JPH07268651A - Reflowed solder plated square wire and its production - Google Patents

Abstract

PURPOSE:To obtain a reflowed solder plated square wire excellent in corrosion resistance, solderability, bendability and wear resistance. CONSTITUTION:When b square Cu or Cu alloy wire electroplated with an Sn-Pb alloy solder layer is subjected to prescribed reflowing treatment to obtain a reflowed solder plated square wire, the Snob Pb alloy-solder layer is made of a polycrystalline body of Snwith Pb 1 deposited on grain boundaries. Since the crystal structure of the solder plating layer is made of a polycrystalline body of Sn with Pb deposited on grain boundaries and bonding between grains is strengthened, the effect of a Cu-Sn compd. layer formed by the reflowing treatment on bendability, solderability and wear resistance is eliminated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflow solder-plated square wire excellent in corrosion resistance, solderability, bendability, and wear resistance, and a method for manufacturing the same.

[0002]

2. Description of the Related Art Copper or copper alloy wire coated with Sn or Sn alloy is a material having the conductivity and strength of copper or copper alloy.
It is a high performance conductor in which the corrosion resistance and solder bondability of the n or Sn alloy coating layer are well meshed, and is widely used for terminals, connectors, lead wires, electric cables and the like. Then, a punching material of a copper alloy strip coated with Sn or a Sn alloy was used for the connector and the like, but a pin type connector (pin grid array, etc.) that does not produce punching scraps was developed, Solder-plated square wire was used.

An inexpensive hot dip plating method is partially used for solder plating on a copper square wire. This method has a large uneven thickness, and the copper-tin compound layer is formed thick, resulting in poor bendability and solderability. The bright electroplating method is widely used because it has an advantage that a thin plating layer having a uniform thickness can be obtained. However, this bright electroplating method has the following drawbacks. Since a brightening agent that brightens the surface and a smoothing agent that smoothes the surface are added to the electrolytic solution, these additives are sucked into the crystal grain boundaries of the plating layer, weakening the bond between the crystal grains, and Copper freely diffuses to form a thick copper-tin compound layer, which reduces the bendability and solderability of the solder-plated square wire. The brightening agent makes the crystal grains finer to increase the grain boundary strain and promotes the diffusion of copper. The refinement of the crystal grains accelerates the discoloration caused by the crystal grain boundaries as nuclei, and the additives remaining on the crystal grain boundaries and the surface accelerate the discoloration. The weakening of the bonding force between the crystal grains also causes the plating layer to come into contact with a jig or the like during processing to generate solder powder, which lowers the manufacturing yield and the wear resistance of the product. Whiskers are likely to occur.

[0004]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
Electroplating without adding brightener, only smoothing agent,
A method has been developed in which electroplating is followed by reflow treatment to give gloss. The reflow process is a process to continuously pass a copper square wire electroplated with solder through a running furnace to melt the solder plating layer and make the solder plating layer glossy, while at the same time relaxing internal stress and smoothing it. The agent is also removed by thermal decomposition and the crystal grains are coarsened. However, in this reflow treatment, the copper-tin compound layer was thickly formed by heating during the reflow treatment, and the bendability and solderability of the reflow solder-plated square wire were hindered.
Also, a small amount of solder powder was generated during manufacturing. In addition, the reflow process causes the solder at the corners of the square wire to flow to the flat surface and make it thinner,
Here, there arises a problem that the Cu of the square wire diffuses to the surface of the solder layer and is discolored.

[0005]

[Means for Solving the Problems] Under such circumstances, earnest research was conducted, and the solderability, bendability, and abrasion resistance (generation of solder powder) of the reflow treated material depended on the crystal structure of the solder plating layer. Therefore, the present invention has been completed through further research. That is, the invention of claim 1 is a reflow solder-plated square wire obtained by subjecting a copper or copper alloy square wire electroplated with an Sn-Pb alloy solder layer to a predetermined reflow treatment,
The n-Pb alloy solder layer is a reflow solder-plated square wire, characterized in that it is made of a polycrystal of Sn in which Pb is precipitated at grain boundaries.

The square wire according to the present invention reduces the solderability, bendability, and abrasion resistance (generation of solder powder) due to the copper-tin compound layer formed by the reflow treatment and reduces the crystal structure of the solder plating layer. This is prevented by forming a structure in which Pb is precipitated in the Sn crystal grain boundary. The crystal structure of the solder plating layer of the reflow solder-plated square wire of the present invention is a structure in which Pb phase 1 is precipitated at the Sn crystal grain boundary as shown in FIG. On the other hand, the conventional reflow solder plating square wire has a structure in which spherical Pb phases 1 are randomly deposited in Sn crystal grains 2 as shown in FIG.

In the present invention, the reflow solder plating layer having the crystal structure shown in FIG. 1 improves the solderability, bendability, and abrasion resistance. By increasing the average value of the Sn crystal grain size of the solder plating layer to 2 μm or more, the crystal grain boundaries are reduced, the grain boundary diffusion amount of Cu is accordingly reduced, and the copper tin compound layer is thinly formed. The thickness of the copper-tin compound layer formed at the interface between the solder plating layer and the square wire is 0.
By setting the thickness to 45 μm or less, bendability is significantly improved.

The solder plating layer is temporarily melted by the reflow process. At this time, if the molten state lasts for a long time or if the square wire vibrates violently during melting, the molten solder may flow from the corner portion to the flat portion due to the surface tension, and the plating layer thickness at the corner portion may become thin. is there. In this case, since the corner portion has a thin plating layer, it is oxidized and discolored by humidification or heating, or the compound layer is exposed, so that the solderability is deteriorated. Therefore, it is desirable that the thickness deviation k of the plating layer be 1.5 or less. However, the thickness deviation k is defined by the following equation. Thickness deviation k = (maximum thickness of solder plating layer measured by fluorescent X-ray film thickness meter) / (average thickness of solder plating layer measured by constant current anodic dissolution method). still,
The fluorescent X-ray film thickness meter has a collimator diameter of 0.1 mm.

In the present invention, as the Sn-Pb alloy solder, a normal Sn-Pb alloy solder containing 5 to 60 wt% of Pb is applied. For the copper alloy square wire, a brass material excellent in corrosion resistance and mechanical properties, or a spring material such as phosphor bronze, beryllium copper, Corson alloy, nickel silver is suitable. These alloy wires are subjected to undercoating with Cu, if necessary, and then subjected to solder plating and reflow treatment.

A fifth aspect of the present invention is a method for manufacturing a reflow solder-plated square wire according to the first aspect of the invention. That is, Sn-P
In a method for producing a reflow solder-plated square wire, a copper or copper alloy square wire electroplated with a b-alloy solder layer is run in a furnace heated to a predetermined temperature at a predetermined speed for reflow treatment,
The traveling speed of the copper or copper alloy square wire plated with the solder layer in the furnace is 80 to 96% of the lower limit speed at which the solder layer is in an unmelted state.
It is characterized by setting the speed to.

In the present invention, the lower limit speed at which the solder layer is in the unmelted state is the lower limit speed at which the solder layer is in the unmelted state when the running speed is gradually increased from the melting speed of the solder layer. In the present invention, the reason why the traveling speed in the furnace of the copper or copper alloy square wire plated with the solder layer is limited to 80 to 96% of the lower limit speed at which the solder layer is in an unmelted state is even less than 80%. Further, even if it exceeds 96%, the crystal structure of the solder plating layer does not become the structure in which Pb is precipitated in the crystal grain boundary of Sn. On the other hand, if it is less than 80%, the Pb layer at the corner portion of the square wire flows to the flat surface portion and becomes thin, Cu of the square wire diffuses to the solder layer surface at the corner portion, and discoloration occurs.

[0012]

In the reflow solder-plated square wire of the present invention, since the crystal structure of the solder-plated layer is made of a polycrystal of Sn in which Pb is precipitated at the grain boundaries, the bond between the crystal grains is strengthened and the bending process is performed. Generation of cracks and abrasion powder due to contact with the jig are prevented. Since Pb that does not react with Cu is deposited on the grain boundaries that serve as the diffusion path of Cu, the diffusion of Cu is suppressed and the copper-tin compound layer is formed thin. As a result, bendability is improved, and deterioration of solderability at high temperatures is prevented. This effect becomes more remarkable as the average grain size of the solder plating layer becomes 2 μm or more and the grain boundary area becomes smaller. Since the above-mentioned copper-tin compound layer is hard, it causes cracks. Its thickness is 0.45
By setting the thickness to be less than μm, the bendability is significantly improved.
By setting the traveling speed of the solder plating square wire in the reflow treatment to a speed of 80 to 96% of the lower limit speed at which the solder layer is in an unmelted state, a structure in which Pb is precipitated at the grain boundaries of the Sn polycrystalline body is obtained, Bendability and solderability are improved. In addition, the thickness deviation of the corners of the square wire is 1.5 or less, and discoloration under humidification and heating is prevented.

[0013]

Example A brass wire of 0.5 mm square was electroplated with 9/1 solder, and this was reflow-treated to manufacture a reflow solder-plated square wire. The outline of the apparatus used is shown in FIG. In the figure, 4
Is a brass square wire, 9 is a solder plating bath for plating a solder layer on the brass square wire, and 11 is a running furnace for reflowing the solder layer. The brass square wire 4 supplied from the uncoiler 3,
The electrolytic degreasing tank 5, the water washing tank 6, the pickling tank 7, and the water washing tank 16 are sequentially passed through to perform a pretreatment for plating, and then a Cu plating tank 8 is used for C treatment.
u was plated to a thickness of 1.0 μm, washed with water in a washing bath 26, and then electroplated with solder to a thickness of 2.0 μm in a solder plating bath 9. Next, this is washed with water in a washing tank 36, and a hot air dryer 10
After drying, reflow process is performed in the running furnace 11 and cooling water tank
After cooling at 12, it was wound around a coiler 13. The solder plating was performed using a borofluoric acid-based electrolytic solution containing a smoothing agent. The reflow processing conditions were variously changed.

The reflow solder-plated square wires thus obtained were examined for corrosion resistance, solderability, bendability, and wear resistance. The corrosion resistance was evaluated by the accelerated deterioration test under the following conditions and the presence or absence of discoloration after the test. The solderability was investigated under the following conditions using the sample after the accelerated deterioration test. The bendability was evaluated by observing the surface cracks after self-diameter winding with a stereoscopic microscope at a magnification of 1000 times and observing the cracks. For the abrasion resistance, a Bowden type abrasion tester was used to examine the generation state of solder powder. A reflow tin-plated strip press-processed at the tip 5R was used for the sliding probe, and 100 reciprocations were performed under the conditions of a sliding distance of 50 mm and a load of 50 gf. The results are shown in Table 2. Table 1 shows the crystal grain size of Sn and Pb.
The deposition state, the thickness deviation of the solder plating layer, and the thickness of the copper-tin compound layer are shown. Accelerated deterioration test: Humidity resistance test, temperature 105 ℃, relative humidity 100%
RH, leaving time 24 hours. Atmospheric heating test, temperature 155 ℃, leaving time 24 hours. Solderability test (meniscograph method): Eutectic solder used, temperature 230
℃, flux 25% rosin / methanol, dipping speed 2mm
/ sec, immersion depth 2 mm, immersion time 10 sec, evaluation zero cross time.

[0015]

[Table 1]

[0016]

[Table 2]

As is clear from Tables 1 and 2, the products of Examples of the present invention (Nos. 1 to 8) exhibited good characteristics in all of corrosion resistance, solderability, bendability, and abrasion resistance. . Of these, No. 7 is
Since the crystal grain size of Sn was slightly small at 1.6 μm, the crystal grain boundaries increased and the solderability and wear resistance were slightly reduced. or
Since No. 8 had a relatively large thickness deviation of 1.6, the Cu of the brass square wire partially diffused on the surface of the corner where the solder layer was thin, causing a slight discoloration. In addition, the thickness of the compound layer becomes slightly thicker,
The workability deteriorated, and the bendability and wear resistance were somewhat reduced.

On the other hand, in Comparative Examples Nos. 9 to 12, any of corrosion resistance, solderability, bendability, and abrasion resistance was deteriorated. In the appearance after the moisture resistance test, yellow discoloration was seen in the No. 11 and 12 samples. This is because the crystal grains have a small diameter (No. 11 and 12), and in particular No. 12, the discoloration was large due to the adsorption of the additive. Regarding solderability after the moisture resistance test, there was no significant difference in the No. 9 to 12 soldering time (zero cross time) of about 1 second. Even in the discolored Nos. 11 and 12, the Sn oxide formed on the surface was easily dissolved in the molten solder in a short time, so that the solderability was not deteriorated.

Regarding the surface appearance after heating in the atmosphere, in Nos. 9 to 10, since the solder at the corners flowed to the flat surface and the solder thickness at the corners decreased (the thickness unevenness was large), this thin solder layer portion was , Reacts with Cu of the square wire diffused by heating to produce a copper tin compound,
This was exposed and the corners turned gray. In Nos. 11 and 12, the crystal grain size of the solder is dense and the gaps between the crystal grains are wide, so the Cu of the square wire diffuses at high speed and the entire solder layer becomes a copper tin compound layer, and the entire surface turns gray. did. Solderability after heating to the atmosphere is
In Nos. 9 to 12, the copper tin compound was exposed on the surface, so the wetting time was significantly lengthened.

In the self-diameter winding test (bendability), No. 9 and 10
In No. 11 and 12, the copper-tin compound layer was thick, and in No. 11 and 12, the solder layer was not melted, and the degree of adhesion between crystal grains was weak.

In the abrasion test, generation of solder powder was found in all of Nos. 9-12. The cause of generation of solder powder in Nos. 9 and 10 is unknown, but it is considered that the hard intermetallic compound layer became thick and tough, and the solder plating layer was easily scraped. In Nos. 11 and 12, the weakening of the bonding force between the crystal grains is the cause.

[0022]

As described above, the reflow solder-plated square wire of the present invention has improved corrosion resistance, solderability, bendability, and wear resistance, and the solder-plated copper square wire is subjected to reflow treatment under predetermined conditions. By doing so, it can be produced, and has a remarkable industrial effect.

[Brief description of drawings]

FIG. 1 is a crystal structure diagram of a solder plating layer of a reflow solder plating square wire of the present invention.

FIG. 2 is a schematic view of a method for manufacturing a reflow solder-plated square wire according to the present invention.

FIG. 3 is a crystal structure diagram of a solder plating layer of a conventional reflow solder plating square wire.

[Explanation of symbols]

 1─────Pb phase 2─────Sn crystal grains 3───── Uncoiler 4───── Brass square wire 5───── Electrolytic degreasing tank 6,16,26,36 ─ Washing tank 7 ───── Pickling tank 8 ───── Cu plating tank 9 ───── Solder plating tank 10 ───── Hot air dryer 11 ───── Running furnace 12─ ──── Cooling water tank 13 ───── Coiler

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yuji Suzuki 2-6-1 Marunouchi, Chiyoda-ku, Tokyo Furukawa Electric Co., Ltd.

Claims (5)

[Claims] 1. A reflow solder-plated square wire obtained by subjecting a copper or copper alloy square wire electroplated with an Sn-Pb alloy solder layer to a predetermined reflow treatment, wherein the Sn-Pb alloy solder layer has Pb at grain boundaries. A reflow solder-plated square wire, which is made of a deposited Sn polycrystal. 2. The reflow solder-plated square wire according to claim 1, wherein the average grain size of Sn in the solder-plated layer is 2 μm or more. 3. The reflow solder according to claim 1, wherein the thickness of the intermetallic compound layer formed at the interface between the copper or copper alloy square wire and the solder plating layer is 0.45 μm or less. Plated square wire. 4. The reflow solder-plated square wire according to claim 1, wherein the thickness deviation k of the solder plating layer is 1.5 or less. However, k = (maximum thickness of solder plating layer measured by fluorescent X-ray film thickness meter) / (average thickness of solder plating layer measured by constant current anode melting method). However, the collimator diameter of the fluorescent X-ray film thickness meter is 0.1 mm. 5. A method for producing a reflow solder-plated square wire, comprising: reflowing copper or copper alloy square wire electroplated with a Sn-Pb alloy solder layer in a furnace heated to a predetermined temperature at a predetermined speed. The reflow according to claim 1, wherein the traveling speed of the copper or copper alloy square wire plated with the solder layer in the furnace is set to 80 to 96% of the lower limit speed at which the solder layer is in an unmelted state. Manufacturing method of solder-plated square wire.