JP2016140870A - Method for forming a solder bump - Google Patents
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Abstract
Description
本発明は、ワーク上に形成されるはんだバンプの形成方法に関する。 The present invention relates to a method for forming solder bumps formed on a workpiece.
従来より、電子機器や半導体の製造には、複数の被接合部、例えば電子部品と基板やシリコンウエハといったワークとを接合した接合構造体が用いられている。このような接合構造体は複数の被接合部間にはんだ層が形成されており、このはんだ層を介して各被接合部が接合されている。そしてこのような接合構造体を製造する際にワーク上にはんだバンプを形成し、このはんだバンプを介して複数の被接合部を接合する方法が用いられている。 Conventionally, in the manufacture of electronic devices and semiconductors, a joined structure in which a plurality of joined parts, for example, electronic components and a workpiece such as a substrate or a silicon wafer are joined is used. In such a bonded structure, a solder layer is formed between a plurality of bonded portions, and the bonded portions are bonded via the solder layer. And when manufacturing such a joining structure, a solder bump is formed on a work and a method of joining a plurality of joined parts via this solder bump is used.
このようなはんだバンプの形成に際して、ソルダペースト等のはんだ材料の濡れ性が不十分な場合、形成されるはんだバンプの中にボイド（気泡）が発生することがある。このようなボイドは被接合部間の接合性の低下や放熱性の低下を生じさせ、電子機器や半導体の信頼性の低下に繋がる。 When forming such solder bumps, if the wettability of solder material such as solder paste is insufficient, voids (bubbles) may be generated in the formed solder bumps. Such voids cause a decrease in bondability between the bonded portions and a decrease in heat dissipation, leading to a decrease in the reliability of electronic devices and semiconductors.
このようなボイドの発生を抑制する方法として、例えば水素ガス等の還元性の高い雰囲気下で加熱してはんだ材料の濡れ性を向上させる方法や、はんだ材料を介した被接合部を加熱してはんだ合金を溶融させ、その後これを収納した容器内を真空雰囲気下とすることで、はんだ合金内の空気を脱泡する方法が用いられてきた。 As a method for suppressing the generation of such voids, for example, a method of improving the wettability of the solder material by heating in a highly reducing atmosphere such as hydrogen gas, or heating a bonded portion via the solder material. A method has been used in which the solder alloy is melted, and then the air in the solder alloy is degassed by placing the container containing the solder alloy in a vacuum atmosphere.
また、はんだを溶融させた状態で減圧と加圧を複数回繰り返すことによりボイドの大きさを狭小化する方法（特許文献１）、一旦大気圧より低い第１圧力に減圧した後にハンダを溶融させ、昇温したまま第１圧力より高く大気圧を超えない第２圧力まで昇圧し、昇温したまま第１圧力より高く第２圧力より低い第３圧力まで減圧し、その後大気圧を超えない圧力に戻した後にハンダの融点以下に降温させる方法（特許文献２）、ほぼ大気圧下において半田を溶融させた後にこれを減圧し、その後にほぼ大気圧に戻す圧力変化過程を複数回繰り返す方法（特許文献３）等が開示されている。 In addition, a method of narrowing the size of the void by repeating the pressure reduction and pressurization a plurality of times while the solder is melted (Patent Document 1), once the pressure is reduced to the first pressure lower than the atmospheric pressure, the solder is melted The pressure is increased to a second pressure that is higher than the first pressure and does not exceed atmospheric pressure while the temperature is increased, and is reduced to a third pressure that is higher than the first pressure and lower than the second pressure while the temperature is increased, and then the pressure that does not exceed atmospheric pressure (Patent Document 2), after melting the solder at approximately atmospheric pressure, depressurizing the solder, and then repeating the pressure changing process to return to approximately atmospheric pressure a plurality of times (Patent Document 2) Patent Document 3) and the like are disclosed.
特許文献１および特許文献３に開示される方法の場合、減圧と加圧を複数回行う過程で脱泡の際にボイドが破裂したり、はんだ（半田）の濡れ性が悪化して十分にボイドを脱泡できなくなる虞がある。
また特許文献２に開示される方法の場合、減圧状態下ではんだ合金の溶融温度以上に昇温するため、ソルダペーストを用いた場合にはこれに含まれるフラックスが揮発し易くなり、はんだ合金の溶融性が低下する虞がある。
In the case of the methods disclosed in
Further, in the case of the method disclosed in
本発明は、効率よくはんだバンプ中のボイドを低減することのできるはんだバンプの形成方法を提供することをその目的とする。 An object of the present invention is to provide a method for forming a solder bump that can efficiently reduce voids in the solder bump.
（１）本発明のはんだバンプの形成方法は、フラックスおよびはんだ合金からなるソルダペーストをワーク上の所定の位置に印刷する工程と、前記ワークを大気圧の近傍である第１の圧力下にて加熱する工程と、前記ワークを加熱する加熱温度が前記はんだ合金の液相温度近傍以上になった以降に前記ワーク周囲の圧力を前記第１の圧力よりも低い第２の圧力まで減圧する工程と、前記加熱温度が前記はんだ合金の液相温度以上の状態で前記ワーク周囲の圧力を前記第２の圧力よりも高い第３の圧力まで加圧する工程と、前記加熱温度が前記はんだ合金の液相温度以上の状態で前記ワーク周囲の圧力を前記第１の圧力まで加圧する工程と、前記ワーク周囲の圧力が前記第１の圧力に到達した以降に前記加熱温度を前記はんだ合金の液相温度以下にして前記ワーク上にはんだバンプを形成する工程とを含み、前記第２の圧力まで減圧する工程と前記第３の圧力まで加圧する工程とを複数回行うことをその特徴とする。 (1) The method for forming a solder bump of the present invention includes a step of printing a solder paste made of a flux and a solder alloy at a predetermined position on a workpiece, and the workpiece under a first pressure that is near atmospheric pressure. A step of heating, and a step of reducing the pressure around the workpiece to a second pressure lower than the first pressure after the heating temperature for heating the workpiece becomes near the liquidus temperature of the solder alloy. Pressurizing the pressure around the workpiece to a third pressure higher than the second pressure in a state where the heating temperature is equal to or higher than the liquid phase temperature of the solder alloy, and the heating temperature is a liquid phase of the solder alloy. Pressurizing the pressure around the workpiece to the first pressure in a state of temperature or higher, and after the pressure around the workpiece reaches the first pressure, the heating temperature is less than the liquid phase temperature of the solder alloy. And forming a solder bump on the workpiece in the, and its characterized in that said second plurality of times and a step of pressurizing to said third pressure and a step of pressure reduction to a pressure.
（２）上記（１）に記載の構成にあって、前記第２の圧力は、５０Ｐａから１００Ｐａであることをその特徴とする。 (2) In the configuration described in (1) above, the second pressure is 50 Pa to 100 Pa.
（３）上記（１）または（２）に記載の構成にあって、前記第３の圧力まで加圧する工程において、前記ワーク周囲の圧力が前記第３の圧力に到達した時点の前記加熱温度は前記はんだ合金の液相温度より１０℃以上であることをその特徴とする。 (3) In the configuration described in (1) or (2) above, in the step of pressurizing to the third pressure, the heating temperature at the time when the pressure around the workpiece reaches the third pressure is It is characterized by being 10 ° C. or higher than the liquidus temperature of the solder alloy.
（４）上記（１）から（３）のいずれか１つに記載の構成にあって、前記第３の圧力は、１０，０００Ｐａから５０，０００Ｐａであることをその特徴とする。 (4) In the configuration described in any one of (1) to (3) above, the third pressure is 10,000 Pa to 50,000 Pa.
（５）上記（１）から（３）のいずれか１つに記載の構成にあって、前記第２の圧力まで減圧する工程と前記第３の圧力まで加圧する工程とを２回から４回行うことをその特徴とする。 (5) In the configuration according to any one of (1) to (3) above, the step of reducing the pressure to the second pressure and the step of pressurizing to the third pressure are performed twice to four times. It is characterized by what it does.
（６）上記（４）に記載の構成にあって、前記第２の圧力まで減圧する工程と前記第３の圧力まで加圧する工程とを２回から６回行うことをその特徴とする。 (6) In the configuration described in (4) above, the step of reducing the pressure to the second pressure and the step of pressurizing to the third pressure are performed twice to six times.
（７）上記（１）から（６）のいずれか１つに記載の構成にあって、前記第１の圧力から第２の圧力まで減圧してからこれを前記第３の圧力まで加圧するまでにかかる１回のサイクルタイムは、１０秒間から４０秒間であることをその特徴とする。 (7) In the configuration according to any one of (1) to (6) above, from depressurization from the first pressure to the second pressure and then pressurizing it to the third pressure One cycle time for the above is characterized in that it is 10 seconds to 40 seconds.
上記構成により、本発明に係るはんだバンプの形成方法は、効率よくはんだバンプ中のボイドを脱泡することができる。 With the above configuration, the solder bump forming method according to the present invention can efficiently degas voids in the solder bump.
以下、本発明のはんだバンプの形成方法の一実施形態について詳細に説明する。なお、本発明が当該実施形態に限定されないのはもとよりである。 Hereinafter, an embodiment of the method for forming solder bumps of the present invention will be described in detail. Of course, the present invention is not limited to this embodiment.
先ず、図１を用いて本実施形態の形成方法により形成されるはんだバンプを説明する。本実施形態においてはワークとして基板１１を使用しているが、プリント基板、シリコンウエハ等、電子部品の搭載、実装に用いられる基材であればこれらに限らずワークとして使用することができる。図１に示すように、はんだバンプ１０は、基板１１上に形成される。
First, solder bumps formed by the forming method of this embodiment will be described with reference to FIG. In the present embodiment, the substrate 11 is used as a workpiece. However, the substrate 11 can be used as a workpiece as long as it is a substrate used for mounting and mounting electronic components such as a printed board and a silicon wafer. As shown in FIG. 1, the
次に本実施形態の形成方法では、先ず基板１１上の所定の位置にはんだ合金とフラックスとを混合したソルダペーストを塗布する。このようなフラックスとしては、例えばベース樹脂と溶剤と活性剤とを含むものが挙げられる。
また前記ベース樹脂としては例えばロジン系樹脂、アクリル系樹脂等が、前記活性剤としては例えば有機酸、アミン類又はこれらのハロゲン化物等が挙げられる。またこれらに酸化防止剤、チキソ剤を添加したフラックスも好ましく用いられる。
Next, in the forming method of this embodiment, first, a solder paste in which a solder alloy and a flux are mixed is applied to a predetermined position on the substrate 11. Examples of such flux include those containing a base resin, a solvent, and an activator.
Examples of the base resin include rosin resins and acrylic resins, and examples of the activator include organic acids, amines, and halides thereof. Moreover, the flux which added antioxidant and the thixotropic agent to these is also used preferably.
このようなフラックスを用いることで、はんだ合金の濡れ性を向上し、形成するはんだバンプのボイド発生を抑制することができる。 By using such a flux, the wettability of the solder alloy can be improved and the generation of voids in the solder bumps to be formed can be suppressed.
また前記はんだ合金の組成も特に限定されないが、環境の観点から鉛フリーはんだであることが好ましい。なお、本実施形態においてはＳｎ−３Ａｇ−０．５Ｃｕ組成の鉛フリーはんだ合金を使用する。 The composition of the solder alloy is not particularly limited, but is preferably lead-free solder from the viewpoint of environment. In this embodiment, a lead-free solder alloy having a Sn-3Ag-0.5Cu composition is used.
次いで、ソルダペーストを塗布した基板１１を例えば真空リフローはんだ付け装置に備え付けられた真空チャンバに収容する。
基板１１を収容した前記真空チャンバ内は第１の圧力（Ｐ１）となるよう調整される。なおこの調整にあたっては、例えば、一旦室温にて大気圧状態から真空引きを行い前記真空チャンバ内を真空状態とした後、窒素等の不活性ガス、水素等の還元性ガスを供給して第１の圧力（Ｐ１）とすることが好ましい。また第１の圧力（Ｐ１）は、大気圧近傍であることが好ましい。
Next, the substrate 11 to which the solder paste is applied is accommodated in, for example, a vacuum chamber provided in a vacuum reflow soldering apparatus.
The inside of the vacuum chamber containing the substrate 11 is adjusted to be the first pressure (P1). In this adjustment, for example, after first evacuating from the atmospheric pressure state at room temperature to make the inside of the vacuum chamber into a vacuum state, an inert gas such as nitrogen or a reducing gas such as hydrogen is supplied. The pressure (P1) is preferable. The first pressure (P1) is preferably near atmospheric pressure.
そして前記真空チャンバ内を第１の圧力（Ｐ１）下としたまま前記真空チャンバ内を加熱することで基板１１を加熱する。本実施形態における温度プロファイルおよび前記容器内（＝基板１１周囲）の圧力の変化を図２に示す。なお図２に示すように一定時間の予熱温度（図２では１５０℃）を保っても良い。
また、本実施形態においては第１の圧力（Ｐ１）下での加熱を前記真空チャンバ内で行ったが、例えば第１の圧力（Ｐ１）下での加熱はリフロー装置の加熱ゾーンにて行い、その後に基板１１を前記真空チャンバ内に収容するようにしても良い。
Then, the substrate 11 is heated by heating the inside of the vacuum chamber while keeping the inside of the vacuum chamber under the first pressure (P1). FIG. 2 shows changes in the temperature profile and the pressure in the container (= around the substrate 11) in the present embodiment. In addition, as shown in FIG. 2, you may keep the preheating temperature (150 degreeC in FIG. 2) for a fixed time.
In the present embodiment, the heating under the first pressure (P1) is performed in the vacuum chamber. For example, the heating under the first pressure (P1) is performed in the heating zone of the reflow device, Thereafter, the substrate 11 may be accommodated in the vacuum chamber.
基板１１への加熱温度が前記はんだ合金の液相温度近傍以上となった以降、前記真空チャンバ内の圧力を第１の圧力（Ｐ１）よりも低い第２の圧力（Ｐ２）まで減圧する。
本実施形態では、図２に示す温度プロファイルがはんだ合金の液相温度近傍以上となった以降、即ち前記真空チャンバ内の温度（Ｄ）が前記はんだ合金の液相温度である２２０℃（Ｄ１）になった際に、前記真空チャンバ内の圧力を第１の圧力（Ｐ１）よりも低い第２の圧力（Ｐ２）まで減圧する。減圧の方法としては、例えば前記真空チャンバに備え付けたポンプ（図示せず）を用いて、前記真空チャンバから気体を排気する方法が挙げられる。なお、特に前記真空チャンバ内が液相温度以上となった以降に前記真空チャンバ内の圧力を第２の圧力（Ｐ２）まで減圧することが好ましい。
After the heating temperature to the substrate 11 becomes equal to or higher than the liquid phase temperature of the solder alloy, the pressure in the vacuum chamber is reduced to a second pressure (P2) lower than the first pressure (P1).
In the present embodiment, after the temperature profile shown in FIG. 2 becomes equal to or higher than the liquid phase temperature of the solder alloy, that is, the temperature (D) in the vacuum chamber is 220 ° C. (D1), which is the liquid phase temperature of the solder alloy. The pressure in the vacuum chamber is reduced to a second pressure (P2) lower than the first pressure (P1). As a method for reducing the pressure, for example, a method of exhausting gas from the vacuum chamber using a pump (not shown) provided in the vacuum chamber can be mentioned. In particular, it is preferable that the pressure in the vacuum chamber is reduced to the second pressure (P2) after the inside of the vacuum chamber becomes equal to or higher than the liquid phase temperature.
このように、第２の圧力（Ｐ２）への減圧のタイミングを前記真空チャンバ内の温度がその液相温度近傍（本実施形態の場合は液相温度である２２０℃（Ｄ１））になった際に行うことにより、前記ソルダペーストに用いられるフラックス量の減少による前記はんだ合金の溶融性の低下を防ぐことができる。即ち、前記はんだ合金が溶融する前から長時間、前記真空チャンバ内を減圧状態としておくと前記フラックス量が減少し易くなり、前記はんだ合金の溶融性に影響を及ぼす虞がある。
なお本実施形態において液相温度近傍とは、前記はんだ合金の５割以上が溶融する温度を言う。
As described above, the timing of pressure reduction to the second pressure (P2) is such that the temperature in the vacuum chamber is close to the liquidus temperature (in this embodiment, the liquidus temperature is 220 ° C. (D1)) By doing so, it is possible to prevent a decrease in the meltability of the solder alloy due to a decrease in the amount of flux used in the solder paste. That is, if the vacuum chamber is kept in a reduced pressure state for a long time before the solder alloy is melted, the amount of flux tends to decrease, which may affect the meltability of the solder alloy.
In the present embodiment, the vicinity of the liquidus temperature refers to a temperature at which 50% or more of the solder alloy melts.
また本実施形態において、第２の圧力（Ｐ２）は、５０Ｐａから１００Ｐａであることが好ましい。この範囲は、はんだバンプが形成された基板（ワーク）の用途によって適宜選定することができる。 In the present embodiment, the second pressure (P2) is preferably 50 Pa to 100 Pa. This range can be appropriately selected depending on the use of the substrate (workpiece) on which the solder bumps are formed.
第２の圧力（Ｐ２）の真空度が高ければ高いほど前記はんだ合金内に含まれているボイドの膨張サイズが大きくなり、またその後の加圧時の圧力の差が大きくなるため、前記はんだ合金からのボイド排出効果は高まる。しかし本実施形態の場合、第２の圧力（Ｐ２）の真空度が５０Ｐａ以上であっても効率よくボイドの低減効果を発揮することができる。 The higher the degree of vacuum of the second pressure (P2), the larger the expansion size of the voids contained in the solder alloy, and the greater the difference in pressure during subsequent pressurization. The void discharge effect from is increased. However, in the case of this embodiment, even if the degree of vacuum of the second pressure (P2) is 50 Pa or more, the effect of reducing voids can be efficiently exhibited.
次に前記真空チャンバ内の圧力を第２の圧力（Ｐ２）よりも高い第３の圧力（Ｐ３）まで加圧する。加圧の方法としては、例えば前記真空チャンバ内に窒素等の不活性ガス、水素等の還元性ガスを供給して第３の圧力（Ｐ３）まで調整することが好ましい。
ここで第３の圧力（Ｐ３）に到達した時点の前記真空チャンバ内の温度（Ｄ２）は、前記はんだ合金の液相温度以上であることが好ましい。前記はんだ合金が凝固し始めた状態で第３の圧力（Ｐ３）まで加圧すると、ボイドが膨張した状態で前記はんだバンプに閉じ込められる虞がある。
Next, the pressure in the vacuum chamber is increased to a third pressure (P3) higher than the second pressure (P2). As a method of pressurization, for example, it is preferable to adjust the pressure to the third pressure (P3) by supplying an inert gas such as nitrogen or a reducing gas such as hydrogen into the vacuum chamber.
Here, the temperature (D2) in the vacuum chamber when the third pressure (P3) is reached is preferably equal to or higher than the liquidus temperature of the solder alloy. When the solder alloy starts to solidify and is pressurized to the third pressure (P3), the voids may be confined in the solder bumps in an expanded state.
なお、前記真空チャンバ内に窒素等のガスを供給する際、これらガスの温度との差異により、一旦前記真空チャンバ内の温度が下がることがある。この場合において、前記真空チャンバ内の温度（Ｄ２）と液相温度との差が小さい場合、この内部温度の低下により前記はんだ合金の一部に固相が発生して前記はんだ合金内のボイド排出効果を妨げ、形成したはんだバンプにボイドが膨張した状態で閉じ込められる虞がある。特に固相温度と液相温度の範囲が狭いはんだ合金を使用する場合、このような現象が起きやすくなる。前記真空チャンバ内の温度（Ｄ２）を前記はんだ合金の液相温度以上、特に液相温度より１０℃以上とすることで、この現象を抑制することができる。 When a gas such as nitrogen is supplied into the vacuum chamber, the temperature in the vacuum chamber may be temporarily lowered due to a difference with the temperature of these gases. In this case, when the difference between the temperature (D2) in the vacuum chamber and the liquid phase temperature is small, a solid phase is generated in a part of the solder alloy due to a decrease in the internal temperature, and voids in the solder alloy are discharged. The effect may be hindered, and the void may be trapped in the formed solder bump. Such a phenomenon is likely to occur particularly when a solder alloy having a narrow range between the solid phase temperature and the liquid phase temperature is used. This phenomenon can be suppressed by setting the temperature (D2) in the vacuum chamber to be equal to or higher than the liquid phase temperature of the solder alloy, particularly 10 ° C. higher than the liquid phase temperature.
また、第３の圧力（Ｐ３）は、１０，０００Ｐａから５０，０００Ｐａであることが好ましい。この第３の圧力（Ｐ３）をこの範囲内とすることにより減圧と加圧のサイクルタイムを短縮することができ、短時間で複数回の減圧と加圧が可能になるため、効率よくはんだバンプのボイド低減を実現できる。またこの場合、前記ソルダペーストに含まれるフラックス量の減少およびこれによる前記はんだ合金表面の再酸化を抑制することができる。
一般的に、前記真空チャンバ内を真空圧に減圧すれば前記はんだ合金内に含まれているボイドの膨張サイズは大きくなり外に排出され易く、またその後に前記真空チャンバ内を大気圧まで加圧すれば前記ボイドが収縮する事ではんだに流動性を与え脱泡効果は向上する。一方、この減圧時と加圧時の圧力の差が大きいと脱泡時にボイドと共に溶融した前記はんだ合金が飛散する現象が起きる可能性がある。しかし第３の圧力（Ｐ３）を前記範囲内とした場合、このような飛散現象を抑制することができる。なお、後述のように本実施形態においては減圧と加圧を複数回繰り返すため、前記はんだ合金内のボイドを効率よく低減することができ、且つ、第３の圧力（Ｐ３）を前記範囲内とした場合、繰り返しによる前記飛散現象を抑制することもできる。
The third pressure (P3) is preferably 10,000 Pa to 50,000 Pa. By setting the third pressure (P3) within this range, the cycle time of pressure reduction and pressurization can be shortened, and multiple times of pressure reduction and pressurization are possible in a short time. Can be reduced. In this case, it is possible to suppress a decrease in the amount of flux contained in the solder paste and reoxidation of the solder alloy surface due to this.
In general, if the inside of the vacuum chamber is reduced to a vacuum pressure, the expansion size of the voids contained in the solder alloy increases and is easily discharged to the outside, and then the inside of the vacuum chamber is pressurized to atmospheric pressure. In this case, the voids shrink, thereby giving the solder fluidity and improving the defoaming effect. On the other hand, if the difference between the pressure at the time of depressurization and the pressure at the time of pressurization is large, there is a possibility that the solder alloy melted together with the void at the time of defoaming is scattered. However, when the third pressure (P3) is within the above range, such a scattering phenomenon can be suppressed. As will be described later, in this embodiment, since the pressure reduction and the pressurization are repeated a plurality of times, voids in the solder alloy can be efficiently reduced, and the third pressure (P3) is within the above range. In this case, the scattering phenomenon due to repetition can be suppressed.
この第１の圧力（Ｐ１）から第２の圧力（Ｐ２）への減圧、および第２の圧力（Ｐ２）から第３の圧力（Ｐ３）への加圧を１サイクルとした場合の１回のサイクルタイムは１０秒間から４０秒間であることが好ましい。１回のサイクルタイムをこの時間内とすることで、フラックス量の減少およびこれによる前記はんだ合金表面の再酸化を抑制することができる。一方、１回のサイクルタイムが４０秒間より長くなると、前記ソルダペーストに含まれるフラックス量が減少し易くなり、前記はんだ合金からボイドを排除し難くなる虞がある。 When the pressure reduction from the first pressure (P1) to the second pressure (P2) and the pressurization from the second pressure (P2) to the third pressure (P3) are one cycle, The cycle time is preferably 10 seconds to 40 seconds. By setting one cycle time within this time, it is possible to suppress a decrease in the amount of flux and reoxidation of the solder alloy surface due to this. On the other hand, if the cycle time of one time is longer than 40 seconds, the amount of flux contained in the solder paste is likely to decrease, and it may be difficult to eliminate voids from the solder alloy.
また第１の圧力（Ｐ１）から第２の圧力（Ｐ２）までの減圧工程、および第２の圧力（Ｐ２）から第３の圧力（Ｐ３）までの加圧工程は複数回行われる。このように減圧と加圧を複数回繰り返すことにより溶融した前記はんだ合金内のボイドの脱泡を促し、形成したはんだバンプ内に残存するボイドを低減することが可能となる。 The depressurization step from the first pressure (P1) to the second pressure (P2) and the pressurization step from the second pressure (P2) to the third pressure (P3) are performed a plurality of times. In this way, by repeating the depressurization and pressurization a plurality of times, it is possible to promote the defoaming of the voids in the molten solder alloy, and it is possible to reduce the voids remaining in the formed solder bumps.
なお、この減圧工程と加圧工程の回数は２回から４回であることが好ましい。この減圧工程と加圧工程の回数は多い方が好ましいものの、回数を増やすために前記真空チャンバ内の加熱時間、特にピークの加熱時間が延びてしまうと、前記ソルダペーストに含まれるフラックス量が減少し、前記はんだ合金の表面が再酸化してしまう虞がある。
なお、前述のように第３の圧力（Ｐ３）を１０，０００Ｐａから５０，０００Ｐａの範囲内とした場合、短時間で減圧および加圧を行うことができるため、前記減圧工程と前記加圧工程の回数は２回から６回までとすることができる。
In addition, it is preferable that the frequency | count of this pressure reduction process and a pressurization process is 2 to 4 times. Although it is preferable that the number of times of the depressurization step and the pressurization step is large, if the heating time in the vacuum chamber, particularly the peak heating time, is increased to increase the number of times, the amount of flux contained in the solder paste decreases. However, the surface of the solder alloy may be reoxidized.
In addition, since the pressure reduction and pressurization can be performed in a short time when the third pressure (P3) is in the range of 10,000 Pa to 50,000 Pa as described above, the pressure reduction step and the pressure step The number of times can be from 2 to 6.
最後の減圧が終わった後、前記真空チャンバ内の圧力を第３の圧力（Ｐ３）まで加圧し、更にこれを第１の圧力（Ｐ１）まで加圧する。なお、図２に示された第１の圧力（Ｐ１）は最初の第１の圧力（Ｐ１）と同一値で表されているが、大気圧近傍の圧力であれば両者は同一でなくとも良い。また図２に示すように第３の圧力（Ｐ３）までの加圧と第１の圧力（Ｐ１）までの加圧は連続して行っても良く、また一旦第３の圧力（Ｐ３）に加圧した後に第１の圧力（Ｐ１）まで加圧しても良い。前述のように前記真空チャンバ内の加熱時間を延ばさないようにするためには、前者の連続しての加圧が好ましい。 After the final pressure reduction, the pressure in the vacuum chamber is increased to the third pressure (P3), and further increased to the first pressure (P1). In addition, although the 1st pressure (P1) shown by FIG. 2 is represented by the same value as the first 1st pressure (P1), both may not be the same as long as it is a pressure near atmospheric pressure. . In addition, as shown in FIG. 2, the pressurization up to the third pressure (P3) and the pressurization up to the first pressure (P1) may be performed continuously, and once applied to the third pressure (P3). After pressing, the pressure may be increased to the first pressure (P1). As described above, the former continuous pressurization is preferable in order not to extend the heating time in the vacuum chamber.
そして前記真空チャンバ内の圧力が第１の圧力（Ｐ１）にまで到達した以降、前記真空チャンバ内の温度を前記はんだ合金の液相温度以下にまで冷却し、その温度が室温近傍にまで戻った後、基板１１を前記真空チャンバ内より取り出す。
その後、基板１１上に残存するフラックス残渣（図示せず）を洗浄液等で除去し、図１に示すはんだバンプ１０が形成された基板１１が完成する。
Then, after the pressure in the vacuum chamber reaches the first pressure (P1), the temperature in the vacuum chamber is cooled to below the liquidus temperature of the solder alloy, and the temperature returns to near room temperature. Thereafter, the substrate 11 is taken out from the vacuum chamber.
Thereafter, the flux residue (not shown) remaining on the substrate 11 is removed with a cleaning solution or the like, and the substrate 11 on which the solder bumps 10 shown in FIG. 1 are formed is completed.
なお、本実施形態においては、特に図２に示す時間（Ｔ）、即ち第１の圧力（Ｐ１）から第２の圧力（Ｐ２）への減圧と第２の圧力（Ｐ２）から第３の圧力（Ｐ３）への加圧、および加圧により第１の圧力（Ｐ１）への復圧までに要する時間を短くし、またこの間に複数回減圧と加圧を繰り返すことにより、前記はんだ合金の濡れ性等に影響を与えることなく効率よくそのボイドを低減することができる。この時間（Ｔ）は、例えば１２０秒間から２１０秒間程度であることが好ましい。 In the present embodiment, in particular, the time (T) shown in FIG. 2, that is, the pressure reduction from the first pressure (P1) to the second pressure (P2) and the second pressure (P2) to the third pressure are shown. By shortening the time required for pressurization to (P3) and returning to the first pressure (P1) by pressurization, and repeating the depressurization and pressurization several times during this time, wetting of the solder alloy The voids can be efficiently reduced without affecting the properties and the like. This time (T) is preferably about 120 seconds to 210 seconds, for example.
以下、実施例および比較例を挙げて本発明を詳述する。なお、本発明はこれらの実施例に限定されるものではない。 Hereinafter, the present invention will be described in detail with reference to Examples and Comparative Examples. The present invention is not limited to these examples.
＜ソルダペーストの調製＞
ベース樹脂、活性剤および溶剤を適宜混合してフラックスを作製し、これを１２重量％とＳｎ−３Ａｇ−０．５Ｃｕはんだ合金粉末８８重量％（液相温度２２０℃）とをそれぞれ混合し、実施例および比較例に係るソルダペーストを得た。
<Preparation of solder paste>
A base resin, an activator, and a solvent are appropriately mixed to produce a flux, which is mixed with 12 wt% and Sn-3Ag-0.5Cu solder alloy powder 88 wt% (liquid phase temperature 220 ° C.). Solder pastes according to examples and comparative examples were obtained.
バンプ（実施例１から実施例７、比較例１から比較例３、参考例１から参考３）
ＦＲ４基板（Ｃｕ−ＯＳＰ処理、基板レジスト膜２０μｍ、電極ピッチ１３０μｍ、電極開口直径７５μｍ）を使用した。前記ＦＲ４基板に対応するするパターンを有するメタルマスク（マスク厚３０μｍ）を用いて各ソルダペーストを手刷りで印刷した。
Bump (Example 1 to Example 7, Comparative Example 1 to Comparative Example 3, Reference Example 1 to Reference 3)
An FR4 substrate (Cu-OSP treatment, substrate resist film 20 μm, electrode pitch 130 μm, electrode opening diameter 75 μm) was used. Each solder paste was printed by hand printing using a metal mask (mask thickness 30 μm) having a pattern corresponding to the FR4 substrate.
次いで、前記各基板をリフロー装置（製品名：ＳＭＴ Ｓｃｏｐｅ ＳＫ−５０００ 山陽精工株式会社製）を用い、減圧および加圧時以外は大気圧で窒素雰囲気下（酸素濃度１００ｐｐｍ）、図３に示す温度プロファイル、並びに表１および表２に示す条件にてリフローを行い、各試験基板を作製した。 また前記各試験基板について、Ｘ線観察装置（製品名：ＸＤ７６００ Ｄｉａｍｏｎｄ、Ｎｏｒｄｓｏｎ Ｃｏｒｐｏｒａｔｉｏｎ社製）を用い、形成されたはんだバンプに占めるボイドの面積率を評価した。その結果を表１および表２に表す。
なお、表１および表２において第２の圧力への減圧タイミングは、いずれも昇温時の前記リフロー装置内の温度到達時を表す。
Next, each substrate was subjected to a reflow apparatus (product name: SMT Scope SK-5000, manufactured by Sanyo Seiko Co., Ltd.) under a nitrogen atmosphere at atmospheric pressure (
In Tables 1 and 2, the depressurization timing to the second pressure represents the time when the temperature in the reflow apparatus reaches the temperature when the temperature is raised.
表１および表２に表されるように、実施例１から実施例７のいずれもボイド面積率は１０％未満となり、ボイド低減効果のあることが分かる。
また実施例６および実施例７のように、第３の圧力を１０，０００Ｐａから５０，０００Ｐａとした場合、短時間に減圧−加圧回数を６回行っても良好なボイド低減効果を発揮することができる。
更に特に実施例４のように第３の圧力を１０，０００Ｐａとし、減圧−加圧回数を４回とすると、前記基板上に塗布されたソルダペーストが第１の圧力よりも低圧力下且つ高温下（はんだ合金の溶融温度以上）に曝される時間を少なくしつつ減圧−加圧を繰り返すことにより、フラックス量の減少を防ぎつつよりよいボイド低減効果を発揮することができることが分かる。
As shown in Table 1 and Table 2, in all of Examples 1 to 7, the void area ratio is less than 10%, indicating that there is an effect of reducing voids.
Further, as in Example 6 and Example 7, when the third pressure is set to 10,000 Pa to 50,000 Pa, a good void reduction effect is exhibited even if the number of times of decompression-pressurization is performed six times in a short time. be able to.
Further, in particular, when the third pressure is 10,000 Pa and the number of times of pressure reduction and pressurization is 4 times as in Example 4, the solder paste applied on the substrate has a lower pressure and a higher temperature than the first pressure. It can be seen that a better void reduction effect can be exhibited while preventing a decrease in the flux amount by repeating the reduced pressure-pressurization while reducing the time of exposure to below (the melting temperature of the solder alloy or higher).
１０…はんだバンプ
１１…基板
10 ... Solder bump 11 ... Substrate
Claims (7)
フラックスおよびはんだ合金からなるソルダペーストを前記ワーク上の所定の位置に印刷する工程と、
前記ワークを大気圧の近傍である第１の圧力下にて加熱する工程と、
前記ワークを加熱する加熱温度が前記はんだ合金の液相温度近傍以上になった以降に前記ワーク周囲の圧力を前記第１の圧力よりも低い第２の圧力まで減圧する工程と、
前記加熱温度が前記はんだ合金の液相温度以上の状態で前記ワーク周囲の圧力を前記第２の圧力よりも高い第３の圧力まで加圧する工程と、
前記加熱温度が前記はんだ合金の液相温度以上の状態で前記ワーク周囲の圧力を前記第１の圧力まで加圧する工程と、
前記ワーク周囲の圧力が前記第１の圧力に到達した以降に前記加熱温度を前記はんだ合金の液相温度以下にして前記ワーク上にはんだバンプを形成する工程とを含み、
前記第２の圧力まで減圧する工程と前記第３の圧力まで加圧する工程とを複数回行うことを特徴とするはんだバンプの形成方法。 A method of forming solder bumps on a workpiece,
Printing a solder paste made of a flux and a solder alloy at a predetermined position on the workpiece;
Heating the workpiece under a first pressure that is near atmospheric pressure;
Reducing the pressure around the workpiece to a second pressure lower than the first pressure after the heating temperature for heating the workpiece has reached or exceeded the liquid phase temperature of the solder alloy;
Pressurizing the pressure around the workpiece to a third pressure higher than the second pressure in a state where the heating temperature is equal to or higher than the liquid phase temperature of the solder alloy;
Pressurizing the pressure around the workpiece to the first pressure in a state where the heating temperature is equal to or higher than the liquid phase temperature of the solder alloy;
Forming a solder bump on the workpiece by setting the heating temperature to be equal to or lower than the liquid phase temperature of the solder alloy after the pressure around the workpiece reaches the first pressure,
A method for forming a solder bump, wherein the step of reducing the pressure to the second pressure and the step of increasing the pressure to the third pressure are performed a plurality of times.
2. The cycle time of one cycle from depressurization from the first pressure to the second pressure to pressurization to the third pressure is 10 seconds to 40 seconds. The method for forming a solder bump according to claim 6.
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