JP3759686B2 - Chip soldering method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a chip mounting method, and more particularly to a soldering method used for connecting a small chip of a light emitting element to a wiring pattern on a substrate.
[0002]
[Prior art]
The chip mounting method can be broadly divided into a wire bonding method in which the electrodes on the chip and conductors on the lead frame and the stem are connected by wires, and wireless in which the chip is directly connected to the wiring pattern on the substrate without using wires. There is a bonding method.
[0003]
The wire bonding method requires a thickness of 100 μm or more on the chip for wire arrangement, and thus there is a limit to thinning the device. In addition, since the wire bonding method requires an area for the wire to extend around the chip, the distance between the chips cannot be made smaller than 2 mm, and there is a limit to the miniaturization (area) of the device.
[0004]
On the other hand, the wireless bonding method solves such drawbacks of the wire bonding method, and is an advantageous chip mounting method for realizing miniaturization and thinning of the device. One of the wireless bonding methods is a soldering method. However, when the soldering method is applied to a small chip, since the small chip has a small area to be soldered, a special method must be used for soldering. As one of them, a method having the following steps is known.
[0005]
(1) Apply cream-like solder to the chip component mounting location on the board.
(2) Place the chip component on the solder. At this time, this part is not fixed.
(3) The substrate on which the chip parts are mounted is put into a reflow furnace. Solder melts and solidifies in the furnace, and the soldering of the chip parts is completed.
This method is a so-called reflow soldering method.
[0006]
[Problems to be solved by the invention]
The above-described conventional soldering method is an effective method for a small part having a certain weight, such as a chip resistor. This is because the chip sinks into the solder due to the weight, and the electrode of the chip and the wiring pattern of the substrate are well soldered. However, in the case of a light-weight chip, for example, a light-emitting element, the chip does not sink into the solder, and the chip, that is, the light-emitting element floats after soldering, and a good electrical connection between the chip electrode and the wiring pattern of the substrate There is a problem that cannot be obtained. In addition, even if electrical connection is obtained, the device becomes thick as much as the light emitting element is lifted from the substrate, and the device cannot be sufficiently thinned.
[0007]
By the way, when the chip is a light emitting element such as an LED (Light Emitting Diode), conventionally, the electrode of the light emitting element is an alloy of gold (Au) and a small amount of zinc (Zn) or Au and a small amount of silicon (Si). In view of this material, solder that does not contain tin, for example, solder (InPb) made of indium (In) and lead (Pn) is used. This is because most or all of the electrodes of the light emitting element are consumed by the tin, that is, they are dissolved. However, solder made of indium and lead is more difficult to handle because it is more easily oxidized than solder containing tin, and in addition, there is a problem that the device manufacturing cost is high because it is expensive.
[0008]
Accordingly, an object of the present invention is to prevent the chip from being lifted from the solder when the chip is soldered to the substrate by the reflow method, even if the chip is a small and light chip such as a light emitting element. It is an object of the present invention to provide a soldering method for a chip that can be soldered using a solder containing tin in the case of a light emitting element.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, a chip soldering method according to the present invention includes a wiring pattern in which electrodes formed on both sides of a chip which is a light emitting element are formed on the surface of a substrate. A method of soldering a chip to be soldered to the substrate, wherein the chip is fixed to the surface of the substrate so that the electrode faces the surface of the substrate exposed between the wiring patterns, and then the solder is applied to the electrode. supplied, after heated and melted the solder, cooled to solidify again, the electrode is an alloy film comprising Au and Zn and Ni, the solder is characterized by Rukoto contain tin.
[0010]
Since the chip is fixed to the substrate, the chip does not move relative to the substrate during the reflow soldering process. Therefore, the chip does not float. As a result, a good electrical connection can be obtained between the chip and the substrate.
[0011]
The chip soldering method of the above configuration can be applied to all types of chips, but is particularly effective for small and light chips such as light emitting elements.
[0012]
When the chip is a light-emitting element such as an LED, the results of experiments on electrode materials conducted by the inventors have shown that the electrode of the light-emitting element is made of an alloy film containing gold (Au), zinc (Zn), and nickel (Ni). It has been found that the amount of electrode consumed is small even when solder containing tin is used. Therefore, solder containing tin can be used. A solder containing tin is easier to handle and less expensive than a solder made of indium and lead, which has been used for soldering of a light emitting element in the past, so that the manufacturing cost can be reduced.
[0013]
In this chip soldering method, the solder can be supplied to the electrode of the chip, for example, by any of the following methods.
[0014]
The first method is a method of applying the solder to the chip and the electrode so as to cover the chip and the electrode with cream-like solder using a printing mask having an opening exposing the chip and the electrode. This method is effective when soldering a large number of chips arranged on a substrate. Solder can be applied to all the chips at once by simply providing the openings of the printing mask in alignment with the positions of all the chips. The solder application amount can be controlled by changing the opening diameter and thickness of the printing mask.
[0015]
The second method is a method of supplying cream solder using a dispenser. Although this method cannot solder a large number of chips at once as in the case of using a printing mask, since it uses a dispenser, it is easier to control the amount of solder supplied than in the case of using a printing mask. It can be done.
[0016]
Furthermore, the present invention provides a soldering method that specifically targets a light emitting element such as an LED as a chip connected to a substrate. In this soldering method, as described in claim 5, after fixing a chip of a light emitting element having an electrode made of an alloy film containing Au, Zn, and Ni to a substrate, the substrate on which the chip is fixed is made of tin. It is characterized by being immersed in a solder dip bath.
[0017]
This soldering method is a so-called dip method, and this method is possible because the chip is fixed to the substrate. When the dip method is used, a plurality of chips, that is, light emitting elements can be soldered in a single time. Further, since the electrode of the light emitting element is formed of an alloy film containing Au, Zn, and Ni, solder containing tin can be used in this way. In addition, since the solder contains tin, it is easier to handle and less expensive than the solder not containing tin, which has been used for soldering the light emitting element in the past, so that the device manufacturing cost can be reduced.
[0018]
In any of the above-described soldering methods of the present invention, the chip is preferably fixed to the substrate using an epoxy adhesive. Epoxy adhesives cure at 120 ° C. in about 1 minute. Moreover, even if it is attached to a 260 ° C. solder solution, the element can be held on the substrate for about 10 seconds. Therefore, use of an epoxy adhesive is suitable for fixing elements for soldering including solder dip. When soldering by the reflow method, the reflow time (heating time) is as long as about 1 minute, and during this time the epoxy adhesive softens, but the substrate is kept horizontal. Therefore, the softening of the adhesive does not significantly shift the chip in the horizontal direction with respect to the substrate.
[0019]
The adhesive may be applied to the substrate using a screen mask, or may be applied to the substrate using a dispenser while controlling the amount of the adhesive. When a screen mask is used, an adhesive can be printed at a plurality of locations at once, so this coating method is effective when it is desired to arrange chips in a matrix on a substrate. On the other hand, when a dispenser is used, the amount of adhesive applied can be easily controlled.
[0020]
When the chip is formed of a light emitting element (LED), examples of the substrate on which the chip is mounted include a chip-shaped LED substrate, a dot matrix unit substrate, and a numerical display substrate. When a chip is mounted on a chip-type LED substrate by this method, a thin chip-type LED is realized because no wire is required in the chip portion. In addition, when a dot matrix unit substrate is used, since no wires are required for the LED portion of the dot matrix, the dot matrix can be made highly precise (chip pitch is 1.5 mm or less). In addition, when a numerical display substrate is used, since a wire is not necessary for the chip portion, the numerical display can be made thin.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
(First embodiment)
FIG. 1 is a process diagram showing a chip soldering method according to a first embodiment of the present invention. The chip soldering method will be described below with reference to FIG.
[0022]
First, a chip 1 to be contacted by soldering, a printed board 3 for mounting the chip, and a thermosetting adhesive 5 are prepared. In the present embodiment, a light emitting diode (LED) which is an example of a light emitting element is used as the chip 1. Electrodes 11 made of an alloy film of AuZn and Ni are formed on both sides of the LED. A wiring pattern 7 made of Au is formed on the substrate 3. As the substrate 3, a chip-type LED substrate, a dot matrix unit substrate, a numeric display substrate, or the like is used. In FIG. 1, only one chip 1 is shown for simplicity, but a necessary number is prepared according to the type of substrate. The adhesive is preferably an epoxy adhesive because it can withstand the reflow temperature for a short time (about 10 seconds). For example, NE8800K manufactured by Toa Gosei can be used. The epoxy adhesive is cured by heating at 120 ° C. for about 1 minute.
[0023]
After preparing the above materials, the chip 1 is fixed on a substrate as shown in FIG. This fixing is performed as follows. First, the adhesive 5 is applied to the chip mounting position between the wiring pattern 7 and the wiring pattern 7 on the substrate 3. As a coating method, when a large number of chips are to be arranged, for example, in a matrix, it is preferable to use a screen mask at a plurality of locations at once to reduce time, and to apply an adhesive. If application is desired while controlling the amount, the method using a dispenser may be easily controlled. An appropriate coating method may be selected according to the purpose. After the adhesive 5 is applied to the substrate 3 in this way, the chip 1 is placed on the adhesive 5. At this time, the chip, that is, the LED 1 is placed sideways so that the PN junction surface is perpendicular to the substrate 3. Subsequently, the adhesive 5 is thermally cured in an oven. The curing conditions were 150 ° C. and 5 minutes. The chip 1 is firmly fixed on the substrate by the heat curing of the adhesive.
[0024]
Next, the electrodes 11 at both ends of the chip and the wiring pattern 7 on the substrate are connected by solder containing tin, that is, soldering is performed. Here, a connection method by solder reflow using cream solder S will be described. The solder S used here is a solder made of tin and lead.
[0025]
First, as shown in FIG. 1B, a printing mask having an opening at a position corresponding to a chip mounting position, that is, a metal mask 9 for solder printing is placed on the substrate 3. At this time, the metal mask 9 is made thicker than the chip 1. Then, as shown in FIGS. 1C and 1D, solder S is printed in the opening of the metal mask 9 using the squeegee 13. As a result, the solder S is applied while covering the entire chip 1. In the case of the coating method using this metal mask, the coating amount can be controlled by changing the hole diameter of the metal mask, that is, the dimension of the opening or the thickness of the metal mask.
[0026]
Next, as shown in FIG. 1E, the metal mask 9 is removed from the substrate. Then, the chip mounting substrate on which the cream-like solder S has been applied is passed through a solder reflow furnace (not shown), and the solder S is heated and melted, then cooled and solidified, and the solder connection structure shown in FIG. Get. The heating temperature (reflow temperature) at this time differs depending on the melting point of the solder, but in this embodiment, solder having a melting point of 240 ° C. was used, and the heating temperature in the reflow furnace was 256 ° C. The heating time was on the order of 1 minute. In this reflow process, even if convection occurs when the solder S melts, the chip 1 is fixed to the substrate with the adhesive 5, so that the floating problem caused by the lightness of the chip that can occur in the conventional method. Is avoided. Therefore, a thin SMD (Surface Mounting Device) type LED can be obtained. The adhesive 5 softens when the heating time exceeds about 10 seconds. However, since the substrate is held horizontally, there is substantially no problem with respect to the holding ability of the chip. Further, although the solder S contains tin, since the material of the electrode 11 is an alloy containing Au, Zn, and Ni, it is hardly dissolved by the tin of the solder.
[0027]
What is important here is that if the resulting device is a chip-type component, and this chip-type component is soldered to another board on the user side, the solder S is the solder used on the user side. It is necessary to have a melting point higher than the reflow temperature. This is because if the melting point of the solder S is lower than the reflow temperature on the user side, the solder S is melted during the solder reflow process on the user side, and the electrical connection of the chip 1 may be opened. Because.
[0028]
Next, a method for forming the electrode 11 of the light emitting diode 1 will be described with reference to FIG. FIG. 4 is an electrode cross-sectional view. First, an AuZn film, an Ni film, and an AuZn film are sequentially formed on a semiconductor wafer to obtain a stacked body 11 ′. Thereafter, this laminated body 11 ′ is heat-treated to obtain an electrode 11 made of a single layer alloy film of AuZn and Ni.
[0029]
When the inventor conducted a soldering experiment using SnPb using the electrode 11 ′ before heat treatment and the electrode 11 after heat treatment, the electrode structure before heat treatment consumed a large amount of electrode. In this electrode structure, the electrode consumption was small. Similar results can be obtained by replacing the AuZn film below the Ni film with an alloy of gold and beryllium (Be) (AuBe) or an alloy of gold and silicon (Si) (AuSi). It was.
[0030]
The case where an LED is used as the chip 1 has been described above, but it will be apparent that this embodiment can be applied to any type of chip. Moreover, although the thing containing tin was used as the solder S, what is necessary is just to select an appropriate thing considering the material of the electrode of a chip | tip, and a wiring pattern as the material of solder. Further, the structure of the electrode 11 can be applied to a chip other than the light emitting element as required.
[0031]
(Second Embodiment)
FIG. 2 is a process diagram showing a chip mounting method according to the second embodiment of the present invention. This embodiment differs from the first embodiment in that solder is applied using a dispenser, whereas the first embodiment applies solder using a printing metal mask. That is, only the solder application method is different from the first embodiment. The other points are the same as those of the first embodiment.
[0032]
First, the LED chip 1 is fixed on the substrate 3 with an adhesive 5 as shown in FIG. The process shown in FIG. 2A is the same as the process shown in FIG.
[0033]
Subsequently, as shown in FIGS. 2B to 2D, cream-like solder S is applied between the electrode 11 on each side of the chip and the wiring pattern 7 of the substrate 3 using the dispenser 15. When the dispenser 15 is used in this way, the application amount can be easily controlled.
[0034]
Next, the substrate 3 coated with cream-like solder S on both sides of the chip 1 is passed through a solder reflow furnace (not shown), the solder S is heated and melted, and then cooled and solidified, as shown in FIG. The solder connection structure shown is obtained.
[0035]
Also in the second embodiment, as in the case of the first embodiment, any chip other than the light emitting element can be used as the chip 1. Moreover, although the thing containing tin was used as the solder S, what is necessary is just to select a suitable solder material considering the material of the electrode of a chip | tip and a wiring pattern.
(Third embodiment)
FIG. 3 is a process diagram showing a soldering method for a light emitting device according to a third embodiment of the present invention. This embodiment is different from the first and second embodiments in that cream-like solder is applied and melted and solidified, whereas the first and second embodiments are immersed in liquid solder and soldered. This is different from the second embodiment. In other respects, the material of the electrode 11 of the chip 1, the material of the wiring pattern 7, and the material of the solder S are the same as those in the first and second embodiments.
[0036]
First, an LED chip 1 as a light emitting element is fixed on a substrate 3 with an epoxy adhesive 5 as shown in FIG. Since the process shown in FIG. 3A is the same as the process shown in FIG.
[0037]
Next, the chip / substrate assembly in which the chip 1 is fixed to the substrate 3 is immersed in a solder dip tank 17 containing, for example, solder S that has been heated to 260 ° C. to form a liquid, and soldering the chip 1 To do. At this time, the epoxy adhesive 5 fixing the chip 1 to the substrate 3 can hold the chip 1 for about 10 seconds even if it is immersed in a 260 ° C. solder solution. There is no possibility of displacement with respect to 3. Moreover, although the solder S contains tin, since the material of the electrode 11 is an alloy containing Au, Zn, and Ni, it cannot be melted by the solder tin. As a result of soldering by dipping (immersion), the solder connection structure shown in FIG. 3C is obtained.
[0038]
The soldering by this dip method has the advantage that the number of processes is very small and the soldering can be performed easily and in a single time.
[0039]
【The invention's effect】
As is apparent from the above description, the chip soldering method according to the present invention is as described in claim 1, after the chip is fixed to the substrate, the solder is supplied to the electrode of the chip, and the solder is heated and melted. Then, it cools and solidifies again. That is, reflow soldering is performed with the chip fixed to the substrate. Therefore, the chip does not move with respect to the substrate during the soldering process, and therefore, even if the chip is small and light, the chip does not float, thus obtaining a good electrical connection between the chip and the substrate. be able to.
[0040]
Furthermore, according to another soldering method of the present invention, the chip of the light emitting device having an electrode made of an alloy film containing Au, Zn, and Ni is fixed to the substrate, and then the chip is mounted. Since the fixed substrate is immersed in a dip bath of solder containing tin, a plurality of chips, that is, light emitting elements can be soldered in a single time, and since the solder contains tin, conventional soldering of light emitting elements is possible. Compared to the tin-free solder that has been used, it is easy to handle and inexpensive, so the device manufacturing cost can be reduced.
[0041]
By using the present invention, it is possible to easily and inexpensively reduce the thickness of an SMD type LED that is becoming the mainstream of LED lamps.
[Brief description of the drawings]
FIG. 1 is a process diagram showing a chip soldering method according to a first embodiment of the present invention.
FIG. 2 is a process diagram showing a chip soldering method according to a second embodiment of the present invention.
FIG. 3 is a process diagram showing a chip soldering method according to a third embodiment of the present invention.
FIG. 4 is a cross-sectional view illustrating a method for forming an electrode of a chip used in each of the embodiments of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Chip, 3 ... Board | substrate, 5 ... Adhesive, 7 ... Wiring pattern, 9 ... Print mask, 11 ... Electrode, 15 ... Dispenser, 17 ... Solder dip tank, S ... Solder.

Claims (6)

A chip soldering method for soldering electrodes formed on both sides of a chip as a light emitting element to a wiring pattern formed on a surface of a substrate,
After fixing the chip to the surface of the substrate so that the electrode faces the surface of the substrate exposed from between the wiring patterns, solder is supplied to the electrode, the solder is heated and melted, and then cooled. Solidify again ,
The electrode is made of an alloy film containing Au and Zn and Ni, soldering method of the chip the solder, characterized in Rukoto contain tin. 2. The chip soldering method according to claim 1, wherein the chip and the electrode are covered with cream-like solder using a printing mask having an opening exposing the chip and the electrode. A method of soldering a chip, wherein the solder is applied to the chip. 2. The chip soldering method according to claim 1, wherein cream-like solder is supplied using a dispenser.   A chip of a light-emitting element having an electrode made of an alloy film containing Au, Zn, and Ni is fixed to a substrate, and then the substrate on which the chip is fixed is immersed in a dip bath of solder containing tin. Soldering method. In soldering method according chips to any one of claims 1 to 4, fixed to the substrate of the chip, soldering method of the chip, characterized in that carried out using an epoxy adhesive. 6. The chip soldering method according to claim 5 , wherein the adhesive is applied to the substrate using a screen mask.

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