CN109411378B

CN109411378B - Preparation method of copper strip winding type welding column

Info

Publication number: CN109411378B
Application number: CN201811366847.6A
Authority: CN
Inventors: 谷岩; 彭程; 王涛; 周天国; 闫琼; 向秀银; 杨慧
Original assignee: Yangtze Normal University
Current assignee: Yangtze Normal University
Priority date: 2018-11-16
Filing date: 2018-11-16
Publication date: 2020-03-17
Anticipated expiration: 2038-11-16
Also published as: CN109411378A

Abstract

The invention discloses a preparation method of a copper strip winding type welding column, which comprises the following steps: s1, preparing a welding core prefabricated body; s2, preparing a welding column prefabricated body; and S3, welding the welding columns. The invention can effectively improve the process defects of high porosity of the welding column, liquefied failure of the welding core and the like caused by reflow soldering, realize high-quality fusion welding of the copper strip and the Pb-Sn welding core, reduce the rejection rate of the copper strip winding type welding column, reduce the power consumption cost of the fusion welding, effectively shorten the preparation time of the welding column, and reduce the manufacturing cost while realizing the preparation of the high-quality copper strip winding type welding column.

Description

Preparation method of copper strip winding type welding column

Technical Field

The invention relates to the field of electronic component packaging, in particular to a method for manufacturing a copper strip winding type welding column.

Background

With the rapid development of electronic information technology, the integration level and complexity of semiconductor devices are higher and higher, and accordingly, the number of pins, the pin density, the operating frequency, and the power consumption involved in the electronic packaging process are continuously increased, so that the conventional packaging technology faces new challenges. The trend is particularly remarkable in logic and microprocessing of service under special working conditions such as military affairs and aerospace. The traditional packaging method can not meet the reliability requirement of electronic device connection in the aspects of electrical property, thermal property, mechanical property and the like.

In order to solve the above problems, IBM and RAYCHEM in the united states respectively and successfully develop a "cast type solder post" made of 90Pb10Sn material and a "copper strip wound type solder post" made of 80Pb20Sn material, which are applied to a novel Ceramic Column Grid Array (CCGA) packaging technology to realize high-reliability connection between a multilayer Ceramic material and a circuit board. The copper strip winding type welding column is widely applied due to the excellent thermal shock resistance and high reliability.

In recent years, China makes great progress in a plurality of high-precision fields including military science and technology, aerospace technology and the like, and the utilization rate of the CCGA technology is also rapidly improved. However, it should be noted that researchers in the domestic CCGA industry have focused more on the fields of development of CCGA array structures, solder column reinforcement, grinding, automatic column planting and other auxiliary CCGA packaging processes, and the core technology of CCGA solder column preparation has been monopolized by the developed countries for a long time. At present, all CCGA welding columns for military use in China are imported from the United states. Research finds that the core technical problem of preparing the qualified copper strip winding type welding column is as follows: because pores are formed between the welding column core part (Pb-Sn alloy for short) and the copper strip wound on the outer side of the welding core, the existence of the pores can improve the stripping tendency of the copper strip and the welding core under the conditions of high power consumption service and thermal shock, and once the copper strip and the welding core are stripped, the reliability of the welding column can be greatly reduced, and even the failure of the whole electronic device is caused. Therefore, the technical key to prolonging the service life of the package and improving the reliability of the welding spot is to reduce the porosity generated in the preparation process of the welding column. The CCGA-related standards set by the united states aeronautics and astronautics authority (NASA) specify that the porosity between the copper strip and the core wire must be strictly controlled to be below 5%. The standard is also accepted by CCGA industries of various countries in the world and becomes a passing standard for judging whether the copper strip winding type welding column is qualified or not.

For the homogeneous connection of pure Sn related to the copper strip winding type welding column, namely the Sn plating layer on the outer surface of the welding core and the Sn plating layer on the inner surface of the copper strip), the currently widely adopted method is single heat source heating, namely reflow soldering. Namely, the temperature is raised under the controlled atmosphere, so that Sn is softened or even melted, and Sn-Sn interface interaction occurs, thereby forming the connection technology. Although the reflow soldering process is excellent in the aspects of atmosphere, temperature control and the like, a plurality of difficulties exist in the preparation process of the CCGA solder column. On one hand, if the temperature is low during fusion welding, the wettability of the Sn-Sn interface and the flowability of the viscous metal are poor, and the gas phase adsorption of the interface is easily wrapped by the Sn melt and is difficult to remove, so that pores are formed at the interface joint after cooling, and the porosity is too high; on the other hand, if the temperature is high during fusion welding, the Pb-Sn alloy of the core wire can deform and even flow out, and the welding column can be directly scrapped. Since the melting point of the Pb-Sn alloy in the core (usually lower than 210 ℃) is always lower than the melting point (232 ℃) of Sn in the plating layer, the occurrence of process defects due to the overall hot working is almost unavoidable.

Disclosure of Invention

Aiming at the defects in the prior art, the invention aims to solve the problems of overhigh porosity caused by the adoption of a reflow soldering process of the existing copper strip winding type welding column and high rejection rate of the welding column caused by deformation and even outflow of a welding core in the welding process due to the fact that the melting point of the welding core is lower than that of a plating layer, and provides the preparation method of the copper strip winding type welding column.

In order to solve the technical problems, the invention adopts the following technical scheme:

the preparation method of the copper strip winding type welding column is characterized by comprising the following steps:

s1 pretreatment of core wire

S11, carrying out Cu electroplating treatment on the Pb-Sn alloy welding core to ensure that the surface of the welding core is uniformly plated with a Cu layer;

s12, further carrying out Sn electroplating treatment on the welding core plated with the Cu layer, and plating a uniform Sn layer outside the Cu layer;

s13, immersing the processed core wire into neutral soldering flux, and fully attaching the soldering flux to the outer surface of the core wire prepared in the step S12 to obtain a core wire preform;

preparation of S2 weld column preform

S21, selecting a copper strip with proper width, and carrying out single-side Sn electroplating treatment on the copper strip;

s22, contacting the Sn-plated surface of the copper strip with the outer surface of the welding core preform prepared in the S13, and uniformly winding the copper strip on the outer surface of the welding core preform by using an electric wire winding machine to prepare a welding column preform;

welding treatment of S3 welding column

S31, putting the weld column preform prepared in the step S22 in a resistance heating furnace coupled by a current field, wherein the specific device mode is as follows: firstly, clamping two ends of a welding column in a direct current circuit, connecting one end of an electrode with a welding core, connecting the other end of the electrode with a copper strip, and then placing the part for clamping the welding column preform in a resistance heating furnace; secondly, regulating the temperature of the electric furnace to 170-195 ℃, then regulating current field parameters, and regulating the current intensity and the voltage intensity in a loop by using a double-temperature double-control direct-current power supply to ensure that the part of the copper strip, which is in solid-solid contact with the welding core, obtains an additional local joule heat source; the fusion welding process is controlled by combining an electric furnace and a current field to prepare a copper strip winding type welding column;

and S32, cutting the copper strip winding type welding column into a standard size.

Further, the core wire preform in the step S1 has a diameter of 0.3 to 0.4 mm.

Further, in the step S2, the width of the copper tape is 0.3 ± 0.1mm, and the distance between the wound copper tapes is 0.23 ± 0.05 mm.

Further, in the step S3, the heating temperature of the resistance heating furnace is 5-20 ℃ lower than the melting point of the Pb-Sn alloy core wire.

Further, in step S3, the current intensity in the dc power supply regulation loop is 0.5A.

Further, in step S3, the energization time in the dc power supply regulation circuit is 5 ± 3 min.

The mechanism of the invention capable of reducing the porosity of the CCGA welding column is as follows: aiming at the problems of low adhesion work and poor wettability caused by oxidation of a welding core and an Sn-Sn interface in the middle stage (heat preservation stage) of reflow soldering process and solidified pores caused by poor metal fluidity in the later stage (cooling stage) of reflow soldering, the low-temperature integral heating and direct-current electric field local heating process provided by the invention can be effectively used for solving the problems. Firstly, in the heat preservation stage of fusion welding, the Sn-Sn interface is affected by oxidation and has poor wettability; the low adhesion causes the generation of interfacial gaps, which form pores after cooling to room temperature, and the application of direct current is effective in breaking the oxide film on the metal surface, thereby reducing the generation of interfacial gaps. Secondly, in the cooling stage of fusion welding, the fluidity of the metal close to the molten state is poor, and when the interface material is cooled and shrunk, the surrounding metal is difficult to 'feed', and the generation of pores is also caused. When direct current is applied to the welding column preform, the integral temperature is below the Sn melting point of the interface, and the solid-phase contact resistance formed by the copper strip and the welding core is very large, so that the Joule heat at the contact interface can be obviously improved in a short time as long as sufficient voltage and current are applied. The increase of the temperature of the contact interface can enhance the metal fluidity of the part and obtain the capacity of full 'feeding', and the tendency of workpiece scrapping caused by the melting and flowing of the Pb-Sn alloy at the core part is greatly weakened because the heat effect only occurs at the micro part of the welding column. Thirdly, after the 'feeding' is finished and the interface forms high-quality fusion welding, the effect of 'poor solid-phase contact, which causes high interface resistivity' automatically disappears, the direct current does not play a role in local heating any more, and the overall temperature of the welding column returns to be below the melting point of the alloy again, so that the overheating failure in the fusion welding process is further avoided.

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

1. the invention can effectively improve the process defects of high porosity of the welding column, liquefied failure of the welding core and the like caused by reflow soldering, realizes high-quality fusion welding of the copper strip and the Pb-Sn welding core, and reduces the rejection rate of the copper strip winding type welding column. As the welding core and the copper strip are heated integrally by the resistance heating furnace and locally by the current field, the welding column preform is heated integrally by the resistance heating furnace, the heating temperature is controlled to be lower than the melting point of the Pb-Sn alloy, and then the two ends of the welding column are clamped in a direct current circuit; therefore, the process defects of high welding column porosity, liquefaction failure of the welding core and the like caused by heating (reflow soldering) by adopting a single heat source are effectively avoided, high-quality fusion welding of the copper strip and the Pb-Sn welding core is realized, and the stability of the integral solid phase of the welding column tissue is maintained.

2. The invention solves the contradiction that the temperature required by fusion welding is higher than the melting point of the core wire, converts the temperature into heat preservation at the temperature lower than the melting point of the core wire, and then applies current field parameter control. Because the phenomenon of high contact interface resistivity disappears along with the completion of fusion welding, the current-assisted fusion welding avoids the influence of fusion welding time on fusion welding quality, simplifies the process, increases the adjustability of the process, and simultaneously improves the fault-tolerant rate of parameter adjustment.

3. The method adopts a current field local heating mode, reduces the power consumption cost of fusion welding, effectively shortens the preparation time of the welding column, and reduces the manufacturing cost while realizing the preparation of the high-quality copper strip winding type welding column.

Drawings

FIG. 1 is a schematic diagram of a current field local heating process and principle of a copper strip wound type welding column of the present invention: (a) a current field local heating process diagram; (b) an interface current line distribution schematic diagram in the fusion welding process; (c) and (4) a current line distribution diagram after fusion welding is completed (interface is completely fused).

FIG. 2 is a microstructure photograph of a Cu tape wound Pb-Sn820 solder column prepared under different process conditions: (d) single heat source (reflow): heating to 225 deg.C, and keeping the temperature for 20 min; (f) the composite heating of the whole heating of the resistance heating furnace and the local heating of the current field: the temperature of the resistance heating furnace is 185 ℃, the current intensity is 0.5A, the voltage is 0.35V, and the temperature is kept for 4 min.

Detailed Description

The invention will be further explained with reference to the drawings and the embodiments.

Example (b):

referring to fig. 1, a Pb-Sn alloy is used as a core wire, and a pure copper thin strip is wound on the core wire to manufacture a copper strip wound type stud.

Firstly, pretreatment of the core wires: taking a Pb-Sn-820 alloy as a core wire, wherein the ratio of Pb: 80 wt%; sn: 20 wt%. Carrying out electroplating Cu treatment on the surface of the welding core to uniformly plate a Cu layer on the surface of the welding core; and further electroplating Sn on the obtained Cu-plated welding core, and plating a uniform Sn layer outside the Cu layer of the welding core. The diameter of the whole welding core after being electroplated is 0.51 +/-0.05 mm. And (4) immersing the electroplated welding core into neutral soldering flux, and fully attaching the soldering flux to the outer surface of the welding core prepared in the step S12 to obtain the welding core preform.

Then, preparing a welding column preform: taking a pure copper thin strip with the width of 0.3mm as a wound copper strip, and carrying out single-side electroplating Sn treatment on the copper strip to uniformly plate an Sn layer on one side of the copper strip; and contacting one side of the copper strip plated with the Sn layer with the outer surface of the welding core preform, so that the Sn layer of the copper strip is contacted with the Sn layer of the welding core preform. And uniformly winding the copper strips on the outer surface of the welding core preform by using an electric wire winding machine, wherein the distance between the wound copper strips is 0.23mm, and thus obtaining the welding column preform.

And finally, welding the welding column prefabricated body: and (3) arranging the welding column preform in a resistance heating furnace coupled by a current field. Specifically, the two ends of the solder post are first clamped in a dc circuit, one end of the electrode is connected to the core wire at one end of the solder post, and the other end of the electrode is connected to the copper strip at the other end of the solder post, as shown in fig. 1 (a). And then placing the welding column prefabricated body into a resistance heating furnace for heat preservation, wherein the temperature of the resistance heating furnace is 185 ℃, and is slightly lower than the melting point of the welding core. At the moment, the Sn-Sn solid phase poor contact interface resistivity of the copper strip and the welding core is very high. And adjusting the bistable double-control direct-current power supply to a current stabilization mode, setting the current intensity to be 0.5A, then opening a current switch-on switch, and recording the stabilized voltage intensity to be about 0.35V. At the initial stage of energization, the current locally forms an aggregation effect at the Sn — Sn interface, and generates a large amount of joule heat, as shown in fig. 1 (b). The localized temperature increase provides additional driving force for the interface metal to flow and repel voids, promoting a higher quality fusion weld at the interface. In addition, after the interface is welded, since the interface is no longer in poor contact, the resistivity drops back to a normal level, and the current crowding effect disappears, as shown in fig. 1 (c), thereby preventing the generation of overheating. And (4) after electrifying for 4min, closing the direct-current power supply and the resistance furnace, and cooling to obtain the copper strip winding type welding column which is subjected to fusion welding. And (4) carrying out tin dipping on the obtained copper strip winding type welding column and cutting the welding column into a standard size to obtain the finished product copper strip winding type welding column.

The microstructure of the copper strip wound type welding column obtained by heating a single heat source (namely, a reflow soldering process without applying an auxiliary heating direct current electric field) and the microstructure of the copper strip wound type welding column obtained in the embodiment of the invention are characterized, wherein the heating temperature of the single heat source heating mode is 225 ℃, and the heat preservation time is 20 min; the embodiment of the invention adopts composite heating: the temperature of the resistance heating furnace is 185 ℃, the current intensity is 0.5A, the voltage is 0.35V, and the heat preservation time is 4 min.

The microstructure of the copper strip wound weld column produced by the two processes is shown in fig. 2. As can be seen from fig. 2 (d), when the winding type solder post is prepared by the reflow soldering process, the bonding portion of the copper tape and the core wire has more pores. Statistical analysis of the porosity was performed on 20 random cross-sectional images using ImageJ software and found to be between 8% and 16%. As can be seen from fig. 2 (f), the copper strip-wound type solder column prepared by the composite heating method of the embodiment of the present invention has few voids between the copper strip and the core wire, and the porosity obtained by statistical analysis of 50 random solder column cross sections with the software is 1.2-3.4%, which meets the industrial standard of CCGA solder columns.

In addition, the fusion welding temperature is low (185 ℃), the fusion welding time is shorter (4 min), high-quality fusion welding of the copper strip and the Pb-Sn welding core is realized, the stability of the integral solid phase of the welding column tissue is kept, the production power consumption is greatly reduced, the preparation time is shortened, the production cost is reduced, and the production efficiency is effectively improved.

Finally, it should be noted that the above embodiments are only used for illustrating the technical solutions of the present invention and not for limiting the technical solutions, and those skilled in the art should understand that modifications or equivalent substitutions can be made on the technical solutions of the present invention without departing from the spirit and scope of the technical solutions, and all that should be covered by the claims of the present invention.

Claims

1. The preparation method of the copper strip winding type welding column is characterized by comprising the following steps:

s1 pretreatment of core wire

preparation of S2 weld column preform

welding treatment of S3 welding column

2. The method for manufacturing a copper tape-wound type stud solder according to claim 1, wherein the core wire preform in step S1 has a diameter of 0.3 to 0.4 mm.

3. The method for manufacturing the copper strip wound type solder post as claimed in claim 1, wherein in step S2, the width of the copper strip is 0.3 ± 0.1mm, and the distance between the wound copper strips is 0.23 ± 0.05 mm.

4. The method for preparing the copper strip wound solder post as claimed in claim 1, wherein in step S3, the heating temperature of the resistance heating furnace is 5-20 ℃ lower than the melting point of the Pb-Sn alloy core wire.

5. The method for manufacturing a copper strip-wound solder post according to claim 1, wherein in step S3, the current intensity in the dc power supply regulating loop is 0.5A.

6. The method for manufacturing a copper strip wound welding column as claimed in claim 5, wherein in step S3, the energizing time in the DC power supply regulating loop is 5 ± 3 min.