JPH11295206A - Solder wettability evaluation method - Google Patents

Abstract

(57) [Summary] [Problem] To clearly obtain a difference in wettability according to a material type of a solder paste and a material of a test piece. SOLUTION: A substrate 11 is formed by forming a circular copper land 13 on a base material 12 and surrounding the copper land 13 with a solder resist 14. A required amount of solder paste 21 is applied on the copper land 13 (solder leveler 16) of the substrate 11 by printing. A test piece 15 made of a copper plate is vertically arranged on the solder paste 21 so as to stand vertically. The whole is heated under a predetermined temperature condition through a reflow furnace to melt the solder 21. Test piece 1
The wettability of the solder 21 is evaluated based on the wetted area of the solder 21 with respect to No. 5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for evaluating the wettability of a solder so that the difference in the wettability is remarkable depending on the material type of the solder paste and the material of the test piece.

[0002]

For example, there are various methods for evaluating the wettability (solderability) of solder (solder paste) used for mounting electronic components on a printed wiring board, including those specified in JIS. At present, mainly the following wettability evaluation method is generally used.

That is, as shown in FIG. 7, a solder paste 2 is printed and applied on the upper surface of a copper plate 1 so as to form a circle, and a test piece 3 made of a copper pipe is vertically set in contact with the solder paste 2. To place. Then, the copper plate 1 is placed on a hot plate 4 and heated by a heater to melt the solder paste 2, and the wetting force (tensile force) of the solder 2 on the test piece 3 based on the meniscus principle is measured using a weight meter 5. Thereby, the wettability of the solder 2 is evaluated.

FIG. 8 (a) shows how the temperature changes over time (temperature profile) when the solder paste 2 is heated by the above-described method. For example, the temperature changes from room temperature to 2 deg / sec. Raise the temperature to 150 ° C.
After maintaining the temperature at 50 ° C. for a certain time, the temperature is further increased to about 200 ° C. FIG. 8B shows how the wetting force changes after the melting point of the solder, and the maximum wetting force appears when the solder is wetted on the test piece 3.

However, in the evaluation method based on the measurement of the wetting force as described above, even if the kind of the solder paste is changed or the material of the test piece is changed, a remarkable difference is observed in the evaluation result. Therefore, there was a problem that the quality of the wettability could not be evaluated sufficiently clearly.

FIG. 9 shows the results of evaluation of the wetting force of the present inventors for three different types of solder pastes 2 (materials A, B, and C). It cannot be done. Also, no remarkable difference was observed in the wet state of the solder 2 with respect to the test piece 3. Furthermore, in the actual component mounting process, the solder is melted and hardened by passing it through a reflow oven, but the solder wettability evaluated by the above method and the solder wettability when an actual reflow oven is used And sometimes did not correspond.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a solder wettability evaluation method capable of clearly obtaining a wettability difference according to the material type of a solder paste and the material of a test piece. To provide.

[0008]

Means for Solving the Problems The present inventor has conducted a conventional method of evaluating wettability, that is, applying a solder paste to a copper plate, heating the copper plate on a hot plate, and applying wetness to the test piece. In the evaluation method for obtaining power,
It is estimated that there are two factors that make clear evaluation impossible. That is, the first factor is that the solder paste is applied on the copper plate, so that the molten solder spreads freely in the horizontal direction, and the amount of solder that wets the test piece varies, The second factor is that, since the heating is performed from the lower surface of the copper plate, the test pieces are heated with a delay from the heating of the copper plate, causing a shift or a temperature difference between the heating points. Then, the inventor confirmed that the estimation was valid, and accomplished the present invention.

That is, the method for evaluating the wettability of a solder according to the present invention comprises the steps of:
A required amount of solder paste is applied in a state where the spread in the horizontal direction is regulated, and in a state where the test piece is set on the solder paste, the whole is heated to melt the solder paste,
The method is characterized in that the wettability is evaluated based on the wetting state of the solder on the test piece.
Invention).

According to this, since the solder paste is applied to the application area of the substrate in a state where the spread in the horizontal direction is regulated, the molten solder does not spread on the substrate, and the solder paste which wets the test piece is prevented. Fluctuations in volume can be prevented. Further, since the whole is heated when the solder is melted, the substrate and the test piece are heated in the same manner.
As a result, in evaluating the wettability based on the wet-up state of the solder on the test piece, it became possible to clearly obtain a difference in wettability according to the material type of the solder paste and the material of the test piece. It is.

At this time, the spread of the solder on the substrate in the horizontal direction can be regulated by applying a solder resist around the application area of the substrate (the invention of claim 2). The spread of the solder on the substrate in the horizontal direction can be reliably regulated by a simple method.

The solder paste may be melted by passing the substrate through a reflow furnace (the invention of claim 3), whereby the whole can be heated under uniform conditions. In addition, the wettability of the solder can be evaluated under the conditions actually used.

Further, if the test piece is formed in such a shape that the portion where the solder comes into contact with the solder paste and the solder wets up stably (invention of claim 4), the test piece is arranged vertically. Since there is no need for a separate means for
Be more effective. At this time, various shapes such as a U-shape, an inverted V-shape, a cylindrical shape, and an L-shape on the upper surface can be considered as a shape in which the test piece stands stably vertically.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention (corresponding to claims 1 to 3) will be described below with reference to FIGS. First, in this example, equipment and devices used for performing the method for evaluating solder wettability will be described.

As shown in FIG. 1, a substrate 11 used for evaluation is formed on a base material 12 made of, for example, glass epoxy.
A copper land 13 is provided as an application area, and a solder resist 14 for controlling the spread of solder, which will be described later, is provided around the copper land 13 and is configured. On the other hand, the test piece 15 is formed of a rectangular thin copper plate as shown in FIG.

At this time, the copper land 13 is formed, for example, in a circular shape having a diameter of 6 mmφ, and a solder leveler 16 is provided on its upper surface as shown in FIG. The test piece 15 has a length and width of, for example, 5 mm × 9 mm and a thickness of, for example, 0.3 mm, and is further subjected to, for example, forced oxidation at 240 ° C. for 30 minutes.

On the other hand, a reflow furnace 17 used for heating
Is composed of, for example, an air reflow furnace combined with IR of a whole heating system, and as shown schematically in FIG.
A transport path 18 for transporting the substrate 11 in the direction of arrow a is provided from 7a to the outlet 17b. A plurality of heaters 19 including infrared heaters It is arranged. Thus, a preheat zone, a reflow zone, and a cooling zone are formed in this order from the entrance 17a side. Further, a cooling fan device 20 is provided in the cooling zone on the outlet 17b side.

The procedure for evaluating the wettability of the solder will now be described with reference to FIGS. In performing the evaluation, first, as shown in FIGS. 1 and 2A, a required amount of solder paste 21 is applied on the copper land 13 (solder leveler 16) of the substrate 11. The application of the solder paste 21 is performed by, for example, printing using a metal mask (not shown). In this case, for example, a thickness of 0.
A circular opening having a diameter of 6 mm is formed in a metal mask equivalent to 3 mm, and the solder paste 21 is formed into a circular shape having a diameter of 6 mm and a thickness of 0.3 mm by being printed and applied through the opening. It will be applied to.

Next, as shown in FIG. 1 and FIG.
On the solder paste 21 applied on the substrate 11,
The test piece 15 is arranged vertically in a vertically long state. At this time, the test piece 15 is held in an upright state using a clip (not shown) or the like.

Then, the substrate 11 on which the test pieces 15 are placed as described above is passed through the reflow furnace 17 and
1. The entire test piece 15 and the solder paste 21 are heated. As the substrate 11 is sequentially fed on the transport path 18, the whole is gradually heated by the heater 19 and the solder paste 21 is melted.
As shown in (b), the solder 21 becomes wet with respect to the test piece 15 due to the surface tension.

At this time, the better the wettability between the solder 21 and the test piece 15 is, the larger the wet-up amount of the solder 21 is. However, the solder paste 21 is applied to the solder resist 14 in the horizontal direction on the substrate 11. Since the spread of the solder 21 is restricted, the molten solder 21 does not spread on the substrate 11, and the amount of the solder 21 corresponding to the wettability always wets the test piece 15. Also, at this time, since the entire heating is performed by the reflow furnace 17, the substrate 11, the solder paste 21, and the test piece 15 are similarly heated, and uneven heating between the substrate 11 and the test piece 15 causes a large unevenness. No temperature difference occurs.

Here, the temperature condition for heating the solder paste 21 in the reflow furnace 17 is set to 2 as shown in the temperature profile (temperature-time curve) shown in FIG.
We carry out by kind. In the temperature condition L, the preheat temperature is 140 ° C. and the peak temperature is 200 ° C., and in the temperature condition H, the preheat temperature is 160 ° C. and the peak temperature is 230 ° C.

Thereafter, the substrate 11 is discharged from the reflow furnace 17 while the solder 21 is cooled and hardened and the test piece 15 is soldered.
The wettability of the solder 21 is evaluated based on the wet-up state of No. 1. In this case, in the present embodiment, the wettability is evaluated by calculating the area (shown with hatching for convenience) of the wetted portion of the solder 21 of the test piece 15 as shown in FIG. It is performed by

FIG. 5 shows the results of the evaluation of the wetting force (the wet-up area) of three different solder pastes 21 (materials A, B, and C) using the above-described evaluation method. Each material is evaluated using the above two types of temperature conditions (L, H). As is clear from FIG. 5, when the evaluation method of this embodiment is used,
Unlike the conventional evaluation method (see FIG. 9), the wettability (the wet-up area) between the materials A, B, and C of the solder 21
There was a clear difference between the two. Also, even with the same material, a difference in wettability depending on the temperature condition was clearly obtained.

In the conventional method for evaluating wettability, the molten solder 2 spreads freely on the copper plate 1 in the horizontal direction, and the amount of solder that wets the test piece 3 varies, and heating is performed on the copper plate. 1 is performed only from the lower surface of the test piece 1, there is a difference in the heating time between the copper plate 1 and the test piece 3 and a temperature difference. On the other hand, in the evaluation method of this embodiment, the solder 21 is Since the upper portion is melted in a state where the spread in the horizontal direction is restricted, the solder 21 in an amount corresponding to the wettability always comes up to the test piece 15, and the whole heating by passing through the reflow furnace 17 causes It is considered that this is because the substrate 11 and the test piece 15 are uniformly heated.

Although detailed description is omitted, according to the above-described method for evaluating wettability, the solder 2 made of the same material is used.
It has also been confirmed that even with 1, the difference in wettability due to the difference in the material of the test piece 15 (for example, the difference between copper and nickel) can be remarkably obtained.

As described above, according to the evaluation method of this embodiment,
The solder paste 21 is applied to the substrate 11 in a state in which the solder paste 21 does not spread in the horizontal direction, the test piece 15 is placed on the solder paste 21, and the whole is heated. Since the wettability of the solder 21 was evaluated, the solder paste 21 was used.
This has an excellent effect that a difference in wettability according to the material type and the material of the test piece 15 can be clearly obtained.

Further, in this embodiment, particularly, the spread of the solder 21 on the substrate 11 in the horizontal direction is controlled by applying the solder resist 14, so that the solder 21 on the substrate 11 can be surely formed by a simple method. 21 can be restricted from spreading in the horizontal direction. Further, since the melting of the solder paste 21 is performed by passing through the inside of the reflow furnace 17, there is a merit that the wettability of the solder 21 can be easily evaluated under the actually used conditions. What you can get.

FIG. 6 shows test pieces 31 to 34 according to another embodiment (corresponding to claim 4) of the present invention. These can be called modified examples of the test piece having a changed shape in place of the rectangular plate-shaped test piece 15 in the above embodiment.
The shape is such that the part that gets wet is stably standing vertically by itself.

That is, the test piece 31 shown in FIG. 6A is formed in a U-shape with the open part facing downward.
The test piece 32 shown in (b) is formed in an inverted V shape, the test piece 33 shown in FIG. 6 (c) has a cylindrical shape, and the test piece 34 shown in FIG. , L seen from the top
It is formed in the shape of a letter. According to these, in addition to the operation and effect similar to those of the above-described embodiment, it is possible to obtain an effect that an additional means for vertically disposing the test pieces 31 to 34 becomes unnecessary.

In the above embodiment, the reflow furnace 17 is used for overall heating, but the entire heating may be performed using, for example, a high-temperature bath. Further, in the above-described embodiment, the wettability is evaluated by determining the wet-up area of the solder 21, but the wettability can be evaluated by determining the wet-up height. In addition, the present invention is not limited to each of the above-described embodiments. For example, the materials and specific dimensions of each of the above-described portions are merely examples, and the present invention may be implemented with appropriate changes without departing from the scope of the invention. What you get.

[Brief description of the drawings]

FIG. 1 shows an embodiment of the present invention, and is a longitudinal sectional front view of a substrate on which test pieces are arranged.

FIG. 2 is a perspective view showing states of a test piece before solder melting (a), after solder melting (b), and when measuring a wet area (c) in order.

FIG. 3 is a longitudinal side view schematically showing a configuration of a reflow furnace.

FIG. 4 is a diagram showing two types of temperature profiles when solder is melted in a reflow furnace.

FIG. 5 is a diagram showing evaluation results for three types of solders.

FIG. 6 shows another embodiment of the present invention, and is a perspective view showing the shapes of four different test pieces.

FIG. 7 shows a conventional example, and is a perspective view schematically showing a state at the time of evaluation.

FIG. 8 is a diagram showing a change in temperature (a) and a change in wetting force (b) over time.

FIG. 9 is a diagram showing evaluation results for three types of solders.

[Explanation of symbols]

In the drawing, 11 is a substrate, 13 is a copper land (application area), 1
4 is a solder resist, 15, 31, 32, 33, and 34 are test pieces, 17 is a reflow furnace, and 21 is solder (solder paste).

Claims (4)

[Claims] 1. A state in which a required amount of solder paste is applied to an application area provided on a horizontally arranged substrate in a state where the spread in a horizontal direction is regulated, and a test piece is placed on the solder paste. Then, the solder paste is melted by heating the whole, and the wettability is evaluated based on the wet-up state of the solder on the test piece. 2. The evaluation of solder wettability according to claim 1, wherein the regulation of the spread of the solder on the substrate in the horizontal direction is performed by applying a solder resist around the application area. Method. 3. The method according to claim 1, wherein the melting of the solder paste is performed by passing the substrate through a reflow furnace. 4. The test piece according to claim 1, wherein the test piece has a shape in which a portion where the solder is wetted in contact with the solder paste stands vertically and stably. The solder wettability evaluation method described.