WO2009110414A1 - Method for forming bump - Google Patents

Abstract

Total discharge amount of silver nano ink droplets (31) for the first time (initial stage) is set in the range of 1/1.1-1/10 of total discharge amount of silver nano ink droplets (32) for the second and subsequent times on an electrode (2) formed on a substrate (1). Temperature of the substrate (1) during discharge for the first time (initial stage) is set higher than the temperature of the substrate (1) during discharge for the second and subsequent times (subsequent to initial stage). Since spread of the lower layer of a bump on the electrode (2) is limited and a bump is formed in a limited region, reduction in size of a pad formed on an electrode and reduction in pitch of the pads can be dealt with.

Description

Bump formation method

The present invention relates to a bump forming method for forming bumps for mounting on a substrate or for electrical connection with other electronic components by a droplet discharge method of a metal dispersion.

Patent Document 1 discloses a bump forming method used when a semiconductor device is mounted on a substrate, and a metal dispersion obtained by dispersing metal fine particles in a bump forming portion of the substrate or the semiconductor device is a droplet discharge method. Then, a bump forming method is disclosed in which a metal dispersion provided in a bump forming section is heat treated to form a metal bump.

According to this bump forming method, the metal dispersion is discharged to the bump forming portion by the droplet discharge method and further heat-treated to form the bump, so that no particularly expensive apparatus is required and the number of steps The number of types of equipment can be reduced, and consumables such as photomasks are not required. Costs are significantly reduced compared to conventional methods. Therefore, it is said that there is almost no waste of material, and that there is almost no industrial waste such as waste liquid.

Also, in this bump forming method, the number of droplet discharges when the metal dispersion is provided by the droplet discharge method is set to a plurality of times, and the droplet discharge amount at one time is different from the droplet discharge amount at another time. It is also disclosed that bumps having different outer diameters are formed at least at the lower part and the upper part.

Patent Document 2 discloses an electronic component manufacturing method including a step of providing a three-dimensional structure above a substrate, and discharging a liquid composition containing a conductive material, drying the composition, and discharging the conductive material above the substrate. A first step of forming the first layer, and a second step of discharging the composition containing the conductive material onto the first layer and drying the composition to form the second layer of the conductive material. And a method for manufacturing an electronic component.

According to this electronic component manufacturing method, a desired three-dimensional structure can be obtained by laminating the first layer and the second layer that form a part of the three-dimensional structure, and the first layer When forming the second layer, for example, by discharging a composition droplet by a droplet coating method using a mechanism similar to that of an inkjet printer, drying and solidifying, a process like a photolithography It is said that there is an effect that a fine three-dimensional structure can be formed in a small number of steps and at a low cost without increasing the number.

In addition, in this electronic component manufacturing method, it is disclosed that the second discharge amount is smaller than the first discharge amount. By doing in this way, even if a shift occurs between the position where the composition is discharged in the first step and the position where the composition is discharged in the second step, the second layer does not protrude from the first layer. It is possible to form a layer, and it is possible to prevent problems such as the composition discharged in the second step dripping from the first layer and losing its shape, or the height accuracy is reduced. Even if the tip of the formed three-dimensional structure is pressed and the second layer is deformed, it does not protrude from the first layer, so the possibility of short-circuiting with the adjacent three-dimensional structure is reduced, and the three-dimensional structure is It is said that it is possible to arrange with a narrow pitch.
JP 2004-228375 A JP 2003-218149 A

Here, the wet spread diameter after landing of the metal dispersion is considered.
Patent Documents 1 and 2 show that the discharge amount is intentionally changed to form bumps having different diameters at the upper part and the lower part, in particular, the lower part has a wider diameter. Even if the first discharge amount is equal to the second discharge amount (even more than that), the first discharge after the metal dispersion liquid has spread on the electrode and the second and subsequent discharges. The metal dispersion discharged on the first layer does not spread as much as the first time on the dry film of the metal dispersion, but accumulates within the inner area, resulting in the formation of bumps having a hem-extended shape. I obtained the knowledge that

FIG. 1 shows how bumps are formed by discharging droplets of a metal dispersion. In FIG. 1, a partial cross-sectional notation of the cut surface is omitted.

FIG. 1A shows a state in which metal dispersion droplets 13 are ejected from the droplet ejection head 10 to the electrode 2 formed on the upper surface of the substrate 1. FIG. 1B shows a state in which bumps 14 are formed in which the ejected metal dispersion droplets have landed on the surface of the electrode 2 and have spread. FIG. 1C shows a cross-sectional shape of a bump formed by performing heat treatment after ejecting metal dispersed droplets in a plurality of times.

As described above, the central discharge portion 14b protruding in the thickness direction is formed with respect to the upper surface of the bottom surface portion 14a of the bump 14 wetted and spread (a skirt portion when the bump is compared to a mountain), but the diameter of the bottom surface portion is small. Since a large bump is formed, this becomes a very big problem in reducing the pad size of the electrode for forming the bump and narrowing the pitch of the bump.

Therefore, an object of the present invention is to provide a bump forming method adapted to the reduction in the size of the pads for forming the bumps and the reduction in the pitch of the bumps without increasing the diameter of the bottom surface.

Although the details of the above phenomenon are unknown, it is considered that the wetting and spreading diameter of the metal dispersion droplet is determined by the material / discharge speed of the metal dispersion droplet, the material / surface roughness of the landing portion, etc. . Therefore, the following mechanism can be considered as the cause of the above phenomenon.

That is, the electrode surface has irregularities, and the metal dispersion droplet ejected for the first time has a small contact angle with respect to the electrode surface and spreads easily.

The metal dispersion droplets discharged after the second time are formed on the already formed dry film of the metal dispersion (film that has been dried to a certain extent), but the first dry film of the metal dispersion is an electrode. Since the surface is in a smooth state, the contact angle of the metal dispersion droplet is large. In other words, it does not spread as much as the first time, but is stacked on top.

In the third and subsequent times, as in the second time, the metal dispersion gradually accumulates on top.

In this way, the wetting spread on the metal dispersion dry film by the second and subsequent discharges is smaller than the wetting spread on the electrode of the metal dispersion discharged the first time, resulting in the shape of the tail spread. It is thought that the bump which has is formed.

Therefore, the present invention forms bumps by the following method.
(1) When a metal dispersion liquid droplet is ejected onto an electrode formed on a substrate to form a bump made of metal dispersed in the metal dispersion liquid, the metal dispersion liquid droplet is used as an initial stage. The discharge is divided into the subsequent stages, and the discharge amount in the initial stage is set to be smaller than the discharge amount in the subsequent stage.

(2) Alternatively, the temperature of the substrate in the initial stage is set higher than the temperature of the substrate in the subsequent stage.
(3) Furthermore, when a metal dispersion liquid droplet is ejected onto the electrode formed on the substrate to form a bump made of metal dispersed in the metal dispersion liquid, the metal dispersion liquid droplet is Discharge is divided into an initial stage and subsequent stages, and the substrate temperature in the initial stage is set higher than the substrate temperature in the subsequent stage, and the discharge amount in the initial stage is set in the subsequent stage. Smaller than the discharge amount.

In any of the above (1) to (3), the wetting and spreading of the metal dispersion discharged in the initial stage onto the substrate electrode is suppressed, and the metal dispersion discharged in the subsequent stage is suppressed in the initial stage. It is piled up without spreading greatly wet on the film of the discharged metal dispersion. As a result, a bump having a small diameter at the bottom is formed.

(4) In the discharge in the initial stage and the subsequent stage, a plurality of droplets are sequentially discharged, and the discharge amount in the initial stage and the discharge amount in the subsequent stage are respectively determined by the number of discharges. You may do it.

Thus, instead of controlling the amount of droplets ejected at one time, the number of ejections, that is, the discrete amount is controlled, and the overall control becomes easy. In addition, the accuracy of the total discharge amount at each stage is increased, and the bump profile (cross-sectional shape) can be determined with high accuracy.

(5) The solvent contained in the metal dispersion is preferably an organic solvent having a boiling point of 200 ° C. or higher. As a result, the drying of the organic solvent proceeds slowly, so that the deposited metal dispersion has less volume shrinkage on the previously deposited metal dispersion, and the bumps accumulate more efficiently in the height direction.

According to the present invention, it is possible to form a bump having a shape suitable for a reduction in the size of the electrode for forming the bump and a reduction in the pitch of the bump without increasing the diameter of the bottom surface. For this reason, there is an effect that it is easy to manufacture an electronic component device using a small semiconductor chip in which electrode pads are particularly small and it is necessary to form bumps with a narrow pitch.

In addition, wetting and spreading of the liquid droplets of the metal dispersion liquid on the substrate electrode is greatly suppressed, and it is possible to cope with a smaller electrode pad and a narrow pitch without changing the total ink supply amount.

It is a figure which shows the example of the bump formation method by a prior art, and the shape of a bump by it. It is a figure which shows the procedure of the bump formation method which concerns on 1st Embodiment. It is a plane photograph which shows the shape of the bump formed by the bump formation method concerning a 1st embodiment, and the bump by a prior art.

Explanation of symbols

1-substrate 2-electrode 10-droplet discharge head 13-metal dispersion droplet 14-bump 14a-bottom portion 14b-center protrusion 15-bump 31,32-silver nano ink droplet 41-bump lower layer portion 51-55-bump Upper echelon

<< First Embodiment >>
FIG. 2 is a diagram illustrating a procedure of the bump forming method according to the first embodiment. In FIG. 2, the cross-sectional notation of a part of the cut surface is omitted. The substrate 1 is, for example, a ceramic substrate, and a gold (Au) electrode 2 is previously formed on the upper surface thereof. As the metal dispersion for forming the bump, a silver nanoink having a low viscosity of about 5 to 50 mPa · s in which silver (Ag) nanoparticles are dispersed in a solvent is used. Then, droplets are ejected a plurality of times on the upper portion of the electrode 2 by an ink jet method using the droplet ejection head 10, and a layer formed by the landing of silver nano ink droplets is stacked.

At that time, the temperature of the substrate is set in a range of 20 to 100 ° C., for example, so that the silver nano-ink is dried for a plurality of times and the dried layers are sequentially stacked.

The silver nano ink is obtained by coating the surface of silver fine particles having an average particle diameter of 1 to 100 nm with a dispersing agent such as amine, alcohol, and thiol capable of coordinating with silver element, and stably dispersing in an organic solvent. . In this silver nano ink, silver nanoparticles are stably dispersed in the organic solvent without being aggregated in the organic solvent by the coating action of the dispersant. During heating, a scavenger such as an acid anhydride takes up the dispersant. And it conducts, for example, by sintering at a low temperature of 250 ° C. or lower to form a junction.
In addition, as a metal nanoparticle, gold | metal | money and copper can also be used besides silver.

First, as shown in FIG. 2A, a plurality of silver nanoink droplets with a total supply amount of 40 pl are ejected onto the surface of the electrode 2 for the first time (initial stage). The time interval between the plurality of silver nano ink droplets 31 is about 1 μs to 1 ms.

Thereby, as shown in FIG. 2B, a bump lower layer portion 41 is formed on the surface of the electrode 2 by the deposition of the silver nano ink droplet 31. The temperature of the substrate 1 and the electrode 2 is 50 ° C. throughout the entire process, and in a few tens of seconds, the solvent in the ink evaporates and the viscosity of the bump lower layer 41 is increased and dried.

The formation of the bump lower layer portion 41 is sequentially performed on each electrode 2 by scanning of a droplet discharge head or scanning of the substrate 1. This scanning is performed in a two-dimensional direction. For example, the substrate 1 may be scanned in the X-axis direction and the droplet discharge head 10 may be scanned in the Y-axis direction.

After a predetermined time or more has elapsed since the deposition of the silver nano ink droplets, as shown in FIG. 2C, silver nano ink droplets having a total supply amount of 200 pl are ejected as the second ejection. That is, the silver nano ink droplets 32 are deposited on the surface of the bump lower layer portion 41 that has already been dried. Thereby, the bump upper layer portion 51 is formed on the surface of the bump lower layer portion 41 as shown in FIG.

It is desirable to use an organic solvent having a boiling point of 200 ° C. or higher for the silver nano ink droplets. As a result, the drying of the organic solvent proceeds slowly, so that the deposited metal dispersion has less volume shrinkage on the previously deposited metal dispersion, and the bumps accumulate more efficiently in the height direction. become.

Examples of the organic solvent having a boiling point of 200 ° C. or higher include dodecane (boiling point 215 ° C.), tridecane (boiling point 234 ° C.), tetradecane (boiling point 254 ° C.), pentadecane (boiling point 271 ° C.), and the like.

In the subsequent third and subsequent times, similarly to the second time, a plurality of silver nano ink droplets with a total supply amount of 200 pl are ejected onto the surface of the electrode 2 at intervals of a predetermined time or more. As a result, bump upper layer portions 52 to 55 are sequentially formed as shown in FIG.

The first and second discharge time intervals and the subsequent discharge time intervals are in the range of 1 ms to 600 s so that the silver nanoink is dried and the dried layers are stacked when the silver nanoink is discharged a plurality of times. Set. The time interval of each time is not limited to being the same, and may be different.

In addition, the ratio of the total supply amount of the silver nano-ink from the first time to the second time depends on the discharge amount of the first time, and when the total supply amount of the first time is 1 to 1000 pl, the total supply amount of the second and subsequent times Is set in the range of about 1.1 to 10 times the first time. This ratio is determined so that the wetting and spreading of the silver nano-ink after the second time becomes smaller than the first time.

In the second and subsequent discharges of silver nanoink droplets, it is made on the dry film of silver nanoink that has already been formed, but the dry film of silver nanoink is smoother than the electrode surface, and the contact angle of silver nanoink is large, Silver nano-ink does not spread as much as the first time, and will be stacked on top. Therefore, even though the supply amount is greater than the first time, it does not spread as much as the first time. Therefore, as shown in FIG. 2D, the bump upper layer portion 51 is stacked on the bump lower layer portion 41.

Also, the later the discharge times, the more smooth the dry film surface of the silver nano-ink and the less wetting and spreading, and the corresponding thickness increases. Therefore, as shown in FIG. 2 (E), the cross-sectional shape of the bump is a tapered mountain shape even though the total supply amount at one time is the same.

Thereafter, the entire substrate is heated to a predetermined temperature of 250 ° C. or lower to sinter the bumps at a low temperature. As a result, as shown in FIG. 2 (F), silver particles are sintered and bonded together, and a silver bump bonded to the electrode 2 is formed.

It should be noted that the above-described ejection of the silver nano ink may be performed for all the necessary times in the same manner for another adjacent electrode after performing the necessary number of times for one electrode. According to this method, there are advantages that the stacking deviation of each layer formed by the deposition of silver nano ink is reduced and the number of times the droplet discharge head or the substrate is moved is reduced. In addition, according to the method of performing scanning sequentially for every electrode as described above, since the layer of silver nanoink that has already landed progresses during scanning and ejection to another electrode, the silver nanoink There is an advantage that the time required for drying can be earned.

FIG. 3 is a plane photograph showing the shape of bumps formed by the bump forming method shown in the first embodiment and bumps according to the prior art.
FIG. 3A shows bumps according to the first embodiment in which 200 pl of silver nano-ink droplets are ejected 40 pl at the first time, and 200 pl each time from the second time to the sixth time, and the bump lower layer portion 41 is 200 to 200 on the surface of the electrode 2. It can be seen that it has spread by 250 μm. Further, it can be seen that the upper layer portion 55 of the bump is deposited on the upper portion of the lower layer portion 41 of the bump, and the upper layer portion 55 of the silver nano-ink is deposited for the second and subsequent times.

FIG. 3B shows an example in which 200 pl of silver nano ink droplets are ejected from the first to the sixth time, and it can be seen that the bottom surface portion 14a of the bump due to the first deposition of the silver nano ink spreads by 500 μm or more. Therefore, in this example, the pad width of the electrode for forming the bump cannot be made 500 μm or less. On the other hand, in the example shown in FIG. 3A, the pad width of the electrode for forming the bump can be reduced to about 300 μm, and the bump can be narrowed accordingly.

After forming silver bumps as described above, parts in a predetermined chip state or substrate state are bonded through the bumps. Thereafter, the substrate 1 is divided to obtain individual electronic components. Alternatively, after the formation of silver bumps (ie, before heating), after bonding parts in a predetermined chip state or substrate state, the entire substrate is heated to a predetermined temperature of 250 ° C. or less, and the silver bumps are sintered to form a bonded portion. May be formed.

In the example shown above, silver bumps were formed on the gold electrode formed on the ceramic substrate. However, the silver bumps were formed on a semiconductor substrate such as a silicon wafer, a resin substrate, a lead frame, and a film. The same applies to tapes and semiconductor chips. Further, the present invention can be similarly applied when silver or copper is used in addition to gold as an electrode for forming a silver bump.

<< Second Embodiment >>
In the first embodiment, the temperature of the substrate and the electrode is constant, but in the second embodiment, the substrate temperature at the time of discharging the first silver nanoink droplet is set to a high value of, for example, 70 ° C. The substrate temperature during discharge is 50 ° C.

Suppose that the supply amount at each discharge is constant at 200 pl.

As a result, as shown in FIG. 3 in the first embodiment, it is possible to form a bump in which the spread of the bottom portion (bottom portion) is suppressed.

<< Third Embodiment >>
In the third embodiment, the discharge amount control shown in the first embodiment is combined with the substrate temperature control shown in the second embodiment. For example, the first discharge amount is 100 pl, the substrate temperature is 60 ° C., the second and subsequent discharge amounts are 200 pl, and the substrate temperature is 50 ° C.

Thereby, the drying time by evaporation of the organic solvent in the lower layer of the bump can be shortened, and the time required for forming the bump having the required height can be shortened.

In the example shown above, silver nano ink is used as the bump material. However, in addition to such a metal dispersion, a non-metal dispersion or a resin dispersion such as a resistance paste or a photoresist may be used. Good. In addition to the bumps, the present invention can be similarly applied to the case where electrode wirings are formed at a narrow pitch.

Claims (5)

A method of discharging a droplet of a metal dispersion liquid onto an electrode formed on a substrate to form a bump made of metal dispersed in the metal dispersion liquid,
Bump formation characterized in that droplets of the metal dispersion liquid are ejected separately in an initial stage and subsequent stages, and the ejection amount in the initial stage is smaller than the ejection amount in the subsequent stage Method. A method of discharging a droplet of a metal dispersion liquid onto an electrode formed on a substrate to form a bump made of metal dispersed in the metal dispersion liquid,
The metal dispersion liquid droplets are ejected separately in an initial stage and subsequent stages, and the temperature of the substrate in the initial stage is set higher than the temperature of the substrate in the subsequent stage. Bump formation method. A method of discharging a droplet of a metal dispersion liquid onto an electrode formed on a substrate to form a bump made of metal dispersed in the metal dispersion liquid,
The droplets of the metal dispersion liquid are ejected separately in an initial stage and subsequent stages, and the temperature of the substrate in the initial stage is set higher than the temperature of the substrate in the subsequent stage. The bump forming method is characterized in that the discharge amount is made smaller than the discharge amount in the subsequent stage. The discharge of the liquid droplets of the metal dispersion liquid in the initial stage and the subsequent stage is to sequentially discharge a plurality of liquid droplets. The discharge amount in the initial stage and the subsequent stage are determined depending on the number of discharges. 4. The bump forming method according to claim 1, wherein a discharge amount is determined. 5. The bump forming method according to claim 1, wherein the solvent contained in the metal dispersion is an organic solvent having a boiling point of 200 ° C. or higher.

Images