JP2000277898A - Board for mounting of ball grid array package - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a board, for the mounting of a BGA package, in which stress is not concentrated in a connection place due to the difference in coefficients of thermal expansion between a BGA package board and a board for the mounting of the package and whose connection reliability is high. SOLUTION: In a board comprising a pad for connection, which is formed so as to correspond to a solder ball on a BGA package, a pad 32 for connection is formed on an insulating board 31 to be in a terrace shape, in such a way that its lower layer is made larger than the diameter of the solder ball and that its upper layer is nearly identical to the diameter of the solder ball. In addition, a first solder resist 35 which comprises an opening 36, whose diameter is nearly equal to the diameter of the lower layer of the pad 32 for connection is formed on the insulating board 31. A second solder resist 37 which comprises an opening 38, whose diameter is nearly equal to the diameter of the solder ball, is formed on it in such a way that both openings are aligned on the same axis. Thereby, this board for the mounting of the BGA package is obtained. A solder ball which is melted inside the openings 36, 38 forms a wedge-shaped solder bump.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a substrate having connection pads provided in correspondence with solder balls of a ball grid array (hereinafter referred to as "BGA") package. The present invention relates to a structure of a connection pad that can improve connection reliability with a solder ball.

[0002]

2. Description of the Related Art In recent years, as single-chip modules have been replaced with multi-chip modules, high-density packaging and high-speed packaging have been required, and the number of I / O pins has been increasing. There is a BGA package as a package in consideration of these points. BGA is 1.0 to 1.5 mm on the back surface of the substrate on which the semiconductor is mounted and wired.
Input / output electrode pads are formed in a grid pattern at a pitch equal to or less than the pitch, and spherical ball-shaped terminals made of solder (hereinafter referred to as solder balls) are formed thereon.

As a method of mounting the BGA, a solder paste or a flux is applied to connection pads of a substrate made of a resin, a ceramic, or the like, and solder balls of a BGA package are placed on the connection pads so as to face the reflow solder. Both are joined by a ring method. Such connection pads of the substrate are generally formed by panel plating, pattern plating, vapor deposition, or printing.

FIG. 4 is a side view of a printed wiring board formed by a panel plating method on the substrate. The printed wiring board 10 is obtained by etching a copper clad laminate and connecting pads (hereinafter referred to as pads). After the formation of 1), a solder resist 2 is formed using a resist film or the like in order to secure insulation between patterns including the pad 1. Reference numeral 3 denotes a resin substrate as a core material of the copper-clad laminate.

FIG. 5 is a side view showing a state in which a BGA package is mounted on the printed wiring board 10. As shown in FIG. In this figure, reference numeral 21 denotes a substrate of the BGA package 20, which is an I / O pad 22 for connecting to a motherboard such as a printed wiring board provided on the back side of the mounting surface of a semiconductor chip or the like.
A solder ball 23 is formed thereon.

[0006] The BGA package 20 uses a mounting machine such as a mounter to mount solder balls 23 serving as connection terminals on predetermined pads 1 of the printed wiring board 10 to which solder paste or flux has been applied in advance, and then performs reflow heating. Melts the solder ball 23 and joins it to the pad 1 of the printed wiring board 10 by soldering.

FIG. 6 is a side view showing this joining state.
The solder bumps 24 formed by joining the solder balls 23 to the pads 1 are restricted from spreading during melting by the pads 1 and the solder resist 2 of the printed wiring board 10, and have a barrel-like shape due to the surface tension of the solder bumps 24 themselves. .

[0008]

However, in the above-mentioned conventional method, the printed wiring board 10 and the substrate of the BGA package 20 have a difference in thermal expansion coefficient due to a difference in material, and when the two are connected by soldering. Due to the effect of the applied heat, the solder bump 24 and the pad 1 of the printed wiring board 10 and the I / O pad 2 of the BGA package 20
Stress is concentrated at the connection points 5 and 25 with the connection 2, and cracks occur at these points, deteriorating the reliability of the connection and eventually breaking the electrical connection.

The present invention has been made to solve such a conventional problem. Even if the BGA mounting substrate and the BGA package substrate have a difference in the coefficient of thermal expansion, the connection reliability is not reduced. It is an object of the present invention to provide a board for mounting a ball grid array package in which the I / O pads of the board and the BGA can be easily aligned.

[0010]

According to a first aspect of the present invention, there is provided a substrate having connection pads provided in correspondence with solder balls of a ball grid array package, wherein a lower layer of the solder balls is provided. A connection pad formed on the substrate in a stepped shape with a diameter larger than the diameter and an upper layer having substantially the same diameter as the diameter of the solder ball; and a diameter of a lower layer of the connection pad formed on the substrate. A first solder resist having an opening having a substantially equal diameter, an opening having a diameter substantially equal to the diameter of the solder ball, and the opening being coaxially aligned with the opening of the first solder resist to form the first solder resist; Second formed on solder resist
And a solder resist.

[0011] With this configuration of the substrate, the solder ball fits into the opening formed in the second solder resist, and the solder ball and the connection pad are accurately positioned.
Further, the solder balls melted in the cavities formed by the openings of the first and second solder resists flow down following the step-like connection pads to form wedge-shaped solder bumps.

According to a second aspect of the present invention, the first solder resist and the second solder resist each have a thickness of:
It is characterized in that the radius is approximately one half of the radius of the solder ball. For this reason, while the solder balls and the connection pads can be accurately positioned, the ball grid array package that sinks due to the melting of the solder balls does not come into contact with the second solder resist, and solder bumps having a desired shape are formed.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below with reference to FIGS. 1 to 3 are views showing a step of forming a wedge-shaped solder bump according to an embodiment of the present invention. FIG. 1 is a sectional view of a printed wiring board for package mounting. In the figure, reference numeral 30 denotes a printed wiring board, on which connection pads 32 formed in two layers of terraces are formed corresponding to the solder balls of the BGA package, respectively.

The connection pads 32 are formed by attaching a photoresist to copper foil on an insulating substrate 31 of a copper-clad laminate, which is a material of the printed wiring board 30, at respective positions corresponding to solder balls of a BGA package. A photomask for shielding a light-shielding area from the other area while leaving an area slightly larger than the diameter of the solder ball is developed after exposure, and the connection pad 3 is formed.
The portion of the pad 33 in the lower layer 2 is covered with a photoresist. In this state, the copper foil other than the pads 33 is removed by etching, and then the photoresist on the pads 33 is peeled off.

Next, a photoresist is stuck on the entire surface of the insulating substrate 31 including the pads 33 formed in this manner, and a photomask is provided at a position corresponding to the pad 33 to shield a region having substantially the same diameter as the diameter of the solder ball. Are formed by exposing and developing after exposure, a region other than the portion to be the pad 34 is covered with a photoresist, and electrolytic copper plating is performed to form an upper layer pad 34, and the photoresist is peeled off.

Next, on the insulating substrate 31 provided with the connection pads 32 formed in a two-layered terrace shape in this manner,
A first solder resist 35 having a thickness of approximately one-half the radius of the solder ball of the BGA package and having an opening 36 formed around a lower layer pad 33 of the pad 32 with a predetermined gap left is attached. . Further, the first solder resist 35
BG having the same thickness as the first solder resist 35
Opening 38 approximately equal to the diameter of the solder ball in package A
The second solder resist 37 formed with is formed.

If the thickness of the solder resists 35 and 37 is insufficient, a plurality of solder resists may be stacked to have a required thickness. At this time, the lowermost solder resist 35
The opening provided in the solder resist inserted between the solder resist 37 of the uppermost layer and the outer edge of the opening 36 provided in the solder resist 35 of the lowermost layer and the opening 38 provided in the solder resist 37 of the uppermost layer as long as it does not contact the pad 32. It is preferable that the diameter is set so as to be located substantially on a straight line connecting the outer edge of the lens.

The first and second solder resists 3
As for Nos. 5 and 37, a dry film type in which an epoxy resin is combined with an acrylic base is suitable for handling. A positive or negative film on which a desired pattern including openings 36 and 38 is drawn is brought into close contact, and the pattern is exposed to ultraviolet light. Then, it is formed by developing using an organic solvent or an aqueous solution, dissolving and removing unnecessary portions including the openings 36 and 38, and then thermally curing.

FIG. 2 shows a state in which the BGA package is mounted on the printed wiring board 30 produced in this manner.
FIG. 2 is a side view showing a state in which the BGA package 20 is mounted on the printed wiring board 30. The BGA package 20 has been determined in advance by using a mounting machine such as a mounter. The solder balls 23 serving as connection terminals are mounted on the pads 32, and then the solder balls 23 are melted by reflow heating, and are joined to the pads 32 of the printed wiring board 30 by soldering.

In FIG. 2, the thicknesses of the solder resists 35 and 37 are the same as those of the solder balls 23 of the BGA package 20.
Are formed at approximately one-half of the radius of. Accordingly, the sum of the heights of the solder resists 35 and 37 is equal to the radius of the solder ball 23, and the solder ball 23 of the BGA package 20 is
It fits into the concave portion 39 formed by the upper solder resists 35 and 37 and the pad 32.

FIG. 3 shows the solder balls 23 and the pads 32.
FIG. 4 is a side view showing a bonding state of the solder resist 23 of the printed wiring board 30 during reflow heating.
In the recess 39 formed by the pads 5 and 37 and the pad 32, the pad 34 is attracted to the outer edge of the lower layer pad 33,
Accordingly, the diameter of the intermediate portion of the solder bump 25 is regulated, and the wedge-shaped bump 25 can be forcibly formed.

[0022]

As described above, the ball grid array package mounting board according to the first invention of the present application is a board having connection pads provided respectively corresponding to the solder balls of the ball grid array package.
A lower pad having a diameter larger than the diameter of the solder ball, an upper layer having a diameter substantially equal to the diameter of the solder ball, a connection pad formed on the substrate in a stepped shape, and a connection pad formed on the substrate, A first solder resist having an opening having a diameter substantially equal to the diameter of the lower layer of the pad; and an opening having a diameter substantially equal to the diameter of the solder ball, and the opening and the opening of the first solder resist are coaxially aligned. And the second solder resist formed on the first solder resist. Therefore, the solder ball is formed in the space formed by the two-layer step-shaped pads and the openings of the first to third resists. Molten solder flows into the printed circuit board and BGA
The shape of the solder ball between the packages is formed in a wedge shape with a stress buffering function, stress is not concentrated on the connection points between the solder bumps and the pads of the printed wiring board and the electrodes of the BGA package, and heat is applied to the printed wiring board and the BGA package board. Even if there is a difference in the expansion coefficient, the connection reliability does not decrease. Further, since the solder ball of the BGA package fits into the opening of the solder resist in the uppermost layer of the printed wiring board, the positioning of both can be performed accurately and easily.

According to a second aspect of the present invention, the first solder resist and the second solder resist have respective thicknesses of:
Since the radius of the solder ball is set to approximately one-half, the ball grid array package that sinks due to the melting of the solder ball contacts the second solder resist while the solder ball and the connection pad can be accurately positioned. Thus, a solder bump having a desired shape is formed.

[Brief description of the drawings]

FIG. 1 is a side sectional view of a ball grid array package mounting substrate according to the present invention.

FIG. 2 is a side sectional view showing a state where a ball grid array package is mounted on a ball grid array package mounting substrate according to the present invention.

FIG. 3 is a side sectional view showing a bonding state between a solder ball and a pad according to the present invention.

FIG. 4 is a side sectional view of a conventional ball grid array package mounting substrate.

FIG. 5 is a side sectional view showing a state where a ball grid array package is mounted on a conventional ball grid array package mounting substrate.

FIG. 6 is a side cross-sectional view showing a conventional solder ball and pad bonded state.

[Explanation of symbols]

 Reference Signs List 20 ball grid array package 22 I / O electrode 23 solder ball 25 solder bump 30 printed wiring board 31 insulating substrate 32 pad 33 lower layer pad 34 upper layer pad 35, 37 photoresist 36, 38 opening 39 recess

Claims (2)

[Claims] 1. A substrate having connection pads provided corresponding to solder balls of a ball grid array package, wherein a lower layer has a diameter larger than the diameter of the solder balls and an upper layer has a diameter substantially equal to the diameter of the solder balls. A connection pad having a diameter and formed in a terrace shape on the substrate;
A first solder resist formed on the substrate and having an opening having a diameter substantially equal to a diameter of a lower layer of the connection pad; and an opening having a diameter substantially equal to a diameter of the solder ball, and forming the opening with the first solder resist. A substrate for mounting a ball grid array package, comprising: a second solder resist formed on the first solder resist by aligning the openings of the solder resist coaxially. 2. The semiconductor device according to claim 1, wherein said first solder resist and said second solder resist have respective thicknesses of:
2. The substrate for mounting a ball grid array package according to claim 1, wherein the radius of the solder ball is approximately one half.