JP5065978B2 - Pb-less soldering method and soldered product - Google Patents

Description

  The present invention relates to a soldering method of Pb-less solder and a soldered product thereof, and more particularly, to a method of soldering Pb-less solder to a pattern made of Cu or Cu alloy plated with Ni and a soldered product thereof.

An example of a conventional soldered product of Pb-less solder will be described.
A conductor circuit composed of a Cu or Cu alloy pattern is provided on a substrate such as a multilayer printed wiring board, a Ni plating layer is provided on the conductor circuit, and solder bumps are connected via the alloy layer on the Ni plating layer. Yes. As solder constituting this solder bump, Pb-less solder of Cu 1 wt%, Ag 2 wt%, and Sn 97 wt% is used.

Next, a soldering method for the Pb-less solder will be described.
An Ni plating layer, a Pd layer, and an Au layer are sequentially formed on a conductor circuit of a substrate such as a multilayer printed wiring board. As a result, a solder pad composed of these three composite layers is formed. Next, solder is applied onto the solder pad and reflowed to form solder bumps on the solder pad. During this reflow, the Pd layer and the Au layer are diffused away to the solder bump side, and an alloy layer of the Ni plating layer and the solder composition metal is formed at the interface between the Ni plating layer and the solder bump (for example, Patent Document 1).

JP 2006-114705 A (paragraphs 43 to 51 and FIG. 6)

  By the way, in the conventional soldering method of Pb-less solder, the Ni plating layer serves as a barrier layer by providing a Ni plating layer between a conductor circuit made of a Cu or Cu alloy pattern and a solder bump. As a result, the solder bumps and the metal of the conductor circuit are prevented from diffusing each other.

However, Pb-less solder needs to have a higher soldering temperature than Pb-containing solder. For this reason, a part of the Ni plating layer diffuses into the Pb-less solder and disappears depending on the heat treatment conditions such as a relatively thin Ni plating layer or a long heating time during soldering. The Ni plating layer may partially fail to function as a barrier layer. As a result, the bonding strength between the Pb-less solder and the Cu or Cu alloy pattern is lowered, and the reliability of soldering with the Pb-less solder is lowered. Therefore, it is necessary to form a thick Ni plating layer as compared with the Pb-containing solder, and the plating cost increases.
The Ni plating layer generates a plating stress on the Cu or Cu alloy pattern and the substrate. This plating stress increases as the Ni plating thickness increases, which may reduce the reliability of the substrate. The plating stress is remarkable when the Ni plating is an alloy plating such as electroless Ni-P plating. Further, when the substrate is a ceramic substrate, the ceramic substrate may be broken in, for example, an assembly process of an electronic component because the plating stress is large.

  The present invention has been made in view of the above circumstances, and its purpose is to improve the bonding strength between a Pb-less solder and a pattern made of Cu or Cu alloy even if the Ni plating layer is thin. An object is to provide a soldering method of Pb-less solder and a soldered product thereof.

In order to solve the above-described problem, a soldering method for Pb-less solder according to the present invention includes a step of forming a Ni plating layer on a pattern made of Cu or Cu alloy,
Placing a Pb-less solder containing Sn as a main component on the pattern via the Ni plating layer, and performing a soldering process;
Comprising
In the soldering process, at least a part of the Ni plating layer is lost and the Pb-less solder is joined to the pattern.

  According to the soldering method of the Pb-less solder according to the present invention, at least a part of the Ni plating layer is eliminated by increasing the heating amount at the time of soldering with respect to the thickness of the Ni plating layer. And the bonding strength between the Pb-less solder can be increased.

  Moreover, in the soldering method of the Pb-less solder according to the present invention, Cu in the pattern, Ni in the Ni plating layer, and Sn in the Pb-less solder are joined to the joint where the Pb-less solder is joined to the pattern. It is preferable to further comprise a Cu—Ni—Sn phase or a Cu—Ni—Sn compound produced by mutual diffusion. Thereby, the joint strength between the pattern and the Pb-less solder can be increased.

  In the soldering method of Pb-less solder according to the present invention, Cu in the pattern can be diffused into the Pb-less solder by the soldering process. Thereby, the joint strength between the pattern and the Pb-less solder can be increased.

Moreover, in the soldering method of the Pb-less solder according to the present invention, the joint surface after the Pb-less solder is joined to the pattern may have undulations, and the undulation width may be 3 μm or more.
In the soldering method for Pb-less solder according to the present invention, the Ni plating layer may be an electroless Ni alloy plating layer or an electrolytic Ni plating layer.

A soldered product of Pb-less solder according to the present invention includes a pattern made of Cu or a Cu alloy,
Pb-less solder mainly composed of Sn bonded to the pattern;
A Cu—Ni—Sn phase or Cu—Ni—Sn compound formed at the joint between the pattern and the Pb-less solder;
It is characterized by comprising.

  Moreover, in the soldered product of the Pb-less solder according to the present invention, it is possible to have a Cu—Sn phase or a Cu—Sn compound in the joint portion.

  In the soldered product of Pb-less solder according to the present invention, the joint surface obtained by joining the Pb-less solder to the pattern may have a undulation, and the width of the undulation may be 3 μm or more.

  As described above, according to the present invention, the soldering method of Pb-less solder that can improve the bonding strength between the Pb-less solder and the pattern made of Cu or Cu alloy even if the Ni plating layer is thin, and The soldered product can be provided.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a schematic cross-sectional view for explaining a soldering method of Pb-less solder according to an embodiment of the present invention.

  FIG. 1 shows an example of the structure of a soldered product of Pb-less solder according to the present invention. Therefore, the soldered product of the Pb-less solder of the present invention is not limited to the one shown in FIG. 1, and includes all products or parts that solder Pb-less solder to a pattern made of Ni-plated Cu or Cu alloy. There is no particular limitation on the connection connected to the pattern by the Pb-less solder, and various types can be used. The said pattern is the meaning containing the pattern or member which consists of Cu or Cu alloy. Examples of the soldered product include a product in which a circuit pattern made of Cu or a Cu alloy is formed on a ceramic substrate, and a Ni plating layer is formed on the circuit pattern. Examples of the connection object include an electronic component.

  In this embodiment, a plurality of samples as shown in FIG. 1 are prepared, and the bonding strength between the Pb-less solder and the Cu pattern is measured by a peel test using these samples, and the Pb-less solder included in the present invention is determined based on the result. The specific range of soldering methods and soldered products will be clarified.

  First, a target product to which Pb-less solder was attached was prepared. As shown in FIG. 1, this target product has a Cu pattern 2 formed on the front and back surfaces of a substrate 1, a Ni plating layer 3 formed on the surface of the Cu pattern 2, and Ni plating on the center of the Cu pattern 2. A solder resist 4 having an opening through the layer 3 is provided. In the present embodiment, electroless Ni—P plating is formed as a Ni plating layer. Moreover, the pure Ni board 6 joined to this object by Pb-less solder was prepared. This pure Ni plate 6 is obtained by cutting a rolled Ni plate having a thickness of 0.2 mm into 20 mm × 7 mm and bending the tip side 7 mm in the longitudinal direction into an L shape. The substrate 1 is, for example, a ceramic substrate, and the material of the ceramic is preferably composed mainly of alumina, Al nitride, or silicon nitride. The Ni plating layer 3 is preferably electroless Ni—P plating, electroless Ni—B plating, or electrolytic Ni plating. The solder resist is not necessarily required because it prevents the solder from spreading unnecessarily. The solder resist is, for example, ink, and is formed by printing at a predetermined position of the Cu pattern 2 and a predetermined shape by screen printing or the like, and then curing by ultraviolet rays or heat. The object to be joined is a pure Ni plate 6 and is shown in the schematic diagram (FIG. 1), but may be a surface mounted by normal soldering such as a Cu plate, a semiconductor or a diode.

Next, the solder resist 4 uses a metal mask having an opening 5 mm × 5 mm and a thickness of 0.6 mm, and paste-like Pb-less solder 5 is applied by screen printing, and a pure Ni plate is applied on the applied Pb-less solder 5. 6 was installed. At this time, the contact area between the Pb-less solder 5 and the pure Ni plate 6 was about 7 × 7 mm ^2, and the thickness of the Pb-less solder was about 350 μm. A plurality of samples in which the thickness of the Ni plating layer 3 was changed to 1 μm, 2 μm, 3 μm, 4 μm, and 5 μm in such a configuration were prepared. In this embodiment, a 96.5 wt% Sn-3 wt% Ag-0.5 wt% Cu alloy is used as the Pb-less solder 5, but other alloys can be used as long as the Pb-less solder mainly contains Sn. It is also possible to use it. As other Pb-less solder compositions, for example, those having Sn of 90 wt% or more, such as 99.3 Sn-0.7 Cu and 96.5 Sn-3.5 Ag, are preferable. In addition, although there exist a paste, foil, plating, and a linear thing as a form, it is not specifically limited.

  Thereafter, the plurality of samples were put into a soldering furnace, and soldering treatment was performed at a temperature of 275 ° C. for 3 minutes, 6 minutes, and 8 minutes, and the holding time was changed. The soldering furnace atmosphere at this time is 80% nitrogen and 20% hydrogen.

  Next, the sample after soldering was heat-treated. Specifically, the sample after soldering was put into an oven heated to 125 ° C. and 150 ° C., and held for 0 hour (no heat treatment), 50 hours, 100 hours, 200 hours, 300 hours, and then air-cooled. The purpose of this heat treatment is to confirm a change with time in solderability (adhesion strength, etc.) due to temperatures of 125 ° C. and 150 ° C.

  Thereafter, the cross section of the soldered surface of this sample was observed with a laser microscope, and the thickness of the Ni plating layer was measured. The results are shown in FIGS.

FIG. 2 is a diagram showing the relationship between the thickness of the Ni plating layer (plating thickness) and the soldering time. As a sample for measuring this, a sample that was not subjected to heat treatment for confirming a change with time was used.
FIG. 3 is a diagram showing the relationship between the thickness of the Ni plating layer (plating thickness) and the heat treatment time for confirming the change with time. As a sample for measuring this, a sample having a heat treatment temperature of 125 ° C. for confirming a change with time was used.
FIG. 4 is a diagram showing the relationship between the thickness of the Ni plating layer (plating thickness) and the heat treatment time for confirming the change with time. A sample having a heat treatment temperature of 150 ° C. for confirming a change with time was used as a sample for measuring this. The Ni plating layer in FIGS. 2 to 4 is the thickness of the remaining Ni plating layer that has decreased due to mutual diffusion with Pb-less solder or the like after the Ni plating of a predetermined thickness is applied. Ni and other elements May be an alloy.

  According to FIG. 2, it was confirmed that the longer the soldering time, the thinner the plating thickness. This is considered that Ni of the Ni plating layer is diffused into the Pb-less solder. From the EDS analysis result described later, it was confirmed that a large amount of Ni diffused into the Pb-less solder.

According to FIGS. 3 and 4, it was confirmed that the plating thickness tends to be slightly thinner as the heat treatment time is longer. However, no significant reduction in plating thickness has been observed.
The tendency was to reduce the thickness of the Ni plating layer, but the reduction amount was very small. During the heat treatment (125 ° C., 150 ° C.), it is considered that Ni does not significantly diffuse.

2 to 4, it was confirmed that the decrease of the Ni plating layer was extremely quick during soldering as compared with that during heat treatment.
During soldering, the temperature of the solder is high, and since it is melted, the diffusion of Ni is considered to proceed extremely rapidly. In order to suppress the diffusion of Ni, it is considered necessary to shorten the soldering time.

Then, the shape observation of the cross section of the soldering surface of this sample and the element mapping analysis of the cross section were performed by SEM-EDS (scanning electron microscope and energy dispersive X-ray spectrometer attached thereto). As a result, a sample with a Ni plating layer thickness of 1 μm and a soldering time of 275 ° C. of 6 minutes and 8 minutes, and a Ni plating layer thickness of 2 μm and a soldering processing time of 8 minutes The following (1) to (4) were confirmed for all the samples.
(1) At least a part of the Ni plating layer on the soldering surface has disappeared. (2) Cu in the Cu pattern 2, Ni in the Ni plating layer 3, and Sn in the Pb-less solder 5 are mutually diffused. -Ni-Sn phase or Cu-Ni-Sn compound is formed in the joint (Pb-less solder side or joint surface) (3) Cu in Cu pattern 2 is diffused in Pb-less solder 5 (4) The joint surface after joining the Pb-less solder 5 to the Cu pattern 2 has waviness, and the width of this waviness is 3 μm or more. In addition, the wave | undulation before joining can hardly be confirmed by observation of the cross section by 4500 times with the laser microscope, and is less than 1 micrometer.
(5) Ni-Sn phase or Ni-Sn compound does not exist or is difficult to confirm

  FIG. 5 shows the results of cross-sectional observation and mapping analysis of the soldered surface of a sample that was not subjected to heat treatment for confirming the change with time when the thickness of the Ni plating layer was 1 μm and the heat treatment time during soldering was 8 minutes. FIG. As shown in FIG. 5, the above (1) to (5) were confirmed in this sample.

  FIG. 6 shows the results of the cross-sectional observation and mapping analysis of the soldered surface of the sample that was not subjected to the heat treatment for confirming the change over time when the thickness of the Ni plating layer was 5 μm and the heat treatment time for soldering was 8 minutes. FIG. As shown in FIG. 6, in this sample, it was confirmed that the Ni plating layer on the soldering surface was left about 3.0 μm, and a Ni—Sn layer was confirmed in the vicinity of the Ni plating layer 3. The above (1) to (5) were not confirmed.

Thereafter, the peel strength of the sample after the heat treatment is measured. Specifically, the Cu pattern and the substrate are restrained by a tensile tester, and the load at which the Pb-less solder 5 is peeled from the Ni-plated Cu pattern 2 is measured by pulling one end of the pure Ni plate 6. Since the solder joint portion of the pure Ni plate 6 is approximately 90 ° with respect to the tensile portion, a 90 ° peel test is performed.
Next, the peeling position (peeling mode) of the sample after this measurement was observed.

  The test results (peel strength and peel position) are shown in Tables 1 and 2. Table 1 shows the test result of the sample whose heat treatment temperature for confirming the change with time is 125 ° C., and Table 2 shows the test result of the sample whose heat treatment temperature for checking the change with time is 150 ° C. Note that the peeling position shown in Tables 1 and 2 is indicated as “Ni plating” because the Ni plating layer 3 is peeled off by solder on the entire peeling surface on the terminal side, and the sample (substrate side) This means the case where the Ni plating is peeled off and the Cu pattern is exposed, and the peeling position is indicated as “terminal” because the solder remains on the peeling surface of the sample (substrate side). This means that the peeling position is “terminal + plating” because the Ni plating layer 3 is left on a part of the peeling surface of the sample (substrate side), This means that the “Ni plating” and “terminal” modes in which the Cu pattern 2 is exposed are mixed.

As shown in Tables 1 and 2, the following was confirmed from the peel strength measurement results.
Samples in which the above (1) to (4) are confirmed, that is, samples having a Ni plating layer thickness of 1 μm and heat treatment times of 6 minutes and 8 minutes during soldering, and of the Ni plating layer A sample having a thickness of 2 μm and a heat treatment time of 8 minutes at the time of soldering had a relatively high peel strength and the peeling position tended to be “terminal”. A high peel strength means that the bonding strength between the Pb-less solder and the Cu pattern is high, and that the peeling position is “terminal” generally means that the soldering reliability by the Pb-less solder is high. To do. Further, when the thickness of the Ni plating layer is 1 μm and the soldering processing time is 8 minutes, the above (1) to (5) are confirmed and particularly preferable.

  The mechanism for improving the adhesion strength of the Pb-less solder of the present invention is presumed as follows.

  Table 3 summarizes the results of cross-sectional observation of the sample by SEM-EDS, measured values of the peel (peeling) strength of the terminal, and peeling mode.

The examples, comparative examples, and reference examples in Table 3 were extracted from the samples listed in Table 2, and the bonding cross section of the Cu pattern via Pb-less solder and Ni plating was observed.
In other words, a Ni terminal is placed on the surface of an electroless Ni—P plated layer of 1 to 5 μm on a Cu pattern at a temperature of 275 ° C. for a predetermined time via Pb-less solder (97 wt% Sn-2 wt% Ag-1 wt% Cu). In addition to soldering, the section of the sample when the heat treatment is performed for a predetermined time at a predetermined temperature is cut, element mapping is performed by SEM-EDS, and what phase or compound is formed, This is a summary of measurements of the size of the waviness at the joint interface. For reference, the peel strength and peel mode from the peel test are also listed.

From Table 3, Example 1 is a sample with a Ni plating thickness of 1 μm, a soldering treatment time of 275 ° C. for 8 minutes, and no heat treatment.
After soldering, no Ni plating layer remained, and the Cu phase of the Cu pattern near the original Ni plating layer and the Pb-less solder side interface (joint surface) had undulations of 3 μm or more. In addition, Sn phase, Cu-Ni-Sn phase or Cu-Ni-Sn compound, Cu-Sn phase or Cu-Sn compound could be confirmed on the Pb-less solder side. The adhesion strength according to the peel test was 101.9 N / cm, and the peeling mode was “terminal”.

Comparative Example 1 is a sample having a Ni plating thickness of 1 μm, a soldering treatment time of 275 ° C. for 3 minutes, a heat treatment temperature of 150 ° C. and a heat treatment time of 300 hours.
After soldering, the Ni plating layer remained slightly with a thickness of about 0.4 μm, and the interface between the Cu phase of the Cu pattern and the Ni plating layer (to be used as the bonding interface) had a swell of about 2 μm. . Further, Sn phase, Cu—Sn phase or Cu—Sn compound could be confirmed on the Pb-less solder side. Moreover, the Ni plating layer of the joint surface remained, and it turned out that it became a Ni-Sn layer according to EDS. The adhesion strength according to the peel test was 19.6 N / cm, and the peeling mode was “Ni plating”.

Example 2 is a sample having a Ni plating thickness of 1 μm, a soldering treatment time of 275 ° C. for 8 minutes, a heat treatment temperature of 150 ° C. and a heat treatment time of 300 hours.
After the soldering, no Ni plating layer remained, and the Cu phase of the Cu pattern in the vicinity of the original Ni plating layer and the interface on the Pb-less solder side (referred to as the bonding interface) had undulations of 5 μm or more. In addition, Sn phase, Cu-Ni-Sn phase or Cu-Ni-Sn compound, Cu-Sn phase or Cu-Sn compound could be confirmed on the Pb-less solder side. In addition, a Cu—Ni—Sn phase or Cu—Ni—Sn compound, a Cu—Ni phase or a Cu—Ni compound was confirmed in the vicinity of the original Ni plating layer (joint portion). The adhesion strength according to the peel test was 51.0 N / cm, and the peeling mode was “terminal + Ni plating”.

Comparative Example 2 is a sample having a Ni plating thickness of 3 μm, a soldering treatment time of 275 ° C. for 3 minutes, a heat treatment temperature of 150 ° C. and a heat treatment time of 300 hours.
After soldering, a Ni plating layer remained with a thickness of about 1.1 μm, and according to EDS, the layer was a Ni—Sn phase or a Ni—Sn compound. In addition, the interface between the Cu phase of the Cu pattern and the Ni plating layer (the bonding interface) did not swell.
Further, Sn phase, Cu—Ni—Sn phase or Cu—Ni—Sn compound, and Ni—Sn phase or Ni—Sn compound were confirmed on the Pb-less solder side.
The adhesion strength according to the peel test was 17.6 N / cm, and the peeling mode was “Ni plating”.

Reference Example 1 is a sample having a Ni plating thickness of 3 μm, a soldering treatment time of 275 ° C. for 8 minutes, a heat treatment temperature of 150 ° C. and a heat treatment time of 300 hours.
After soldering, the Ni plating layer remains with a thickness of about 0.9 μm, and according to EDS, the layer is a Ni—Sn phase or Ni—Sn compound and a Cu—Ni—Sn phase or Cu—Ni—Sn compound. It was made up of. Further, the interface between the Cu phase of the Cu pattern and the Ni plating layer (referred to as the bonding interface) had a wave of about 1.5 μm.
Further, Sn phase, Cu—Ni—Sn phase or Cu—Ni—Sn compound, and Ni—Sn phase or Ni—Sn compound were confirmed on the Pb-less solder side.
The adhesion strength according to the peel test was 100.0 N / cm, and the peeling mode was “terminal”.

Reference Example 2 is a sample having a Ni plating thickness of 4 μm, a soldering treatment time of 275 ° C. for 3 minutes, a heat treatment temperature of 150 ° C. and a heat treatment time of 300 hours.
After soldering, the Ni plating layer remained with a thickness of about 2.0 μm, and according to EDS, the layer consisted of a Ni—Sn phase or a Ni—Sn compound and a Ni phase. In addition, the interface between the Cu phase of the Cu pattern and the Ni plating layer (the bonding interface) did not swell.
Further, Sn phase, Ni—Sn phase or Ni—Sn compound could be confirmed on the Pb-less solder side.
The adhesion strength according to the peel test was 101.9 N / cm, and the peeling mode was “terminal”.

Reference Example 3 is a sample having a Ni plating thickness of 4 μm, a soldering treatment time of 275 ° C. for 8 minutes, a heat treatment temperature of 150 ° C. and a heat treatment time of 300 hours.
After soldering, the Ni plating layer remained with a thickness of about 1.5 μm, and according to EDS, the layer consisted of Ni—Sn phase or Ni—Sn compound and Ni phase. The interface between the Cu phase of the Cu pattern and the Ni plating layer (referred to as the bonding interface) had a undulation of about 1.0 μm.
Further, Sn phase, Cu—Ni—Sn phase or Cu—Ni—Sn compound was confirmed on the Pb-less solder side.
The adhesion strength according to the peel test was 64.7 N / cm, and the peeling mode was “Ni plating”.

Reference Example 4 is a sample having a Ni plating thickness of 5 μm, a soldering treatment time of 275 ° C. for 3 minutes, a heat treatment temperature of 150 ° C. and a heat treatment time of 300 hours.
After soldering, the Ni plating layer remained with a thickness of about 2.5 μm, and according to EDS, the layer consisted of a Ni—Sn phase or a Ni—Sn compound and a Ni phase. In addition, the interface between the Cu phase of the Cu pattern and the Ni plating layer (the bonding interface) did not swell.
In addition, Sn phase, Ni—Sn phase or Ni—Sn compound was confirmed on the Pb-less solder side.
The adhesion strength according to the peel test was 90.2 N / cm, and the peeling mode was “terminal”.

Reference Example 5 is a sample having a Ni plating thickness of 5 μm, a soldering treatment time of 275 ° C. for 8 minutes, a heat treatment temperature of 150 ° C. and a heat treatment time of 300 hours.
After soldering, the Ni plating layer remained with a thickness of about 2.0 μm, and according to EDS, the layer consisted of a Ni—Sn phase or a Ni—Sn compound and a Ni phase. The interface between the Cu phase of the Cu pattern and the Ni plating layer (referred to as the bonding interface) had a swell of about 0.5 μm.
In addition, Sn phase, Ni—Sn phase or Ni—Sn compound was confirmed on the Pb-less solder side.
The adhesion strength according to the peel test was 66.6 N / cm, and the peeling mode was “Ni plating”.

Reference Example 6 is a sample having a Ni plating thickness of 5 μm, a soldering treatment time of 275 ° C. for 8 minutes, and no heat treatment.
After soldering, the Ni plating layer remained with a thickness of about 2.3 μm. According to EDS, the layer was composed of a Ni—Sn phase or a Ni—Sn compound and a Ni phase. The interface between the Cu phase of the Cu pattern and the Ni plating layer (referred to as the bonding interface) had a undulation of about 1.0 μm.
In addition, Sn phase, Ni—Sn phase or Ni—Sn compound was confirmed on the Pb-less solder side.
The adhesion strength according to the peel test was 86.2 N / cm, and the peeling mode was “terminal”.

The above is the cross-sectional analysis result by SEM-EDS of the Example of Table 3, a comparative example, and a reference example.
Note that P is always present at the location where Ni is present, and the location where Ni is present coincides with the location where P is present.

  Further, for Comparative Example 1 in Table 3, elemental analysis was similarly performed by SEM-EDS on the joint interface (fracture surface) of the Ni terminal after the peel strength test was completed, and Ni, Sn, and P were detected. (Not shown).

  As described above, the mechanism for deteriorating the adhesion of Ni plating is inferred from the observation of the bonding cross section and the fracture surface in Table 3 as follows.

First, a Ni—Sn phase or Ni—Sn compound is formed near the interface between the Ni plating and the Pb-less solder and in the Pb-less solder by a heat treatment such as a soldering process.
When the Ni—Sn phase or Ni—Sn compound is further heated, the diffusion of Ni and Sn proceeds to increase the amount thereof, and the original Ni plating layer becomes thinner. At this time, if the Ni phase becomes too thin, it is estimated that the adhesion strength rapidly decreases.
That is, it can be considered that the formation and presence of a Ni—Sn phase or a Ni—Sn compound is one major factor in the deterioration of adhesion strength. This is because the elements of Ni, Sn, and P are confirmed by observation of the fracture surface, and the Ni—Sn phase or Ni—Sn compound is confirmed near the original Ni plating layer in Comparative Example 1 and Comparative Example 2. It is supported by being.

  Therefore, as in Reference Examples 2 to 6, if the thickness of the original Ni plating layer is increased to some extent in advance, a Ni phase is present on the bonding surface, and a decrease in soldering adhesion strength can be prevented. This is a measure for preventing the deterioration of the adhesion strength of the conventional and current plating, and is effective.

  Further, in detail in Reference Examples 2 to 6, in Reference Examples 3 and 5 having a large amount of heat applied by the soldering process, the adhesion strength (peel strength) is good at 50 N / cm or more, but the peeling mode. Is “Ni plating”. This is predicted that if heat treatment (amount of heat) is further applied, the Ni-Sn phase or Ni-Sn compound will make the Ni phase thinner and eventually cause deterioration in adhesion strength. It is considered that this peeling mode is changed from “terminal” to “Ni plating”.

  On the other hand, Examples 1 and 2 according to the present invention are completely different from the method of increasing the thickness of the Ni plating to prevent the Ni plating layer from being thinned by reaction, and leaving the Ni plating phase to remain. Different.

In the present invention, the Ni plating phase is rather thinned, at least a part of the Ni plating layer disappears, and the Ni—Sn phase or Ni—Sn compound is diffused into the Cu—Ni—Sn phase or Cu—Ni— by diffusion. By applying heat until Sn compounds are obtained.
That is, the Ni plating layer is not allowed to remain and act as a barrier layer as in the prior art, but the Ni plating layer disappears and a Ni—Sn phase or a Ni—Sn compound, which is considered to be a cause of a decrease in adhesion, is once generated. However, the reaction is continued until a Cu—Ni—Sn phase or Cu—Ni—Sn compound is obtained by further applying heat. This proved that the deterioration of the adhesion strength can be suppressed. The results of Examples 1 and 2 in Table 3 are thought to support this.

  The present invention has found that the above reaction proceeds by applying a heat quantity two to three times that of conventional soldering processing conditions, and that once the adhesion strength has been lowered, the adhesion strength once again has high adhesion strength. It was.

  In addition, as an indicator that the reaction is proceeding appropriately, it is preferable that a Cu—Sn phase or a Cu—Sn compound is further present, and the undulation of the bonding interface is 3 μm or more.

The waviness refers to the upper and lower widths when the interface between the Cu phase of the Cu pattern and another phase (Ni or Pb-less solder or the like) is undulated when the cross section of the bonded substrate is observed.
The roughness of the surface of the Cu pattern before bonding is 0.1 μm or less, and the Cu plate after bonding the Cu pattern to the substrate has a surface enlarged to the extent of 5,000 times the cross section by SEM (scanning electron microscope). Nothing was observed that could be measured as waviness.

  Without Ni plating, changes in Cu or Cu alloy pattern over time such as oxidation cannot be prevented, and furthermore, a high strength portion of the Cu—Ni—Sn phase or Cu—Ni—Sn compound cannot be formed. The lower limit of the Ni plating thickness to be applied is preferably 0.3 μm, more preferably 0.5 μm or more.

Further, considering the cost of Ni plating and the influence of Ni plating stress on the substrate, the upper limit is about 3 μm, and more preferably 2.5 μm.
That is, after Ni plating is performed in a range of 0.3 to 3 μm, preferably 0.5 to 2.5 μm, at least a part of the Ni plating layer is preferably lost by a heat treatment such as a soldering process.

  Note that, according to SEM-EDS, for example, it is difficult to distinguish between a Ni—Sn phase and a Ni—Sn compound, so that the Ni—Sn phase or Ni—Sn compound is used. There is no problem as a Ni-Sn compound.

  From the above test results, the Ni plating layer can be eliminated by increasing the amount of heating at the time of soldering relative to the thickness of the Ni plating layer, thereby joining the Cu pattern 2 and the Pb-less solder 5. It was confirmed that the strength could be increased and the reliability of soldering with Pb-less solder was improved. Further, it was confirmed that even when heat treatment for confirming the change with time at temperatures of 125 ° C. and 150 ° C. was performed, both the bonding strength between the Cu pattern 2 and the Pb-less solder 5 and the reliability of soldering did not decrease.

In addition, a Cu—Ni—Sn phase or Cu—Ni—Sn compound in which Cu in the Cu pattern 2, Ni in the Ni plating layer 3, and Sn in the Pb-less solder 5 diffuse each other is formed on the soldering surface. Thus, it was confirmed that the bonding strength between the Cu pattern 2 and the Pb-less solder 5 can be increased.
It was also confirmed that the bonding strength between the Cu pattern 2 and the Pb-less solder 5 can be increased by diffusing Cu in the Cu pattern 2 into the Pb-less solder 5.
Further, the bonding surface after bonding the Pb-less solder 5 to the Cu pattern 2 has waviness, and the width of the waviness is 3 μm or more, thereby increasing the bonding strength between the Cu pattern 2 and the Pb-less solder 5. I was able to confirm.

  Conventionally, by causing the Ni plating layer to function as a barrier, diffusion of Sn into the Cu pattern was prevented, thereby maintaining a high bonding strength between the solder and the Cu pattern. For this reason, when using Pb-less solder that increases the soldering temperature, it is necessary to form a thick Ni plating layer according to the soldering temperature and time. However, in this embodiment, since the bonding strength and reliability can be improved by eliminating the Ni plating layer, the Ni plating layer can be formed thin.

  The thickness of the Ni plating layer 3 depends on the amount of heating at the time of soldering, but if the heating temperature at the time of soldering is 275 ° C. for 6 minutes or more, it can be 1 μm or less, and the heating at the time of soldering If the temperature is 275 ° C. for 8 minutes or longer, it can be made 2 μm or less.

  In addition, this invention is not limited to the said embodiment and said Example, A various change can be implemented within the range which does not deviate from the main point of this invention.

It is typical sectional drawing for demonstrating the soldering method of the Pb-less solder by embodiment of this invention. It is a figure which shows the relationship between the thickness (plating thickness) of Ni plating layer, and soldering time. It is a figure which shows the relationship between the thickness (plating thickness) of Ni plating layer, and the heat processing time for time-dependent confirmation. It is a figure which shows the relationship between the thickness (plating thickness) of Ni plating layer, and the heat processing time for time-dependent confirmation. It is a figure which shows the result of the cross-sectional mapping analysis of the sample whose thickness of Ni plating layer is 1 micrometer. It is a figure which shows the result of the cross-sectional mapping analysis of the sample whose thickness of Ni plating layer is 5 micrometers.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Board | substrate 2 ... Cu pattern 3 ... Ni plating layer 4 ... Solder resist 5 ... Pb-less solder 6 ... Pure Ni board

Claims (9)

Forming a Ni plating layer on a pattern made of Cu or Cu alloy;
Placing a Pb-less solder containing Sn as a main component in contact with the Ni plating layer on the pattern, and performing a soldering process;
Comprising
A soldering method of Pb-less solder, wherein at least a part of the Ni plating layer is eliminated by the soldering process and the Pb-less solder is joined to the pattern.   In Claim 1, Cu- which produced | generated by the Cu in the said pattern, Ni in the said Ni plating layer, and Sn in the said Pb-less solder mutually diffuse | diffused in the junction part which joined the said Pb-less solder to the said pattern. A soldering method for Pb-less solder, further comprising a Ni—Sn phase or a Cu—Ni—Sn compound.   3. The soldering method for Pb-less solder according to claim 1, wherein Cu in the pattern diffuses into the Pb-less solder by the soldering process.   4. The Pb-less solder according to claim 1, wherein a bonding surface after the Pb-less solder is bonded to the pattern has a undulation, and the width of the undulation is 3 μm or more. 5. Soldering method. In any 1 item | term of the Claims 1 thru | or 4, The said Ni plating layer is an electroless Ni plating alloy layer which consists of electroless Ni-P plating or electroless Ni-B plating , or an electrolytic Ni plating layer, It is characterized by the above-mentioned. Pb-less soldering method. 6. The method of soldering Pb-less solder according to claim 1, wherein the Ni plating layer has a thickness of 0.5 to 2.5 [mu] m. A pattern made of Cu or Cu alloy;
Pb-less solder mainly composed of Sn bonded to the pattern;
A Cu—Ni—Sn phase or Cu—Ni—Sn compound formed at the joint between the pattern and the Pb-less solder;
Equipped with,
A soldered product of Pb-less solder, characterized in that Au is not contained in the joint portion . 8. The soldered product of Pb-less solder according to claim 7 , wherein the joint has a Cu—Sn phase or a Cu—Sn compound. According to claim 7 or 8, the bonding surface bonded to the Pb-less solder to said pattern has a waviness, Pb-less solder soldering article, wherein the width of said undulation is 3μm or more.