JP5037406B2 - Conductive adhesive and flip chip bonding method using the same - Google Patents

Description

  The present invention relates to a conductive adhesive and a flip-chip bonding method using the same, and more particularly, a conductive adhesive including non-conductive balls for adjusting a distance between a semiconductor chip and a substrate and a flip using the same. The present invention relates to a chip bonding method.

  Electronic packaging technology is a wide and diverse system manufacturing technology that includes all stages from semiconductor devices to final finished products. Recently, the rapidly developing semiconductor technology has already integrated more than 1 million cells, and in the case of non-memory devices, it has a large number of I / O pins, a large die size, a large heat dissipation, The trend is toward high electrical performance. However, there is a fact that electronic packaging technology for packaging such devices is not in line with the rapid semiconductor industry. Electronic packaging technology is a very important technology that determines the performance, size, price, reliability, etc. of the final electronic product, especially high electrical performance, ultra-small / high density, low power, multi-function, ultra-high speed In recent electronic products that pursue signal processing, permanent reliability, etc., the phase has become more important.

  In conjunction with this trend, in recent years, flip chip bonding technology, which is one of the technologies for electrically connecting a semiconductor chip to a substrate without using leads, has attracted attention. (For example, refer to Patent Document 1). In a flip chip bonding process, a conductive adhesive used for bonding a semiconductor chip to a substrate is generally composed of a solder which is a conductive particle and an insulating resin having thermosetting and / or thermoplastic properties. .

  Recently, a conductive adhesive containing a low-melting-point solder having a low melting point has been widely used in order to enhance electrical coupling between a semiconductor chip and a substrate (for example, see Non-Patent Document 1). In the flip chip bonding method, the low melting point solder particles are melted and fused together as the temperature increases, and the wetting property of the low melting point solder wets between the electrode of the semiconductor chip and the electrode of the substrate. ) To electrically connect the electrodes. At this time, in order for the low melting point solder particles to be sufficiently fused and wetted, the distance between the electrode of the semiconductor chip and the electrode of the substrate must be maintained at a constant interval for a predetermined time.

In the conventional flip chip bonding method, a separate stand-off is formed on the surface of the substrate, so that the distance between the semiconductor chip and the substrate is maintained by the stand-off during fusion and wetting of the low melting point solder. To get. However, the conventional flip chip bonding method has a disadvantage in that it requires expensive bonding equipment and sophisticated control technology to form a standoff.
Korean Patent Publication No. 1998-013961 New Electrically Conductive Adhesives Filled With Low-Melting-Point Alloy Fillers 1Department of Manufacturing Science, Graduate School of Engineering, Osaka University, Suita 565-0871, Japan2Sakaiko Power Plant, Kansai Electric Power Co. Ltd., Osaka 530-8270, Japan

  An object of the present invention is to provide a conductive adhesive capable of performing a flip chip bonding process using a low melting point solder at a low cost without a high level of control technology, and a flip chip bonding method using the same.

  In order to achieve the above object, a conductive adhesive according to one embodiment of the present invention includes a thermosetting polymer resin, a low-melting solder ball dispersed in the polymer resin, and the polymer resin. And non-conductive balls which are dispersed and have a melting point higher than the melting point of the low melting point solder balls.

  Also, in the flip chip bonding method according to another aspect of the present invention, a conductive adhesive including a low melting point solder ball, a polymer resin, a first non-conductive ball, and a second non-conductive ball is prepared on the substrate. Applying a predetermined first pressure between the semiconductor chip and the substrate at a first temperature higher than a melting point of the low melting point solder ball; aligning the electrodes of the semiconductor chip and the electrodes of the substrate; And applying a second pressure higher than the first pressure between the semiconductor chip and the substrate at a second temperature higher than the first temperature, the first non-conductive ball comprising the step of: The second non-conductive ball has a melting point higher than the melting point of the low-melting solder ball, and the second non-conductive ball has a melting point higher than the melting point of the low-melting solder ball and is larger than the diameter of the first non-conductive ball. Has a small diameter That.

  In addition, a flip chip bonding method according to still another aspect of the present invention includes a conductive material including a low melting point solder ball, a polymer resin, and a non-conductive ball having a melting point higher than the melting point of the low melting point solder ball. Preparing an adhesive on the substrate, aligning the electrodes of the semiconductor chip and the electrodes of the substrate, and the semiconductor chip and the semiconductor chip at a predetermined first temperature higher than the melting point of the low melting point solder ball Applying a predetermined pressure to the substrate, and applying the predetermined pressure between the semiconductor chip and the substrate at a second temperature higher than the first temperature.

  The present invention reduces the cost by simply adjusting the pressure without a separate elaborate control technique by including a non-conductive ball in the conductive adhesive to adjust the distance between the semiconductor chip and the substrate. Thus, the flip chip bonding process can be carried out, whereby the process time can be shortened and the yield of the product can be increased.

  Further, the present invention can improve the heat generation characteristics of a semiconductor by using a conductive adhesive having excellent thermal conductivity as an isotropic conductive adhesive in a bonding process between semiconductor wafers.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a diagram illustrating a configuration of a conductive adhesive according to an embodiment of the present invention. Referring to FIG. 1, the conductive adhesive 110 includes a low melting point solder ball 111 and a polymer resin 112, and further includes a first nonconductive ball 113 and a second nonconductive ball 114. In one embodiment, the low melting point solder ball 111 may be made of Sn / Bi or the like and have a melting point of about 140 ° C. Further, the polymer resin 112 can be made of a polymer insulating resin such as a thermosetting phenol resin or a melanin resin.

  The first non-conductive ball 113 and the second non-conductive ball 114 serve as a stand-off for maintaining a constant distance between the electrode of the semiconductor chip and the electrode of the substrate during fusion and wetting of the low melting point solder balls 111. For this purpose, the low melting point solder ball 111 is made of a material that is not melted even at a temperature higher than the melting point of the low melting point solder ball 111, that is, a material having a melting point higher than that of the low melting point solder ball 111. In the bonding process, the first non-conductive ball 113 has a diameter larger than the diameter of the second non-conductive ball 114 in order to adjust the interval in two stages. In one embodiment, the first non-conductive ball 113 may be made of a polymer such as PMMA (Polymethyl methacrylate), polycarbonate, Polystyrene, and the second non-conductive ball 114 is The first non-conductive ball 113 may be made of the same material as the first non-conductive ball 113 or a glass type substance having a hardness greater than that of the first non-conductive ball 113.

  On the other hand, since the low melting point solder ball 111 contained in the conductive adhesive 110 is excellent not only in electrical conductivity but also in thermal conductivity, the conductive adhesive 110 is used for the semiconductor wafer by utilizing such points. It can also be used in the bonding process between. In other words, the conductive adhesive 110 can be used as an anisotropic conductive adhesive for electrically connecting the electrode of the semiconductor chip and the electrode of the substrate in the flip chip bonding process. In the process, it can also be used as an isotropic conductive adhesive that facilitates heat conduction between semiconductor wafers and improves the heat generation characteristics of the semiconductor. At this time, the first non-conductive balls 113 and the second non-conductive balls 114 serve to maintain a distance so that the low melting point solder balls 111 can be sufficiently fused and wetted between the semiconductor wafers.

  2a to 2c are diagrams for explaining a flip chip bonding method according to a first embodiment of the present invention, and FIG. 2d is a diagram illustrating temperature according to time in the flip chip bonding method according to the first embodiment of the present invention. It is a graph which shows the change of pressure.

  Referring to FIG. 2a, the conductive adhesive 210 may be formed in a film or pastry form by mixing a low melting point solder ball 211, a first non-conductive ball 213, and a second non-conductive ball 214 with a polymer resin 212. And is located between the semiconductor chip 220 to be bonded and the substrate 230.

  After aligning the semiconductor chip 220 and the substrate 230 using the flip chip bonding equipment, if a pressure is applied between the semiconductor chip 220 and the substrate 230, the first non-conductive material having the largest diameter inside the conductive adhesive 210 is formed. Pressure is applied to the ball 213. Accordingly, the interval between the semiconductor chip 220 and the substrate 230 is determined by the elasticity of the first non-conductive ball 213 and the pressure between the semiconductor chip 220 and the substrate 230.

  At this time, since the diameter of the second non-conductive ball 214 is smaller than the diameter of the first non-conductive ball 213, the second non-conductive ball 214 has not been deformed until the first non-conductive ball 213 is deformed. The pressure applied between the semiconductor chip 220 and the substrate 230 is not affected.

  Referring to FIGS. 2b and 2d, if the temperature increases and passes the first temperature which is the melting point of the low melting point solder ball 211 at time 1, the low melting point solder balls 211 are fused together, and the semiconductor chip 220 and the substrate A concave lens shape is formed between 230 electrodes 221 and 231. In one embodiment, when the low melting point solder ball 211 is made of Sn / Bi, the first temperature may be 139 ° C. to 141 ° C.

  At this time, since the polymer resin 212 maintains a low viscosity of several hundred cps, it does not affect the fusion and wetting of the low melting point solder balls 211. Further, since the first non-conductive ball 213 and the second non-conductive ball 214 are made of a polymer having very poor wettability with respect to the low melting point solder ball 211, the first non-conductive ball 213 and the second non-conductive ball 213 The non-conductive balls 214 also do not affect the fusion and wetting of the low melting point solder balls 211.

Thereafter, the temperature and the pressure increase, reach the first pressure and the second temperature at time 2, and maintain the first pressure and the second temperature for a predetermined time (time 2 to time 3). At this time, the first pressure is lower than the deformation pressure of the first non-conductive ball 213. Here, the deformation pressure refers to a pressure at which deformation of the structure starts to occur when pressure is applied to the structure having a certain form. In one embodiment, the first pressure is 100 g / cm ^{2 to} 300 g / cm ² and the second temperature is 155 ° C. to 165 ° C.

  The distance between the semiconductor chip 220 and the substrate 230 is determined by the elasticity and the first pressure of the first non-conductive ball 213 serving as a standoff, and such a distance is sufficient for the fusion of the low melting point solder balls 211 and It is maintained for a predetermined time (time 2 to time 3) for weighting. In one embodiment, for sufficient fusion and wetting of the low melting solder ball 211, the first pressure and the second temperature are maintained for approximately 70 seconds.

Referring to FIGS. 2 c and 2 d, after the elapse of time 3, the pressure is increased and the second pressure is reached at time 4. At this time, the second pressure is higher than the deformation pressure of the first non-conductive ball 213 and lower than the deformation pressure of the second non-conductive ball 214. In one example, the second pressure is between 300 g / cm ^{2 and} 600 g / cm ² .

  When the second pressure is applied, the distance between the semiconductor chip 220 and the electrodes 221 and 231 formed on the surface of the substrate 230 is reduced, and the second pressure is applied to the first non-conductive ball 213 and the second non-conductive ball. The distance between the semiconductor chip 220 and the substrate 230 is determined. The low-melting-point solder balls 211 fused and wetted at intervals determined by the first pressure form a convex lens shape by narrowing the intervals by the second pressure. Thereby, the junction area of the low melting point solder ball 211 and the electrodes 221 and 231 can be maximized.

  At the same time, the temperature increases as the pressure increases and reaches the third temperature at time 4. Here, the third temperature is a temperature at which the curing reaction of the polymer resin 212 starts, that is, a temperature higher than the thermosetting temperature of the polymer resin 212. If the temperature is decreased after maintaining the third temperature for a predetermined time (time 4 to time 5), the polymer resin 212 is cured by about 70% or more, and is about 90% of the fully cured state. Shows physical properties. In one embodiment, the third temperature is between 179 ° C. and 181 ° C. When the degree of curing of the polymer resin 212 is required to be 95% or more, an additional curing step of applying atmospheric pressure or second pressure at the third temperature can be performed.

  In order to reduce the complexity of the process using two stages of pressure, a second embodiment using a conductive adhesive that does not include the first non-conductive ball is described below with reference to FIGS. 3a-3c. To do.

  FIGS. 3a and 3b are diagrams for explaining a flip chip bonding method according to a second embodiment of the present invention, and FIG. 3c illustrates a temperature according to time in the flip chip bonding method according to the second embodiment of the present invention. It is a graph which shows the change of pressure.

  Referring to FIG. 3a, a conductive adhesive 310 is a semiconductor chip 320 that is manufactured in a film or pastry form by mixing a low melting point solder ball 311 and a second non-conductive ball 313 with a polymer resin 312 and is bonded. And the substrate 330.

  After aligning the semiconductor chip 320 and the substrate 330 using the flip chip bonding equipment, if pressure is applied between the semiconductor chip 320 and the substrate 330, pressure is applied to the second non-conductive ball 313. The distance between the semiconductor chip 320 and the substrate 330 is determined by the elasticity of the second non-conductive ball 313 and the pressure between the semiconductor chip 320 and the substrate 330.

Referring to FIGS. 3b and 3c, the viscosity of the polymer resin 312 decreases to several hundred cps as the temperature increases while maintaining the second pressure, and the temperature of the low melting point solder ball 311 decreases as time 1 elapses. Thus, the low melting point solder ball 311 changes from the solid state to the liquid state. Here, the second pressure is a pressure lower than the deformation pressure of the second non-conductive ball 313, similarly to the second pressure of the first embodiment. In one example, the second pressure is between 300 g / cm ^{2 and} 600 g / cm ² .

  At time 2, the temperature reaches the second temperature and is maintained for a predetermined time (time 2 to time 3). As a result, the low melting point solder balls 311 are fused together and formed in a convex lens shape between the semiconductor chip 320 and the electrodes 321 and 331 of the substrate 330. In one embodiment, the second temperature is between 155 ° C and 165 ° C.

  Thereafter, the temperature further increases and reaches the third temperature at time 4. Here, the third temperature is higher than the thermosetting temperature of the polymer resin 312 as in the third temperature of the first embodiment. If the temperature is decreased after maintaining the third temperature for a predetermined time (time 4 to time 5), the polymer resin 312 is cured by approximately 70% or more, and is about 90% of the fully cured state. Shows physical properties. In one embodiment, the third temperature is between 179 ° C. and 181 ° C. When the degree of curing of the polymer resin 312 is required to be 95% or more, an additional curing step of applying atmospheric pressure or second pressure at the third temperature can be performed.

  On the other hand, when the conductive adhesive according to an embodiment of the present invention is used as an isotropic conductive adhesive in a semiconductor wafer bonding process, the low melting point solder ball is sufficiently fused and wetted between the semiconductor wafers. Thus, the interval between the semiconductor wafers needs to be maintained during a predetermined time. Therefore, the remaining bonding process except the step of aligning the semiconductor chip and the substrate in the bonding method described with reference to FIGS. 2a to 3c can be applied to the semiconductor wafer bonding process.

  The present invention described above can be variously replaced, modified, and changed without departing from the technical idea of the present invention as long as it has ordinary knowledge in the technical field to which the present invention belongs. Therefore, the present invention is not limited to the above-described embodiment and attached drawings.

It is a figure which shows the structure of the electrically conductive adhesive which concerns on one Example of this invention. It is a figure for demonstrating the flip-chip bonding method based on 1st Example of this invention. It is a figure for demonstrating the flip-chip bonding method based on 1st Example of this invention. It is a figure for demonstrating the flip-chip bonding method based on 1st Example of this invention. 4 is a graph showing changes in temperature and pressure with time in the flip chip bonding method according to the first embodiment of the present invention. It is a figure for demonstrating the flip-chip bonding method based on 2nd Example of this invention. It is a figure for demonstrating the flip-chip bonding method based on 2nd Example of this invention. 6 is a graph showing changes in temperature and pressure with time in a flip chip bonding method according to a second embodiment of the present invention.

Explanation of symbols

111 Low melting point solder ball 112 Polymer resin 113 First non-conductive ball 114 Second non-conductive ball

Claims (10)

A thermosetting polymer resin selected from phenolic resins or melanin resins;
Solder balls that are dispersed in the polymer resin and have a first temperature as a melting point;
Dispersed in the polymer resin, including a non-conductive ball having a melting point higher than the first temperature,
The non-conductive ball includes a first non-conductive ball and a second non-conductive ball having a diameter smaller than the diameter of the first non-conductive ball, and the hardness of the second non-conductive ball is A conductive adhesive having a hardness higher than that of the first non-conductive ball. The first non-conductive ball is made of a polymer material,
The conductive adhesive according to claim 1, wherein the second non-conductive ball is made of the same material as the first non-conductive ball or glass.   The conductive adhesive according to claim 2, wherein the first non-conductive ball is made of PMMA (Polymethyl methacrylate), Polycarbonate, Polystyrene. In a flip chip bonding method for bonding a semiconductor chip to a substrate,
(A) a solder ball having a first temperature as a melting point, a polymer resin selected from a phenol resin or a melanin resin, a first non-conductive ball and a second non-conductive ball having a melting point higher than the first temperature Providing on the substrate a conductive adhesive comprising:
(B) aligning the electrodes of the semiconductor chip and the electrodes of the substrate;
(C) applying a first pressure between the semiconductor chip and the substrate at a second temperature higher than the first temperature;
(D) applying a second pressure higher than the first pressure between the semiconductor chip and the substrate at a third temperature higher than the second temperature;
The flip chip bonding method, wherein the second non-conductive ball has a diameter smaller than that of the first non-conductive ball.   5. The flip chip bonding method according to claim 4, wherein the hardness of the second non-conductive ball is greater than the hardness of the first non-conductive ball.   5. The flip chip bonding method according to claim 4, wherein the first pressure is less than a deformation pressure of the first non-conductive ball.   5. The flip-chip bonding method according to claim 4, wherein the second pressure is equal to or higher than a deformation pressure of the first non-conductive ball and lower than a deformation pressure of the second non-conductive ball.   The flip chip bonding method according to claim 4, wherein the third temperature is equal to or higher than a thermosetting temperature of the polymer resin.   5. The flip chip bonding method according to claim 4, wherein the second temperature is 155 ° C. to 165 ° C., and the third temperature is 179 ° C. to 181 ° C. 6. 5. The flip chip bonding method according to claim 4, wherein the first pressure is 100 g / cm ^{2 to} 300 g / cm ² , and the second pressure is 300 g / cm ^{2 to} 600 g / cm ^2. .

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