JP3691972B2 - How to attach solder to pads - Google Patents

How to attach solder to pads Download PDF

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Publication number
JP3691972B2
JP3691972B2 JP29861798A JP29861798A JP3691972B2 JP 3691972 B2 JP3691972 B2 JP 3691972B2 JP 29861798 A JP29861798 A JP 29861798A JP 29861798 A JP29861798 A JP 29861798A JP 3691972 B2 JP3691972 B2 JP 3691972B2
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Prior art keywords
solder
pad
substrate
opening
temperature
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JP2000124594A (en
Inventor
敏幸 中田
泰夫 岩崎
義仁 奥脇
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Fujitsu Ltd
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Fujitsu Ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L24/00—Arrangements for connecting or disconnecting semiconductor or solid-state bodies; Methods or apparatus related thereto
    • H01L24/74—Apparatus for manufacturing arrangements for connecting or disconnecting semiconductor or solid-state bodies
    • H01L24/741—Apparatus for manufacturing means for bonding, e.g. connectors
    • H01L24/743—Apparatus for manufacturing layer connectors
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2224/00—Indexing scheme for arrangements for connecting or disconnecting semiconductor or solid-state bodies and methods related thereto as covered by H01L24/00
    • H01L2224/74—Apparatus for manufacturing arrangements for connecting or disconnecting semiconductor or solid-state bodies and for methods related thereto
    • H01L2224/741—Apparatus for manufacturing means for bonding, e.g. connectors
    • H01L2224/743—Apparatus for manufacturing layer connectors
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
    • H01L2924/013—Alloys
    • H01L2924/0132—Binary Alloys
    • H01L2924/01322—Eutectic Alloys, i.e. obtained by a liquid transforming into two solid phases

Abstract

PROBLEM TO BE SOLVED: To provide a method of applying solder to a pad which is excellent in wettability and where spare solder can be formed. SOLUTION: A solder applying method is carried out through a manner where a solder 22 is supplied to a pad 18 by feeding solder paste 16 to the pad 18 surrounded with a protective insulating layer 12 and heating it for reflow, where the temperature rise rate of the board 10 is set at 14 deg.C/minute to 17 deg.C/ minute in a temperature rise region from the temperature of the board 10 lower than a melting point of solder by about 7 deg.C to the temperature higher than the former temperature by about 7 deg.C when the board 10 is heated for reflowing in a reflow oven, and the board 10 is primarily heated from below its rear side.

Description

【０００１】
【発明の属する技術分野】
本発明はパッドへのはんだ付着方法に関する。
【０００２】
【従来の技術】
プリント配線板（基板）の配線パターン上にはんだレジストによる保護絶縁層を形成し、この保護絶縁層の開口部に露出させたパッドに、印刷法などにより電子部品などの電極やリードを接合するための導体ペースト（はんだペースト）を供給している。
【０００３】
開口部内に充填されたはんだペーストは、基板を連続炉中で加熱することによりリフローされ、パッドに付着される。
このパッドに付着されるはんだは、通常予備はんだと称され、比較的低融点のはんだ（共晶はんだ）が用いられる。実装されるベアチップ等の電子部品側には比較的高融点のはんだバンプが形成されており、上記の予備はんだを介して基板に接合される。
【０００４】
【発明が解決しようとする課題】
ところで昨今は半導体チップなどの電子部品の高密度化が進行し、パッドのピッチが２５０μｍ以下となり、パッド径も１００μｍ程度と極めて小さくなっている。したがって、保護絶縁層の開口部も縮小され、そのためパッドへの予備はんだの形成が困難になってきている。
【０００５】
発明者等が検討したところ、保護絶縁層の開口部の開口径が小さくなってきていることから、開口部内に充填されたはんだペーストが、溶融時に表面張力で球形となり（図６）、パッドに濡れにくく、したがって十分な量の予備はんだの形成が行えないことが判明した。
はんだペーストの量を多くすればする程、予想に反して十分な予備はんだの形成が行えないことも判明した。
【０００６】
本発明は上記課題を解決すべくなされたものであり、その目的とするところは、濡れ性よく予備はんだを形成できるパッドへのはんだ付着方法を提供するにある。
【０００７】
【課題を解決するための手段】
本発明は上記目的を達成するため次の構成を備える。
すなわち、本発明に係るパッドへのはんだ付着方法では、はんだペーストを、基板の保護絶縁層に囲まれたパッドに供給してリフロー加熱することによりパッド上にはんだを付着するはんだ付着方法において、はんだペーストを複数回に分けて供給し、１回目のはんだ供給量Ｂを、パッドを囲む保護絶縁層の開口部の開口半径をＡ、パッド表面から保護絶縁層表面までの開口部の深さをｔとしたとき、
式：
【数２】

Figure 0003691972
を満足する量のはんだペーストをパッドに供給してリフロー加熱し、次いで２回目以降のはんだペーストの供給とリフロー加熱を行ってパッド上に必要量の予備はんだを形成することを特徴とする。
【０００８】
前記リフロー加熱時、リフロー炉内で基板を加熱する際、基板温度がはんだの融点より約７℃低い温度から約７℃高い温度となる昇温領域で、基板の昇温速度を１４℃／分〜１７℃／分となるように調整すると共に、基板を主として基板の下面側から加熱するようにすると好適である。
【０００９】
【発明の実施の形態】
以下、本発明の好適な実施の形態を添付図面に基づいて詳細に説明する。
〔第１の実施の形態〕
まず図１に示すように、プリント配線基板１０の保護絶縁層（ソルダーレジスト層）１２に形成された開口部１４内に、印刷マスクを用いた印刷法または転写スタンプを用いた転写法により、導体ペースト（はんだペースト）１６を充填する。１８はパッドである。
【００１０】
はんだペースト１６は、任意のはんだを粒径２５μｍ以下の球形に加工した微細なソルダーボール１６ａを高活性のフラックスでペースト状に練ったものである。
【００１１】
開口部１４の開口径は１００μｍ以下であるから、粒径２５μｍ以下の微細なソルダーボール１６ａとはいえ、開口部１４に対して図示のようにかなり大きなものとなる。
【００１２】
上記のように開口部１４内に充填したはんだペースト１６をリフロー炉内で窒素雰囲気中でリフロー加熱し、予備はんだに形成する。
発明者等は、従来においては、リフロー炉内では基板の表面側からの加熱量が多く、したがって、はんだペースト１６の表面側のソルダーボール１６ａが加熱されて溶融し、その表面張力が奥側のソルダーボール１６ａに作用して、奥側のソルダーボール１６ａを抱き込むような状態となり、したがって奥側のソルダーボール１６ａが溶融してパッド１８を濡らす前に、全体が球形になってしまい、パッド１８に付着しにくい（図６）ことに想到した。
【００１３】
そこで、本実施の形態では、基板１０の加熱を主として基板１０の下面側から行うようにした。
すなわちリフロー炉内で、基板１０の下面側を加熱するヒータを多くし、開口部１４内に充填されたはんだペースト１６中の開口部１４奥側のソルダーボール１６ａも溶融するようにする。好ましくは、開口部１４の入口側のソルダーボール１６ａよりも奥側のソルダーボール１６ａの方が早く溶融するようにする。
【００１４】
また、はんだが溶融するはんだの融点付近の昇温速度を緩やかになるように設定する。
共晶はんだの場合の融点は１８３℃である。
この前後約７℃の領域、すなわち基板１０の温度が約１７６℃〜１９０℃の温度領域の昇温時間を約１分程度と長くする。基板１０温度は熱電対で計測する。
【００１５】
図４は基板温度プロファイルを示す。ｔ１（１７６℃）〜ｔ２（１９０℃）の温度領域を１分間程度の長時間をかけて昇温する。この昇温レートは１４℃／分〜１７℃／分が好ましい。最終的にはｔ３（２１０℃以上）まで加熱して確実にはんだを溶融させる。
【００１６】
上記のように、はんだの融点前後の昇温速度を緩やかに設定することで、確実に基板１０下面側の温度が表面側の温度より早く上昇し、開口部１４内の奥側のソルダーボール１６ａが溶融してパッド１８に付着し（図２）、次いで全体のソルダーボール１６ａが溶融して、図３に示すように、パッド１８に全面に付着した予備はんだ２０が得られる。
なお従来は、リフロー加熱の融点付近の昇温時間が１０秒〜２０秒程度と短い。
【００１７】
上記のように、一旦はんだがパッド１８に付着したら、図６のようなパッドから分離した球状となることはない。
【００１８】
〔第２の実施の形態）
次にはんだの供給量について検討する。発明者等は、前記のように保護絶縁層の開口部が小さくなるにつれ、はんだの濡れ性が悪くなることから、はんだ量を多くすることを試みたが、逆に多くすると球形になってしまうことを見いだした。
【００１９】
はんだが球形になると、図６のように、球形になったはんだがパッド１８に接触せず、ためにパッド１８に付着しないことになるのである。
そこで、はんだの供給量（体積）を、例え球形になったとしてもパッド１８に接触する量、すなわち、球形のはんだが開口部１４内に入り込んでパッド１８に接触する条件を検討した。
【００２０】
図５に示すように、開口部１４の開口径を２Ａ、パッド１８表面から保護絶縁層１２の表面までの開口部１４の深さをｔとしたとき、球２２が、パッド１８に接触する条件は、はんだの体積Ｂが、
式
【数３】
Figure 0003691972
で表される量以下であることがわかる。
なおはんだの体積Ｂは、はんだペースト中のソルダーボールの体積である。はんだペースト中のソルダーボールの体積ははんだペーストの組成から計算できる。
【００２１】
はんだの体積Ｂが上記より大きいと、図６に示すようにパッド１８に接触しないことになる。
【００２２】
そこで、はんだ量を上記式で表される量（推定最大はんだ量）よりも少ないようにしてはんだの濡れ性を試験した結果を表１に示す。
【表１】
Figure 0003691972
【００２３】
表１から明らかなように、はんだ供給量が推定最大はんだ量（Ｂｍａｘ）に近くなると濡れ不良が発生するようになる。
したがって、はんだの供給量を上記式で表される量以下になるようにする。
【００２４】
なお、はんだペーストを複数回に分けて供給して必要量の予備はんだを得る場合には、１回目のはんだ供給量を上記式で表される量より小さくする。２回目以降のはんだペースト供給の場合には、１回目の供給によりはんだがパッドに付着しているので、はんだの濡れ性は良好となる。
【００２５】
上記のように、はんだの供給量を制限すると共に、前記第１の実施形態におけるリフロー加熱条件を併用すると一層はんだの濡れ性が向上する。
【００２６】
また、一定のはんだ付性を得るために、はんだの供給量（Ｂ）が決まっているときは、保護絶縁層の開口部の開口半径Ａ、およびパッド表面から保護絶縁層の表面までの開口部の深さｔを、式：
【数４】
Figure 0003691972
を満足するように、プリント配線基板１０の設計を行うようにする。
これにより、パッド１８に密着した必要量の予備はんだ２０を確保できる。
【００２７】
【発明の効果】
本発明によれば、１回目のはんだ供給量を上記式で表される量よりも小さくすることによって、２回目以降のはんだペースト供給の場合に、１回目の供給によりはんだがパッドに付着しているので、はんだの濡れ性が良好となる。
【図面の簡単な説明】
【図１】 はんだペーストをパッドに供給した状態の説明図、
【図２】 開口部奥側のソルダーボールが溶融した状態の説明図、
【図３】 予備はんだが形成された状態の説明図、
【図４】 基板温度プロファイルを示すグラフ、
【図５】 はんだの球体がパッドに接触している状態を示す説明図、
【図６】 はんだが球状になって分離した状況を示す説明図である。
【符号の説明】
１０ プリント配線基板
１２ 保護絶縁層
１４ 開口部
１６ はんだペースト
１６ａ ソルダーボール
１８ パッド
２０ 予備はんだ[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for attaching solder to a pad.
[0002]
[Prior art]
To form a protective insulation layer with solder resist on the wiring pattern of a printed wiring board (substrate), and to bond electrodes and leads of electronic components to the pads exposed in the opening of this protective insulation layer by printing The conductor paste (solder paste) is supplied.
[0003]
The solder paste filled in the opening is reflowed by heating the substrate in a continuous furnace and attached to the pad.
The solder attached to this pad is usually called a preliminary solder, and a solder having a relatively low melting point (eutectic solder) is used. A solder bump having a relatively high melting point is formed on the electronic component side such as a bare chip to be mounted, and is bonded to the substrate via the preliminary solder.
[0004]
[Problems to be solved by the invention]
Nowadays, the density of electronic components such as semiconductor chips is increasing, the pad pitch is 250 μm or less, and the pad diameter is as small as about 100 μm. Therefore, the opening of the protective insulating layer is also reduced, which makes it difficult to form preliminary solder on the pad.
[0005]
As a result of investigations by the inventors, the opening diameter of the opening of the protective insulating layer has become smaller, so that the solder paste filled in the opening becomes spherical due to surface tension when melted (FIG. 6), and is applied to the pad. It has been found that it is difficult to wet and therefore a sufficient amount of pre-solder cannot be formed.
It has also been found that as the amount of solder paste is increased, sufficient preliminary solder cannot be formed contrary to expectations.
[0006]
The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a method for attaching a solder to a pad that can form a preliminary solder with good wettability.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, the present invention comprises the following arrangement.
That is, in the method of attaching a solder to a pad according to the present invention, in the method of attaching a solder to a pad by supplying a solder paste to the pad surrounded by the protective insulating layer of the substrate and performing reflow heating, The paste is supplied in a plurality of times, and the first solder supply amount B is set such that the opening radius of the opening of the protective insulating layer surrounding the pad is A, and the depth of the opening from the pad surface to the protective insulating layer surface is t. When
formula:
[Expression 2]
Figure 0003691972
Is supplied to the pad and reflow-heated, and then the second and subsequent solder pastes are supplied and reflow-heated to form a necessary amount of preliminary solder on the pad.
[0008]
During the reflow heating, when the substrate is heated in the reflow furnace, the substrate heating rate is 14 ° C./min in a temperature rising region where the substrate temperature is about 7 ° C. higher than the melting point of the solder. It is preferable to adjust the temperature to ˜17 ° C./min and to heat the substrate mainly from the lower surface side of the substrate.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described in detail with reference to the accompanying drawings.
[First Embodiment]
First, as shown in FIG. 1, a conductor is formed in the opening 14 formed in the protective insulating layer (solder resist layer) 12 of the printed wiring board 10 by a printing method using a printing mask or a transfer method using a transfer stamp. A paste (solder paste) 16 is filled. Reference numeral 18 denotes a pad.
[0010]
The solder paste 16 is obtained by kneading a fine solder ball 16a obtained by processing an arbitrary solder into a spherical shape having a particle diameter of 25 μm or less into a paste with a highly active flux.
[0011]
Since the opening diameter of the opening 14 is 100 μm or less, the solder ball 16 a having a particle diameter of 25 μm or less is considerably larger than the opening 14 as illustrated.
[0012]
The solder paste 16 filled in the opening 14 as described above is reflow-heated in a nitrogen atmosphere in a reflow furnace to form a preliminary solder.
The inventors of the present invention conventionally have a large amount of heating from the surface side of the substrate in the reflow furnace, and therefore, the solder balls 16a on the surface side of the solder paste 16 are heated and melted, and the surface tension is on the back side. The solder ball 16a acts on the solder ball 16a so as to embrace the solder ball 16a. Therefore, before the solder ball 16a on the inner side melts and wets the pad 18, the entire ball 18a becomes spherical. It was thought that it was hard to adhere to (FIG. 6).
[0013]
Therefore, in this embodiment, the substrate 10 is heated mainly from the lower surface side of the substrate 10.
That is, in the reflow furnace, the number of heaters for heating the lower surface side of the substrate 10 is increased so that the solder balls 16a on the inner side of the opening 14 in the solder paste 16 filled in the opening 14 are also melted. Preferably, the solder ball 16a on the back side melts faster than the solder ball 16a on the entrance side of the opening 14.
[0014]
In addition, the rate of temperature rise near the melting point of the solder where the solder melts is set to be gentle.
In the case of eutectic solder, the melting point is 183 ° C.
Before and after this, the temperature raising time in the region of about 7 ° C., that is, the temperature region in which the temperature of the substrate 10 is about 176 ° C. to 190 ° C. is increased to about 1 minute. The substrate 10 temperature is measured with a thermocouple.
[0015]
FIG. 4 shows the substrate temperature profile. The temperature is raised in a temperature range from t1 (176 ° C.) to t2 (190 ° C.) over a long time of about 1 minute. The temperature rising rate is preferably 14 ° C./min to 17 ° C./min. Finally, the solder is surely melted by heating to t3 (210 ° C. or higher).
[0016]
As described above, by gradually setting the rate of temperature rise before and after the melting point of the solder, the temperature on the lower surface side of the substrate 10 surely rises faster than the temperature on the front surface side, and the solder balls 16a on the back side in the openings 14 Is melted and attached to the pad 18 (FIG. 2), and then the entire solder ball 16a is melted, and as shown in FIG. 3, the preliminary solder 20 attached to the entire surface of the pad 18 is obtained.
Conventionally, the temperature rise time near the melting point of reflow heating is as short as about 10 seconds to 20 seconds.
[0017]
As described above, once the solder adheres to the pad 18, it does not become a spherical shape separated from the pad as shown in FIG.
[0018]
[Second Embodiment]
Next, consider the amount of solder supplied. The inventors tried to increase the amount of solder because the wettability of the solder deteriorated as the opening of the protective insulating layer became smaller as described above, but conversely, if it increased, it became spherical. I found out.
[0019]
When the solder becomes spherical, as shown in FIG. 6, the spherical solder does not contact the pad 18 and therefore does not adhere to the pad 18.
Therefore, the amount (volume) of the solder that is brought into contact with the pad 18 even when it becomes spherical, that is, the condition that the spherical solder enters the opening 14 and contacts the pad 18 was examined.
[0020]
As shown in FIG. 5, when the opening diameter of the opening 14 is 2A and the depth of the opening 14 from the surface of the pad 18 to the surface of the protective insulating layer 12 is t, the condition that the sphere 22 contacts the pad 18 Is the volume B of the solder,
Formula 3
Figure 0003691972
It can be seen that the amount is less than or equal to.
The solder volume B is the volume of the solder balls in the solder paste. The volume of the solder ball in the solder paste can be calculated from the composition of the solder paste.
[0021]
When the volume B of the solder is larger than the above, the pads 18 are not contacted as shown in FIG.
[0022]
Therefore, Table 1 shows the results of testing the solder wettability by making the solder amount smaller than the amount represented by the above formula (estimated maximum solder amount).
[Table 1]
Figure 0003691972
[0023]
As is apparent from Table 1, when the solder supply amount approaches the estimated maximum solder amount (Bmax), wetting failure occurs.
Therefore, the solder supply amount is set to be equal to or less than the amount represented by the above formula.
[0024]
In addition, when the solder paste is supplied in a plurality of times and a necessary amount of preliminary solder is obtained, the first solder supply amount is made smaller than the amount represented by the above formula. In the case of supplying the solder paste from the second time onward, the solder adheres to the pad by the first supply, so that the wettability of the solder becomes good.
[0025]
As described above, when the supply amount of the solder is limited and the reflow heating condition in the first embodiment is used in combination, the wettability of the solder is further improved.
[0026]
In addition, in order to obtain a certain solderability, when the supply amount (B) of the solder is determined, the opening radius A of the opening of the protective insulating layer and the opening from the pad surface to the surface of the protective insulating layer The depth t of the equation:
[Expression 4]
Figure 0003691972
The printed wiring board 10 is designed so as to satisfy the above.
Thereby, it is possible to secure the necessary amount of preliminary solder 20 in close contact with the pad 18.
[0027]
【The invention's effect】
According to the present invention, when the solder supply amount for the first time is made smaller than the amount represented by the above formula, in the case of supplying the solder paste for the second time and thereafter, the solder adheres to the pad by the first supply. As a result, the solder wettability is improved.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of a state in which solder paste is supplied to a pad;
FIG. 2 is an explanatory view showing a state where a solder ball on the back side of the opening is melted,
FIG. 3 is an explanatory diagram of a state in which preliminary solder is formed;
FIG. 4 is a graph showing a substrate temperature profile;
FIG. 5 is an explanatory diagram showing a state in which a solder sphere is in contact with a pad;
FIG. 6 is an explanatory diagram showing a situation in which solder has become spherical and separated.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Printed wiring board 12 Protective insulating layer 14 Opening part 16 Solder paste 16a Solder ball 18 Pad 20 Preliminary solder

Claims (2)

はんだペーストを、基板の保護絶縁層に囲まれたパッドに供給してリフロー加熱することによりパッド上にはんだを付着するはんだ付着方法において、
はんだペーストを複数回に分けて供給し、
１回目のはんだ供給量Ｂを、
パッドを囲む保護絶縁層の開口部の開口半径をＡ、パッド表面から保護絶縁層表面までの開口部の深さをｔとしたとき、
式：
Figure 0003691972
 を満足する量のはんだペーストをパッドに供給してリフロー加熱し、
次いで２回目以降のはんだペーストの供給とリフロー加熱を行ってパッド上に必要量の予備はんだを形成することを特徴とするパッドへのはんだ付着方法。 In a solder adhesion method in which solder paste is supplied to a pad surrounded by a protective insulating layer of a substrate and reflow heated to adhere the solder onto the pad.
Supply solder paste in several times,
The first solder supply amount B is
When the opening radius of the opening of the protective insulating layer surrounding the pad is A, and the depth of the opening from the pad surface to the protective insulating layer surface is t,
formula:
Figure 0003691972
 A sufficient amount of solder paste is supplied to the pad and reflow heated.
Next, a method for attaching a solder to a pad, comprising supplying a solder paste for the second time and subsequent and performing reflow heating to form a necessary amount of preliminary solder on the pad. 前記リフロー加熱時、リフロー炉内で基板を加熱する際、基板温度がはんだの融点より約７℃低い温度から約７℃高い温度となる昇温領域で、基板の昇温速度を１４℃／分〜１７℃／分となるように調整すると共に、基板を主として基板の下面側から加熱することを特徴とする請求項１記載のパッドへのはんだ付着方法。During the reflow heating, when the substrate is heated in the reflow furnace, the substrate temperature increase rate is 14 ° C./min in a temperature rising region where the substrate temperature is about 7 ° C. higher than the melting point of the solder. The method for adhering solder to a pad according to claim 1, wherein the temperature is adjusted to -17 ° C / min and the substrate is heated mainly from the lower surface side of the substrate.
JP29861798A 1998-10-20 1998-10-20 How to attach solder to pads Expired - Fee Related JP3691972B2 (en)

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JP4502496B2 (en) * 2000-11-16 2010-07-14 富士通株式会社 Solder shape evaluation method for BGA mounting, solder shape evaluation apparatus for BGA mounting, and computer-readable recording medium storing a solder shape evaluation program for BGA mounting

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