wire length 300-500 μm.

[0007] Furthermore, in the continuous welding wire bonding method, step 2) selecting welding parameters includes: welding point power range 100-350, time range 150-300ms, and pressure range 15-70g.

[0008] Furthermore, in the continuous welding wire bonding method, in step 2), if the wire becomes detached or the solder joint does not meet the requirements during the welding process, the entire wire should be removed and re-welded, and a tensile test should be performed on the wire after welding is completed.

[0009] Furthermore, in the continuous welding wire bonding method, during step 1) welding preparation, the ultrasonic ball welding machine is preheated for at least 20 minutes.

[0010] Furthermore, in the continuous welding wire bonding method, in steps 2) and 3), all arcs are pulled out by the equipment, the transition is smooth and no tools are required.

[0011] Compared with the prior art, the present invention has the following beneficial effects: The continuous welding wire bonding method of the present invention uses continuous welding and the method of "alloy wire bonding + gold wire ball filling". The adverse effect of the heat affected zone of the lead on the welding strength is avoided by continuous welding. The heat affected zone generated when the first welding point is balled is avoided by the method of "alloy wire bonding + gold wire ball filling", and the disadvantage of the large hardness of the alloy wire ball is avoided. The vibration strength of the effective lead part is enhanced, and the connection between the lead and the lead column is more reliable and the transition is smoother, thereby realizing high-reliability connection between the chip component and the metal Dewar device, improving the stability and accuracy of the detector signal output, and improving the assembly yield rate of the refrigerated infrared detector. DETAILED DESCRIPTION

[0012] In order to better understand the present invention, the content of the present invention is further clearly set forth in conjunction with the embodiments below, but the protection content of the present invention is not limited to the following embodiments. In the following description, a large number of specific details are provided in order to provide a more thorough understanding of the present invention. However, it is obvious to those skilled in the art that the present invention can be implemented without one or more of these details.

[0013] The continuous welding wire bonding method of the present invention has the following detailed steps: 1) Welding preparation: confirm whether the welding wire installed on the welding machine meets the requirements, turn on the power of the ultrasonic ball welding machine and preheat it for at least 20 minutes; 2) Test welding process: Use Shangjin SW450 to set welding parameters, and conduct alloy wire lead welding test on the test piece. During welding, the first weld point is located on the lead column. After the first weld point is completed, continue to weld continuously on the lead column. The distance between the position of the continuous weld point and the first weld point is not less than 5 times the wire diameter of the alloy wire. The second weld point is on the transition lead piece. After welding is completed, fill gold balls at the continuous welding points and the broken wires of the transition lead piece, and the fill balls cover the lead. If the lead is detached or the weld does not meet the requirements during welding, the entire lead should be removed and re-welded. After welding is completed, perform a tensile test on the weld wire to ensure that the lead welding strength meets the requirements. If the lead welding strength does not meet the requirements, adjust the welding parameters to ensure that the lead welding strength meets the requirements, and obtain the selected welding parameters that meet the lead welding strength requirements: ignition current: 50-70 mA, ignition time 600-1100 ms, tail wire length 300-500 μm, welding point power range 100-350 , time range 150-300ms, pressure range 15-70 g, complete the equipment and welding parameter debugging, specific welding parameters need to be adjusted according to the lead diameter, pad material, and tensile strength that the welding lead needs to meet; 3) Welding process: Under the selected welding parameters obtained in step 2), formal device welding is performed. The device is placed on the welding support and placed under the ball welding machine to perform wire welding. During welding, the first welding point is located on the lead column. After the first welding point is completed, continuous welding is continued on the lead column. The distance between the position of the continuous welding point and the first welding point is not less than 5 times the wire diameter of the alloy wire, avoiding the heat-affected zone at the root of the first welding point as an effective lead. The second welding point is on the transition lead sheet. After the wire welding is completed, the design drawing is compared to ensure the accuracy of the welding position; 4) Filling gold balls: After the welding process of step 3 is completed, check under a microscope that there are no cracks, cuts, scratches and folds near the first welding points and continuous welding points of all pins, and then fill gold balls at the continuous welding points and the broken wires of the transition lead wires. The filler balls cover the leads, reducing the risk of brittle fracture at the root of the leads due to the alloy balls being too hard. The filler balls at the first welding points and continuous welding points should press the root of the arc-starting leads toward the chip component and maintain a smooth transition at the arc-starting root. When the lead span is large, the conventional method is to manually use tweezers to shape the welding wires. The cracks, cuts, scratches and other damages caused by the tweezers touching the welding wires are continuously accumulated during the vibration of the detector and eventually cause fatigue fracture of the leads. The present invention uses a continuous welding method, and all arcs are pulled out by equipment, with a smooth transition and no need to use tools, thereby avoiding the risk of lead damage and improving welding wire reliability; 5) Performance inspection: Use a multimeter to check whether the connectivity and insulation of each pin are normal. After the inspection is correct, perform a functional test. After passing the test, transfer the device to the cold screen bonding process.

[0014] The continuous welding wire bonding method of the present invention avoids the heat affected zone generated when the first welding point is balled by using continuous welding and the method of "alloy wire bonding + gold wire ball filling", enhances the vibration strength of the effective lead part, makes the connection between the lead and the lead column more reliable and the transition smoother, and realizes high-reliability connection between the chip component and the metal Dewar device.

[0015] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Other modifications or equivalent substitutions made to the technical solution of the present invention by ordinary technicians in the field should be included in the scope of the claims of the present invention as long as they do not depart from the spirit and scope of the technical solution of the present invention.

Claims

1. A continuous welding wire bonding method, characterized in that: The steps include: 1) Welding preparation: confirm whether the welding wire installed on the welding machine meets the requirements, and turn on the power of the ultrasonic ball welding machine for preheating; 2) Test welding process: set welding parameters, conduct alloy wire lead welding test on the test piece, the first welding point is located on the lead column during welding, continue to weld continuously on the lead column after the first welding point is completed, the distance between the position of the continuous welding point and the first welding point is not less than 5 times the wire diameter of the alloy wire, the second welding point is on the transition lead piece, after welding is completed, fill gold balls at the continuous welding points and the broken wires of the transition lead piece, and the fill balls cover the lead, after welding is completed, perform a tensile test on the welding wire to ensure that the lead welding strength meets the requirements, if the lead welding strength does not meet the requirements, adjust the welding parameters to ensure that the lead welding strength meets the requirements, obtain the selected welding parameters corresponding to the lead welding strength requirements, and complete the equipment and welding parameter debugging; 3) Welding process: Under the selected welding parameters obtained in step 2), perform formal device welding according to the welding method in step 2), place the device on the welding support and place it under the ball welding machine to perform wire welding. During welding, the first welding point is located on the lead column. After the first welding point is completed, continue to weld continuously on the lead column. The distance between the position of the continuous welding point and the first welding point is not less than 5 times the wire diameter of the alloy wire. The second welding point is on the transition lead sheet. Check the design drawing to ensure the accuracy of the welding line position; 4) Filling gold balls: Step 3) After the welding process is completed, check under a microscope that there are no cracks, cuts, scratches or folds near the first welding point and continuous welding point of all pins. Then fill gold balls at the continuous welding point and the transition lead wire. The filler balls cover the lead wires. The filler balls at the first welding point and continuous welding point should press the root of the arcing lead wire towards the chip component and keep the arcing root smooth transition; 5) Performance inspection: Use a multimeter to check whether the connectivity and insulation of each pin are normal. After the inspection is correct, perform a functional test. After passing the test, transfer the device to the cold screen bonding process.

2. The continuous welding wire bonding method according to claim 1, characterized in that: Step 2) Select welding parameters including: ignition current: 50-70 mA, ignition time 600-1100 ms, tail wire length 300-500 μm.

3. The continuous welding wire bonding method according to claim 1, characterized in that: Step 2) Select welding parameters including: welding point power range 100-350, time range 150-300 ms, pressure range 15-70 g.

4. The continuous welding wire bonding method according to claim 1, characterized in that: Step 2) If the lead becomes detached or the solder joint does not meet the requirements during welding, the entire lead should be removed and re-welded. After welding, the wire should be tensile tested.

5. The continuous welding wire bonding method according to claim 1, characterized in that: In step 1) welding preparation, the ultrasonic ball welding machine should be preheated for at least 20 minutes.

6. The continuous welding wire bonding method according to claim 1, characterized in that: In steps 2) and 3), all arcs are pulled out by the equipment, with smooth transitions and no tools required.