JP2749773B2 - Reflow solder plating square wire and method of manufacturing the same - Google Patents

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, bending property and abrasion resistance, and a method for producing the same.

[0002]

2. Description of the Related Art A copper or copper alloy wire coated with Sn or a Sn alloy is made of a material such as copper or copper alloy having conductivity and strength.
It is a high-performance conductor in which the corrosion resistance and the solder bonding property of the n or Sn alloy coating layer are well interlocked, and is widely used for terminals, connectors, lead wires, electric cables and the like. A punched material of a copper alloy strip coated with Sn or Sn alloy has been used for the connector and the like. However, a pin type connector (a pin grid array or the like) which does not produce punched debris has been developed. Solder-plated square wires have been used.

In order to perform solder plating on copper square wires, an inexpensive hot-dip plating method is used in part. This method has a large uneven thickness and a thick copper-tin compound layer, resulting in inferior bendability and solderability. The bright electroplating method has an advantage that a thin plating layer having a uniform thickness can be obtained, and is often used. However, this bright electroplating method has the following disadvantages. Since a brightening agent for brightening the surface and a smoothing agent for smoothing the surface are added to the electrolytic solution, these additives are sucked into the crystal grain boundaries of the plating layer to weaken the bonding between the crystal grains, and this grain boundary is reduced. Copper is freely diffused to form a thick copper-tin compound layer, and the bendability and solderability of the solder-plated square wire are reduced. The brightening agent refines the crystal grains and increases the grain boundary strain, thereby promoting copper diffusion. Refinement of crystal grains promotes discoloration that occurs at crystal grain boundaries as nuclei, and additives that remain on crystal grain boundaries and surfaces accelerate color change. The weakening of the bonding force between the crystal grains causes the plating layer to come into contact with a jig or the like during processing, thereby generating solder powder, lowering the production yield and lowering the abrasion resistance of the product. Whiskers are likely to occur.

[0004]

SUMMARY OF THE INVENTION
Do not use brightener, add only smoothing agent and electroplate,
A method has been developed in which a gloss is obtained by reflow treatment after electroplating. The reflow process is a process to melt the solder plating layer by continuously passing a copper square wire with electroplated solder through a running furnace to make the solder plating layer glossy. The agent is removed by thermal decomposition and the crystal grains are coarsened. However, in this reflow treatment, the copper-tin compound layer was formed thick by the heating during the reflow treatment, and the bendability and solderability of the reflow solder plating square wire were hindered.
Also, a small amount of solder powder was generated during the production. In the reflow process, the solder at the corners of the corner line flows to the flat part and becomes thinner,
Here, there was a problem that Cu of the square wire diffused to the surface of the solder layer and discolored.

[0005]

In order to solve the problem, we have conducted intensive research and found that the solderability, bendability, and abrasion resistance (solder powder generation) of the reflow treated material depend on the crystal structure of the solder plating layer. The inventor found that the present invention was completed, and further research was carried out to complete the present invention. That is, the invention of claim 1 is a reflow solder-plated square wire in which a predetermined reflow process is performed on a copper or copper alloy square wire on which an Sn—Pb alloy solder layer is electroplated.
The reflow solder plating square wire, wherein the n-Pb alloy solder layer is made of a polycrystalline Sn having Pb precipitated at a grain boundary.

The square line of the present invention can be used to reduce the solderability, bendability, and abrasion resistance (generation of solder powder) due to the copper-tin compound layer formed by the reflow treatment, and to reduce the crystal structure of the solder plating layer. This is prevented by forming a structure in which Pb is precipitated at the grain boundaries of Sn. The crystal structure of the solder plating layer of the reflow solder plating square wire of the present invention is a structure in which the 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 a spherical Pb phase 1 is randomly precipitated in Sn crystal grains 2 as shown in FIG.

In the present invention, the reflow solder plating layer has the crystal structure shown in FIG. 1 to improve 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 Cu grain boundary diffusion amount is reduced, and a thin copper-tin compound layer is formed. The thickness of the copper tin compound layer generated at the interface between the solder plating layer and the square wire is 0.
By setting the thickness to 45 μm or less, the bendability is greatly improved.

[0008] The solder plating layer is temporarily melted by the reflow process. At this time, if the molten state lasts for a long time or the square wire vibrates violently during melting, the molten solder may flow from the corner to the flat part due to the surface tension and the plating layer thickness at the corner may become thin. is there. In this case, since the plating layer is thin at the corner, oxidative discoloration or exposure of the compound layer due to humidification or heating lowers the solderability. 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. Degree of 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 collimator diameter of the fluorescent X-ray film thickness meter is 0.1 mm.

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

According to a fifth aspect of the present invention, there is provided a method for manufacturing a reflow solder plated square wire according to the first aspect of the present invention. That is, Sn-P
A method for producing a reflow solder-plated square wire in which a copper or copper alloy square wire having an electroplated b-alloy solder layer is run at a predetermined speed in a furnace heated to a predetermined temperature to perform a reflow process.
The running 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 in that the speed is set to.

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

[0012]

According to the reflow solder plating square wire of the present invention, since the crystal structure of the solder plating layer is composed of a polycrystalline Sn in which Pb is precipitated at the grain boundaries, the bonding between the crystal grains is strengthened and the bending process is performed. The generation of cracks and the generation of wear powder due to contact with the jig are prevented. Since Pb that does not react with Cu is precipitated at the grain boundary serving as a Cu diffusion path, the diffusion of Cu is suppressed and the copper-tin compound layer is formed thin. As a result, the bendability is improved and the deterioration of the solderability at high temperatures or the like is prevented. This effect is more remarkable as the average grain size of the solder plating layer becomes 2 μm or more and the grain boundary area becomes smaller. The above-mentioned copper-tin compound layer is a source of cracks due to its hardness. Its thickness is 0.45
By setting the thickness to not more than μm, the bendability is greatly improved.
By setting the traveling speed of the solder plating square wire in the reflow process 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 boundary of the Sn polycrystal is obtained, Bendability and solderability are improved. In addition, the thickness deviation of the corners of the square wire becomes 1.5 or less, and discoloration under humidification and heating is prevented.

[0013]

EXAMPLE A 0.5 mm square brass wire was electroplated with 9/1 solder, and this was subjected to a reflow treatment to produce a reflow solder plated square wire. FIG. 2 schematically shows the apparatus used. In the figure, 4
Is a brass square wire, 9 is a solder plating tank 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 is
The plating pretreatment is performed by passing through the electrolytic degreasing tank 5, the washing tank 6, the pickling tank 7, and the washing tank 16 in this order.
u was base-plated to a thickness of 1.0 μm, washed with water in a washing tank 26, and then electroplated with solder to a thickness of 2.0 μm in a solder plating tank 9. Next, this is washed in a washing tank 36, and a hot air drier 10
After drying, the reflow process is performed in the running furnace 11 and the cooling water tank
After cooling at 12, it was wound around a coiler 13. Solder plating was performed using a borofluoric acid-based electrolyte to which a smoothing agent was added. Reflow processing conditions were variously changed.

With respect to each of the thus obtained reflow solder plated square wires, corrosion resistance, solderability, bending properties, and abrasion resistance were examined. The corrosion resistance was determined by performing an accelerated deterioration test under the following conditions and determining whether or not the test material was discolored. The solderability was examined under the following conditions using the sample after the accelerated deterioration test. The bendability was determined by observing a surface crack after self-diameter winding with a stereoscopic microscope at a magnification of 1000 times, and determining the state of the crack. The abrasion resistance was determined by using a Bowden-type abrasion tester to check the generation of solder powder. A reflow tin-plated strip pressed at the tip 5R was used as a sliding probe, and the probe was reciprocated 100 times 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 thickness of the solder plating layer, and the thickness of the copper-tin compound layer. Accelerated deterioration test: humidity resistance test, temperature 105 ° C, relative humidity 100%
RH, leaving time 24 hours. Atmospheric heating test, temperature 155 ° C, leaving time 24 hours. Solderability test (meniscograf method): using eutectic solder, temperature 230
℃, flux 25% rosin / methanol, immersion speed 2mm
/ sec, immersion depth 2mm, immersion time 10sec, evaluation zero cross time.

[0015]

[Table 1]

[0016]

[Table 2]

As is clear from Tables 1 and 2, the products of the present invention (Nos. 1 to 8) exhibited good properties in all of the corrosion resistance, solderability, bending property and abrasion resistance. . No. 7 of these is
Since the crystal grain size of Sn was slightly reduced to 1.6 μm, the crystal grain boundaries increased, and the solderability and abrasion resistance were slightly reduced. or
In No. 8, since the thickness unevenness was slightly large at 1.6, Cu of the brass square wire partially diffused on the surface of the corner where the solder layer was thinned, causing slight discoloration. Also, the thickness of the compound layer becomes slightly thicker,
Workability deteriorated and bendability and abrasion resistance were somewhat reduced.

On the other hand, in Nos. 9 to 12 of the comparative examples, any one of the corrosion resistance, solderability, bending property and abrasion resistance was reduced. In the appearance after the moisture resistance test, the No. 11 and No. 12 samples showed yellow discoloration. This is because the crystal grains are small in diameter (Nos. 11 and 12), and especially in No. 12, the discoloration was large due to the addition of the additives. Regarding the solderability after the moisture resistance test, there was no significant difference in the wetting time (zero cross time) of about 1 second in all of Nos. 9 to 12. Even in the discolored Nos. 11 and 12, the oxide of Sn generated on the surface was easily dissolved in the molten solder in a short time, so that no decrease in solderability was observed.

Regarding the surface appearance after heating in the atmosphere, in the case of Nos. 9 and 10, the solder at the corners flowed to the flat portion and the solder thickness at the corners was reduced (large thickness deviation). Reacts with the square Cu diffused by heating to produce a copper-tin compound,
This was exposed and the corners turned gray. In Nos. 11 and 12, since the crystal grain size of the solder is dense and the space between the crystal grains is wide, Cu in 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 in air
In all of Nos. 9 to 12, the copper-tin compound was exposed on the surface, so that the wetting time was greatly increased.

In the self-diameter winding test (bendability), No. 9, 10
Nos. 11 and 12 had cracks because the copper-tin compound layer was thick, and Nos. 11 and 12 had unmelted solder layers and weak adhesion between crystal grains.

In the abrasion test, generation of solder powder was observed in all of Nos. 9 to 12. Although the cause of the generation of the solder powder in Nos. 9 and 10 is unknown, it is considered that the hard intermetallic compound layer was thick and tough, and the solder plating layer was easily scraped. In Nos. 11 and 12, the weakening of the bonding strength between the crystal grains was caused.

[0022]

As described above, the reflow solder-plated square wire of the present invention has improved corrosion resistance, solderability, bendability, and abrasion resistance, and the solder-plated copper square wire is subjected to reflow treatment under predetermined conditions. By doing so, it is industrially significant.

[Brief description of the 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 front page (56) References JP-A-7-157893 (JP, A) JP-A-3-191089 (JP, A) JP-A-2-270987 (JP, A)

Claims (5)

(57) [Claims] In a reflow solder plating square wire obtained by subjecting a Sn or Pb alloy solder layer to electroplating copper or a copper alloy square wire to a predetermined reflow treatment, the Sn—Pb alloy solder layer has Pb at a grain boundary. A reflow solder-plated square wire comprising a deposited polycrystalline Sn. 2. The reflow solder plating square wire according to claim 1, wherein the average value of the Sn crystal grain size of the solder plating 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. Plating square wire. 4. The reflow solder plating square wire according to claim 1, wherein the thickness k of the solder plating layer is 1.5 or less. Here, k = (maximum thickness of the solder plating layer measured by the fluorescent X-ray film thickness meter) / (average thickness of the solder plating layer measured by the constant current anodic melting method). However, the collimator diameter of the fluorescent X-ray film thickness meter shall be 0.1 mm. 5. A method for producing a reflow solder plated square wire in which a copper or copper alloy square wire electroplated with a Sn—Pb alloy solder layer is reflow-treated by running at a predetermined speed in a furnace heated to a predetermined temperature. 2. The reflow method according to claim 1, wherein a traveling speed of the copper or copper alloy square wire plated with the solder layer in the furnace is set to a speed of 80 to 96% of a lower limit speed at which the solder layer is in an unmelted state. Manufacturing method of solder plated square wire.