JP2016203194A - Manufacturing method of solder bonded body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method which is suitable for preventing solder scattering occurring in solder-bonding, and suppressing generation of voids in solder in manufacturing a solder bonded body in which a first member and a second member are solder-bonded.SOLUTION: A workpiece W1 which is formed by interposing a solder paste 40 between a first member 10 and a second member 20 is prepared. A manufacturing method includes: a preheating process of heating the workpiece W1 at a first temperature T2 higher than a normal temperature; a main heating process of melting solder 30 by heating the workpiece W1 at a second temperature T3 higher than the first temperature T2; and a cooling process of cooling and solidifying the molten solder 30. The manufacturing method includes a viscosity adjusting process, before the preheating process, of maintaining the workpiece W1 at the third temperature T1 lower than the first temperature T2 so that an outer surface 40a side contacting with outside air becomes highly-viscous than an inner side of the solder paste 40.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a manufacturing method for manufacturing a solder joined body in which a first member and a second member are joined by soldering, and particularly relates to soldering using a solder paste.

  Conventionally, for example, a method described in Patent Document 1 has been proposed as a method for manufacturing this type of solder joint. In this manufacturing method, a work is first prepared between a first member and a second member by interposing a solder paste containing a solvent in solder (preparation step). Here, the solder paste is a mixture of powdered solder and flux, and the flux contains a base resin, a solvent, an activator, and the like.

  The workpiece is heated at a first temperature (normally 100 ° C. or higher) higher than normal temperature (preheating step), and then the workpiece is heated at a second temperature higher than the first temperature to be soldered. Is melted (main heating step). Thereafter, the molten and reflowed solder in the workpiece is cooled and solidified to form a solder joined body in which the first member and the second member are joined by soldering (cooling step).

JP 2002-178140 A

  As described above, in the solder paste supplied in advance between both members, preheating is performed before the solder is melted. At this time, when the solder is melted, the solvent contained in the flux bumps, May be scattered.

  Here, a substrate is often used as the first member or the second member, but a bonding land or the like on this substrate is a region where solder is not attached. If such a region is present in the first member or the second member, it becomes a defective product when the molten solder is scattered and adhered.

  Here, simply, in order to prevent such solder scattering, it is considered that the preheating time should be longer than usual and the entire solder paste should be in a high viscosity state. However, if the preheating time before melting of the solder (that is, before the main heating step) is too long, depending on the preheating temperature, the solder itself is oxidized and the wettability of the paste is lowered, resulting in many voids in the solder. There is a risk.

  The present invention has been made in view of the above-described problems, and in the manufacture of a solder joined body in which the first member and the second member are joined by solder, prevention of solder scattering generated during solder joining, and An object of the present invention is to provide a manufacturing method suitable for suppressing the generation of voids in solder.

In order to achieve the above object, according to the first aspect of the present invention, a solder paste comprising a solder (30) containing a solvent between the first member (10) and the second member (20) ( 40) preparing a workpiece (W1) intervening, a preheating step of heating the workpiece at a first temperature (T2) higher than room temperature, and then the workpiece from the first temperature. The main heating step in which the solder is melted by heating at a higher second temperature (T3), and the melted solder in the workpiece is cooled and solidified, whereby the first member and the second member are joined by soldering. A cooling step for forming a solder joint, and a method for producing a solder joint comprising:
Prior to the preheating step, the workpiece is held at a third temperature (T1) lower than the first temperature so that the outer surface (40a) side in contact with the outside air in the solder paste is in a state of higher viscosity than the inner side. A viscosity adjusting step is provided.

  According to this, in the viscosity adjustment step before the preheating step, the solder paste is maintained at a third temperature lower than the first temperature in the preheating step, so that the solvent on the outer surface side in the paste is volatilized, and the paste Has a higher viscosity on the outer surface side than on the inner side. In this state, since the viscosity of the outer surface of the paste increases, it is possible to prevent solvent boiling and solder scattering.

  Moreover, since the inside of the paste can be in a low-viscosity state in which the solvent is sufficiently contained, the wettability of the solder paste is sufficiently ensured. Thus, according to the present invention, it is possible to provide a manufacturing method suitable for preventing solder scattering that occurs during solder joining and suppressing the generation of voids in the solder.

  Moreover, in the manufacturing method of Claim 1, like the invention of Claim 2, in a viscosity adjustment process, a solder paste is made before a viscosity adjustment process by hold | maintaining a workpiece | work to 3rd temperature. It is preferable that the weight reduction rate of the solvent is 3% or more and 7% or less with respect to the weight of the solvent in the solder paste.

  In addition, the code | symbol in the bracket | parenthesis of each means described in the claim and this column is an example which shows a corresponding relationship with the specific means as described in embodiment mentioned later.

It is a schematic sectional drawing which shows the solder joint body concerning embodiment of this invention. It is a schematic sectional drawing which shows the preparation process in the manufacturing method of the solder joined body shown by FIG. It is a figure which shows the schematic temperature profile of the viscosity adjustment process in the manufacturing method of the soldering body shown by FIG. 1, a preheating process, and this heating process. It is a figure which shows typically the solder paste concerning the said embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following drawings, parts that are the same or equivalent to each other are given the same reference numerals in the drawings for the sake of simplicity.

  The solder joint S1 according to the first embodiment of the present invention will be described with reference to FIG. This solder joint S1 is mounted on a vehicle such as an automobile, for example, and is applied as an electronic device for driving various devices for the vehicle.

  The solder joint body S1 of the present embodiment is broadly joined between the first member 10, the second member 20, and the first member 10 and the second member 20 to join both members. And solder 30 to be configured.

  Examples of the first member 10 include, but are not limited to, solder mounted components such as a semiconductor chip, a transistor element, a flip chip element, a mold package, a resistance element, and a capacitor element. Examples of the second member 20 include, but are not limited to, a wiring board, a lead frame, a heat sink, and a bus bar. In the illustrated example, the first member 10 is a semiconductor chip, and the second member 20 is a printed board.

  Furthermore, both the first member 10 and the second member 20 may be metal members such as metal terminals, for example. In short, both the first member 10 and the second member 20 may be members that can be soldered together.

  As the solder 30, a known solder can be used. For example, Sn-Ag series, Sn-Cu series, Sn-Ag-Cu series alloys, Sn-Pb series alloys and the like can be mentioned, but Pb-free ones are desirable. As will be described later, the solder 30 is installed in a solder paste state and used for soldering.

  Next, a method for manufacturing the solder joint S1 will be described with reference to FIGS. First, as shown in FIG. 2, as a preparation process, a work W <b> 1 is prepared in which a solder paste 40 containing a solvent in solder is interposed between the first member 10 and the second member 20. To do.

  Here, as shown in FIG. 2, the solder paste 40 is disposed on the second member 20 by a known method such as printing, dispensing, and transfer (see FIGS. 2A and 2B). Then, by mounting the first member 10 thereon, the solder paste 40 is interposed between both the members 10 and 20 to form the workpiece W1 (see FIG. 2C). Here, the outer peripheral end surface of the solder paste 40 is an outer surface 40a that is exposed to the outside air between both the members 10 and 20 and is in contact with the outside air.

  Such a solder paste 40 is obtained by adding a solvent to solder. Specifically, as shown in FIG. 4, like the known one, a powdered solder 30 and a solvent are added. It is comprised as a mixture with the flux 41 containing. Although not limited, for example, the solder 30 is 80 to 90 wt% and the flux 41 is 10 to 20 wt% with respect to the entire paste.

  First, as the solder 30, as described above, a known solder can be used. Specific examples of the solder 30 in the solder paste 40 include, but are not limited to, a powder of Sn—Ag, Sn—Cu, Sn—Ag—Cu, Sn—Pb, and the like. It is done. Of course, a Pb-free material is also desirable in this case.

  Further, the flux 41 is also a well-known one, and exhibits the following functions (1), (2), and (3). (1) An oxide removing action that removes oxides and the like that inhibit the wetting of the base material and the solder. (2) Anti-reoxidation action that blocks air and prevents re-oxidation of solder due to heating. (3) A surface tension reducing action that reduces the surface tension of the solder and helps the solder to wet.

  The flux 41 includes a base resin that removes an oxide film on the metal surface, an activator that improves cleaning ability and wettability, a solvent that adjusts the viscosity, and an antioxidant, a thixotropic agent, and the like as necessary. It is configured as a mixed mixture. Although not limited here, the base resin is 30 to 40% by weight, the activator is 1 to 5% by weight, and the solvent is 40 to 50% by weight with respect to the entire flux 41.

  Moreover, although not limited, what is normally used about the above-mentioned base resin, an activator, and a solvent is mentioned. Examples of the base resin include rosin and various rosin derivatives. Examples of the activator include organic hydrohalides, organic acids, organic halogens and the like. Examples of the solvent include alcohols, glycol ethers, esters, hydrocarbons and the like. The solvent is a component that is particularly volatile in the flux 41.

  Next, the workpiece W1 is soldered with the temperature profile shown in FIG. In the soldering of the present embodiment, similarly to the known method, the preheating step of heating the workpiece W1 at the first temperature T2 higher than the normal temperature, and heating the workpiece W1 at the second temperature T3 higher than the first temperature T2. And a main heating step for melting the solder and a cooling step for cooling and solidifying the molten solder in the workpiece W1.

  Furthermore, in the soldering of this embodiment, it is set as the original method provided with the viscosity adjustment process before the preheating process. In the viscosity adjusting step, the workpiece W1 is held at the third temperature T1 lower than the first temperature T2 so that the outer surface 40a side of the solder paste 40 has a higher viscosity than the inner side.

  A state realized by this viscosity adjusting step, that is, a state where the outer surface 40a side of the solder paste 40 has a higher viscosity than the inner side is hereinafter referred to as an “outer high viscosity state”. This outer high-viscosity solder paste 40 is shown in FIG. As shown in FIG. 4, the outer surface 40 a side of the flux 41 is a high viscosity portion 42, and the inner side is a low viscosity portion 43.

  Temperature adjustment such as temperature increase and temperature decrease in the viscosity adjustment process, preheating process, main heating process, and cooling process is typically performed using a reflow furnace for solder reflow. A hot plate or the like may be used. FIG. 3 shows the timing of putting the workpiece W1 into the reflow furnace in the present embodiment.

  Here, the third temperature T1 at which the solder paste 40 is in the outer high viscosity state in the viscosity adjusting step is determined in advance. As a method for confirming the outer high viscosity state in the solder paste 40, for example, a puncture strength test generally performed on a resin film or the like may be applied.

  Specifically, a droplet of the solder paste 40 is dropped on the substrate, and this state is maintained at a predetermined temperature (for example, the state shown in FIG. 2B). Thereafter, the outer surface of the paste is pierced with a pin or the like, and the load on the outer surface at that time and the load in the interior that has passed through the outer surface may be obtained.

  The relative magnitude relationship between the viscosity on the outer surface side and the viscosity on the inner side in the solder paste 40 is discriminated based on the magnitude of both loads, and the outer high viscosity state can be confirmed. And the temperature for the solder paste 40 to be in the outer high viscosity state is obtained, and this may be adopted as the third temperature T1.

  The third temperature T1 is lower than the first temperature T2 in the preheating step and is typically equal to or higher than room temperature. However, if the temperature is such that the solder paste 40 is in an outer high-viscosity state, May be low. Here, normal temperature is 20 ° C to 30 ° C. When the third temperature T1 is equal to or lower than the normal temperature, the viscosity adjustment step does not need to use the heating device described above. When the third temperature T1 is lower than the normal temperature, a method such as leaving it in a cold place may be used.

  Furthermore, the third temperature T1 is desirably lower than 100 ° C., which is the temperature of the normal preheating process, that is, the upper limit is less than 100 ° C., and typically 30 ° C. to 50 ° C. is desirable. Moreover, although it does not limit the time hold | maintained at 3rd temperature T1, it shall be about 5 minutes-30 minutes. For example, in the example of FIG. 3, the third temperature T1 is a constant temperature of 40 ° C., and the time is about 10 minutes.

  Thus, if the solder paste 40 is in the outer high viscosity state by the viscosity adjusting step, the temperature is raised to the first temperature T2 and the preheating step is performed to preheat the solder paste 40. Thereafter, the temperature is further raised to the second temperature T2 to move to the main heating step, and the solder 30 in the solder paste 40 is melted.

  Here, although not limited, in the example of FIG. 3, in the preheating step, for example, the first temperature T2 is set to 130 ° C. to 150 ° C. and the time is set to about 1 minute to 2 minutes. The temperature T3 of 2 is set to 220 to 250 ° C., and the time is set to about 1 minute. As described above, the solder paste 40 in the present embodiment is a known one as shown in the above specific example, and the above specific examples of temperature and time in each process are suitable for this.

  Then, after the main heating step, the temperature is lowered to move to the cooling step. The melted solder 30 is solidified by this cooling step, solder joining is completed, and a solder joint S1 in which the first member 10 and the second member 20 are solder-joined is formed.

  In FIG. 3, a temperature profile in the conventional soldering is shown by a broken line as a comparative example. In this embodiment and the comparative example, the timing of putting the workpiece W1 into the reflow furnace is different, but the preheating step, the main heating step, and the cooling step are substantially the same.

  However, as shown in FIG. 3, the previous step of the preheating step in the prior art is a temperature raising step for raising the temperature to the temperature of the preheating step, whereas the viscosity adjusting step in the example of FIG. The temperature T1 is kept at a constant temperature without fluctuation such as a temperature rise for a certain time. That is, the viscosity adjustment process shown in FIG. 3 is completely different from the conventional temperature raising process as a pre-process of the preheating process.

  However, in the present embodiment, it is not excluded that the third temperature T1 fluctuates with a certain width. That is, in the viscosity adjusting step, the third temperature T1 may be changed.

  By the way, according to this embodiment, in the viscosity adjustment step before the preheating step, the solder paste 40 is held at the third temperature T1 lower than the first temperature T2 in the preheating step, so that the outer surface in the paste The solvent on the 40a side volatilizes, and the paste has a higher viscosity on the outer surface 40a side than on the inner side. In this state, since the viscosity of the outer surface 40a of the paste increases, it is possible to prevent bumping of the solvent and scattering of the solder.

  Here, FIG. 4 schematically shows the state of solder scattering suppression according to the present embodiment. As described above, as shown in FIG. 4, the flux 41 in the solder paste 40 is divided into a low-viscosity portion 43 inside the paste and a high-viscosity portion 42 on the outer surface 40a side of the paste by the viscosity adjustment step. It becomes.

  When the preheating step and the main heating step are performed in this state, as shown in FIG. 4, a portion where the solvent is vaporized, that is, a solvent vaporization portion K <b> 1 is generated inside the paste where the solvent is sufficiently present. Then, the solder 30 moves to the outer surface 40a side of the paste by the expanding pressure of the solvent vaporizing portion K1. However, in the present embodiment, since the outer surface 40a side of the paste is the high viscosity portion 42, scattering of the moving solder 30 to the outside is easily suppressed.

  Moreover, since the inside of the paste can be in a low-viscosity state in which the solvent is sufficiently contained, the wettability of the solder paste 40 is sufficiently ensured.

  Further, in the viscosity adjusting step, it is only necessary to volatilize the solvent substantially only on the outer surface 40a side of the solder paste 40. Therefore, the third temperature T1 is significantly lower than the first temperature T2 in the preheating. can do. This is preferable in terms of preventing the solder 30 from being oxidized in the paste and suppressing a decrease in wettability.

  As described above, according to the present embodiment, in manufacturing the solder joint S1 in which the first member 10 and the second member 20 are solder-bonded, the solder 30 is prevented from being scattered at the time of soldering, and A manufacturing method suitable for suppressing the generation of voids in the solder 30 can be provided.

  Further, in the viscosity adjusting step, the solvent on the outer surface 40a side is volatilized and the solder paste 40 is in the outer high viscosity state. That is, this means that the weight of the solvent in the paste is reduced before and after the viscosity adjustment step.

  In order to realize such an outer high-viscosity state, in the viscosity adjusting step, the work W1 is held at the third temperature T1, so that in the solder paste 40, the amount of solvent relative to the weight of the solvent before the viscosity adjusting step. It is desirable that the weight reduction rate be 3% or more and 7% or less. With such a weight reduction rate, the solvent on the outer surface 40a side of the solder paste 40 is mainly volatilized, and the amount of the solvent in the paste does not change so much.

  Here, the weight reduction rate of the solvent becomes 3% or more and 7% or less with respect to the weight of the solvent in the solder paste 40 before the viscosity adjusting step, in other words, in the paste before the viscosity adjusting step. The solvent is volatilized and the weight of the solvent after volatilization is reduced to 93% or more and 97% or less before the viscosity adjustment step. Such a change in the weight of the solvent can be measured by a method such as a known TG method (Thermo Gravimetry).

(Other embodiments)
The first member 10 and the second member 20 may be any members that can be soldered together, and are not limited to the specific examples described above. Further, the solder 30 may be any solder as long as it is installed in the state of the solder paste 40 and used for soldering, and is not limited to the specific example described above.

  Further, the solder 30 and the flux 41 in the solder paste 40 are not limited to the specific examples described above.

  For example, when the second member 20 is a wiring board and the first member 10 is a semiconductor chip, a plurality of first members 10 are soldered to the second member 20. There may be.

  Further, the present invention is not limited to the above-described embodiment, and can be appropriately changed within the scope described in the claims. The above embodiments are not irrelevant to each other, and can be combined as appropriate unless the combination is clearly impossible, and the above embodiments are not limited to the illustrated examples. Absent. In each of the above-described embodiments, it is needless to say that elements constituting the embodiment are not necessarily essential unless explicitly stated as essential and clearly considered essential in principle. Yes. Further, in each of the above embodiments, when numerical values such as the number, numerical value, quantity, range, etc. of the constituent elements of the embodiment are mentioned, it is clearly limited to a specific number when clearly indicated as essential and in principle. The number is not limited to the specific number except for the case. Further, in each of the above embodiments, when referring to the shape, positional relationship, etc. of the component, etc., the shape, unless otherwise specified and in principle limited to a specific shape, positional relationship, etc. It is not limited to the positional relationship or the like.

DESCRIPTION OF SYMBOLS 10 1st member 20 2nd member 30 Solder 40 Solder paste 40a Outer surface of solder paste T1 3rd temperature T2 1st temperature T3 2nd temperature W1 Workpiece

Claims (3)

A preparation step of preparing a work (W1) in which a solder paste (40) containing a solvent in solder (30) is interposed between the first member (10) and the second member (20). When,
A preheating step of heating the workpiece at a first temperature (T2) higher than room temperature;
Next, a main heating step in which the workpiece is heated at a second temperature (T3) higher than the first temperature to melt the solder,
Cooling the solidified solder in the workpiece to form a solder joined body in which the first member and the second member are joined by soldering, thereby producing a solder joined body. A method,
Before the preheating step, the solder paste has a third temperature (T1) lower than the first temperature such that the outer surface (40a) side in contact with the outside air has a higher viscosity than the inner side. A method for producing a solder joint comprising a viscosity adjusting step for holding a workpiece.   In the viscosity adjusting step, by holding the workpiece at the third temperature, the weight reduction rate of the solvent is reduced with respect to the weight of the solvent in the solder paste before the viscosity adjusting step. The method for producing a solder joint according to claim 1, wherein the state is 3% or more and 7% or less.   3. The method of manufacturing a solder joint according to claim 1, wherein the third temperature is 30 ° C. or higher and 50 ° C. or lower.

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