JP2008171879A - Printed circuit board and package mounting structure - Google Patents

Abstract

An underfill applied from the periphery of an LGA package soldered onto a printed circuit board is surely filled into a solder connection portion at the center of the package to enhance the reinforcement effect of the solder connection portion.
An LGA package is soldered around each PAD 2 for solder connection, which is disposed on the mounting surface of the LGA package of the printed circuit board 1 in correspondence with the connection terminals arranged in the area of the lower surface of the LGA package. By forming a groove 3 for accumulating flux in the solder paste that melts and flows out around the connection portion when electrically and mechanically connected, the flux is placed between the lower surface of the LGA package and the surface of the printed circuit board 1. The underfill applied from the periphery of the mounted LGA package after soldering is surely filled into the solder connection portion at the center of the package as well.
[Selection] Figure 1

Description

  The present invention relates to a technique for mounting an LSI package such as a BGA (Ball Grid Array) or an LGA (Land Grid Array) in which connection terminals are arranged in an area on a lower surface of a package on a printed circuit board.

  Corresponding to the recent trend toward downsizing and high functionality of electronic devices, in the mounting technology, development of technology for downsizing, thinning and high density of electronic components is required. In response to such demands, in the packaging technology, LSI packages, such as BGA (Ball Grid Array) and LGA (Land Grid Array), in which connection terminals are arranged in an area on the lower surface of the package are mainly used.

  There are various usage environments of electronic devices equipped with BGA and LGA, and in many cases, they are exposed to severe temperature environments. When an electronic device is subjected to thermal stress, a mechanically weakest solder joint may be distorted due to a difference in thermal expansion coefficient that varies depending on the structural material, which may lead to destruction. Further, in portable devices, destruction such as peeling of the solder connection portion is often caused by an impact at the time of dropping. Since such destruction becomes a fatal defect of the electronic device, an underfill is filled in the lower surface of the package as a reinforcement of the solder connection portion.

  However, in BGA with a reduced solder ball diameter or LGA without a solder ball, the gap between the package and the printed circuit board is narrow, so the residual flux in the molten solder paste often closes the gap, and penetration of the underfill The underfill may not be sufficiently filled in the solder connection portion. If the underfill is not sufficiently filled in the solder connection portion, the reinforcing effect is lowered, which causes a failure of an electronic device equipped with BGA or LGA.

  In particular, if the residual flux in the paste spreads out after the soldering is completed, the LGA package with a low solder height will be almost filled with the flux between the package and the printed circuit board. However, there is a problem that the flux interferes with the penetration of the underfill and the underfill is not filled up to the connection portion on the lower surface of the package.

  For this reason, conventionally, a method of removing the flux adhering to the gap formed between the chip component and the printed board in the soldering process by washing is generally performed.

  For example, Patent Document 1 discloses a technique for cleaning and removing residual solvent by forming small holes or slits for cleaning a residual solvent between mounting patterns of electronic components, and allowing a cleaning liquid to enter through these small holes or slits. In Patent Document 2, a gap is formed between the substrate and the stiffener on both sides of the chip soldered on the substrate, and the momentum is exerted when cleaning water is introduced from one of the gaps. A technique is described in which a cleaning effect is obtained by passing between the chip and the substrate while maintaining the same.

JP-A-6-232527 JP 2004-103996 A

  In the above prior art, it is necessary to provide a cleaning process for removing the flux adhered between the chip part and the printed board in the soldering process before injecting the underfill into the gap between the BGA chip part and the printed board. Therefore, there is a problem that the cost increases accordingly.

  In view of the above problems, an object of the present invention is to suppress adhesion of flux generated when soldering a BGA or LGA chip component onto a printed circuit board with a simple configuration in the gap between the chip part and the printed circuit board. Therefore, the underfill applied from the periphery of the LGA package soldered on the printed circuit board is surely filled into the solder connection portion at the center of the package, and a technique for enhancing the reinforcement effect of the solder connection portion is proposed. There is.

  Another object of the present invention is to provide a means that enables the cleaning process before underfill injection into the gap between the BGA chip component and the printed circuit board to be unnecessary or simple. The purpose is to reduce the manufacturing cost.

  The printed circuit board of the present invention is a printed circuit board in which a solder connection PAD connected to a solder ball of a BGA package or a PAD of an LGA package is disposed, and the solder connection is located near the solder connection PAD on the surface of the printed circuit board. In the solder paste that melts and flows out around the connection portion when the solder connection PAD and the solder ball of the BGA package or the PAD of the LGA package are electrically and mechanically connected by the solder paste applied to the PAD It is characterized by providing a groove for collecting the flux.

  The mounting structure of the BGA or LGA package of the present invention is such that the solder balls of the BGA package or the PAD of the LGA package are electrically and mechanically connected by the solder paste applied to the solder connecting PAD arranged on the printed circuit board. In a BGA or LGA package mounting structure in which an underfill is filled between the package lower surface and the printed circuit board, the solder is connected to the surface of the printed circuit board in the vicinity of the solder connection PAD. A groove for collecting flux that melts from the paste and flows out around the connection portion is formed.

  As the shape of the groove, it is formed as a circular groove surrounding the periphery of each solder connection PAD on the surface of the printed circuit board, or as a linear groove along the solder connection PAD arranged on the surface of the printed circuit board. be able to.

  In the present invention, it is possible to suppress the wetting and spreading of the flux by providing a groove for receiving the residual flux in the paste on the printed circuit board, so that the gap between the package lower surface and the printed circuit board is not blocked by the flux. It is possible to ensure filling of the underfill into the solder connection portion. Moreover, the penetration of the underfill into each solder connection part on the printed circuit board can be further improved by the groove.

  In the present invention, a groove is provided in the vicinity of each solder connection PAD provided on the surface of the printed circuit board to collect flux that melts and spreads around by heat treatment at the time of solder connection. The flux that is melted by the heat treatment can be stored in the groove, and the gap between the package and the printed circuit board is prevented from being blocked by the flux. Even in a mounting form in which the gap between them is narrow, it is possible to ensure filling of the solder connection portion with underfill, and to enhance the reinforcement effect of the solder connection portion in an electronic device equipped with BGA or LGA.

  Further, the flux that is melted by the heat treatment when the package is mounted on the printed circuit board is stored in a groove provided in the vicinity of each solder connection PAD of the printed circuit board, so that the gap between the package and the printed circuit board is blocked. Therefore, the cleaning process for removing the flux can be omitted or a simple cleaning process can be performed, and the manufacturing cost can be reduced accordingly.

  Also, since the underfill for filling easily penetrates between the package and the printed circuit board through this groove, it is possible to more efficiently fill the periphery of the PAD for solder connection with the underfill. The effect of further enhancing the reinforcement is also produced.

  FIG. 1 is a schematic diagram showing an LGA package mounting surface of a printed circuit board according to the first embodiment of the present invention and a cross section taken along line A-A ′.

  On the mounting surface of the LGA package of the printed circuit board 1, a solder connection PAD 2 is arranged corresponding to the connection terminals arranged in an area on the lower surface of the LGA package. In this embodiment, a groove 3 is formed in the vicinity of the PAD 2 for accumulating flux in the solder paste that melts and flows out around the connection portion when the LGA package is electrically and mechanically connected by solder. In FIG. 1, the groove 3 is formed as a groove that surrounds each PAD in a circular shape along the periphery of each solder connection PAD 2. At this time, if there is wiring from the PAD 2, the groove 3 is formed avoiding the lead wiring.

  As a method for forming the groove 3, the groove 3 is formed by employing an appropriate method such as a method in which the solder resist around the PAD of the printed circuit board 1 is set to an opening diameter larger than the PAD diameter, or a groove processing by a laser. be able to.

  FIG. 2 is a diagram illustrating a process of mounting the LAG package on the printed circuit board according to the present embodiment.

  When the LAG package is mounted on the printed circuit board according to the present embodiment, first, the upper surface of each PAD 2 of the printed circuit board 1 (FIG. 2A) in which the groove 3 is formed along the periphery of the PAD 2 for solder connection. Next, the solder paste 4 is applied (FIG. 2B), and then the connection PAD6 arranged in an area on the lower surface of the LGA package 5 and the PAD2 to which the solder paste 4 is applied are aligned. The LGA package 5 is mounted on the printed circuit board 1 and heat treatment is performed in this state.

  The solder paste 4 is melted by this heat treatment, and the PAD 6 of the LGA package 5 and the PAD 2 on the printed circuit board 1 are electrically and mechanically connected. At this time, the flux in the solder paste is also melted and the flux flows out around the solder connection portion. However, since the groove 3 is formed around the PAD 2, the flux that flows out around the connection portion enters the groove 3 around the PAD 2. It is induced and collected as the residual flux 7, and does not spread between the package 5 and the printed circuit board 1 (FIG. 2C).

  After soldering, the underfill 8 is applied from the periphery of the LGA package 5, and the underfill 8 is wetted and spread on the lower surface of the package to fill the solder connection portion (FIG. 3D). At this time, the flux 7 is accumulated in the groove 3 around the PAD 2 on the printed circuit board 1 and does not block the space between the LGA package 5 and the printed circuit board 1, so that the solder connection portion at the center of the package is surely underlined. Fill 8 is filled.

  As described above, according to this embodiment, when the LGA package 5 is mounted, the residual flux 7 in the molten solder paste is accumulated in the groove 3 due to the presence of the groove 3, and the gap between the LGA package 5 and the printed circuit board 1. It becomes possible to suppress spreading and getting wet. Since the residual flux 7 does not wet and spread, when the underfill 8 after the soldering is applied, the residual flux 7 is not hindered when the resin penetrates to the solder connection portion.

  In addition, since the groove 3 can be expected to induce the underfill 8 that has reached the vicinity of each solder connection portion to the solder connection portion, it also has an effect of improving the efficiency of filling the underfill into each solder connection portion. Therefore, the reinforcing effect of each solder connection portion can be further enhanced.

  FIG. 3 is a schematic view showing an LGA package mounting surface of a printed circuit board according to the second embodiment of the present invention.

  In the first embodiment, the grooves 3 for storing the flux are formed as grooves that surround each PAD in a circle along the periphery of each solder connection PAD 2. In this embodiment, as shown in FIG. In addition, the groove 3 for storing the flux is formed linearly along each row of the PAD 2.

  Also in the present embodiment, as in the first embodiment, the PAD 6 of the LGA package 5 and the PAD 2 on the printed circuit board 1 are melted during the heat treatment for electrically and mechanically connecting the solder connection portion and the periphery thereof. The flux in the solder paste 4 flowing out is guided to the groove 3 on the printed circuit board 1 formed linearly along each row of the PAD 2 and can be accumulated in the groove 3 as the residual flux 7. And the printed board 1 are not wetted and spread.

  Therefore, when the underfill 8 is applied from the periphery of the LGA package 5 after soldering and wetted and spread on the lower surface of the package to fill the solder connection portion, the underfill 8 is not obstructed by the residual flux 7 and is not obstructed by the LGA package 5. It is possible to infiltrate and fill the solder connecting portion at the center of the core, and a sufficient reinforcing effect of the solder connecting portion can be obtained.

  In the case of this embodiment, the grooves 3 for accumulating the flux are formed linearly along each row of the PADs 2. Therefore, the grooves 3 can be formed by using a solder resist of the printed circuit board 1 or a laser. In addition to the groove processing, a forming method by dicing can also be adopted, and the forming method of the groove 3 is relatively easy, and the cost can be further reduced.

  Further, the linear groove 3 is provided so as to extend slightly outside the range of the LGA package 5 mounting surface of the printed circuit board 1, so that when the underfill 8 is applied from the periphery of the LGA package 5, The fill 8 is guided to the linear groove 3 and easily penetrates into the surface of the printed circuit board 1 where the LGA package 5 is mounted, and an effect of further increasing the underfill filling efficiency to the solder connection portion can be expected.

  In the above-described embodiment, as the shape of the groove formed on the printed board, the circular groove surrounding each solder connecting PAD peripheral part on the printed board and the solder connecting PAD arranged on the printed board are used. However, the shape of the groove is not limited to the above-described embodiment, and can be provided in an arbitrary shape in the vicinity of the solder connection PAD on the printed board. At that time, if wiring is routed from the PAD 2, a groove is formed avoiding the wiring for routing.

It is the schematic which shows the LGA package mounting surface of the printed circuit board in the 1st Embodiment of this invention, and a cross section. It is a figure which shows the LAG package mounting process to the printed circuit board of this embodiment. It is the schematic which shows the LGA package mounting surface of the printed circuit board in the 2nd Embodiment of this invention.

Explanation of symbols

1 Printed circuit board 2 PAD for solder connection
3 Groove 4 Solder paste 5 LAG package 6 LAD package PAD
7 Residual flux 8 Underfill

Claims (6)

In a printed circuit board in which a solder connection PAD connected to a solder ball of a BGA package or a PAD of an LGA package is arranged,
In the vicinity of the solder connection PAD on the surface of the printed circuit board, the solder connection PAD and the solder ball of the BGA package or the PAD of the LGA package are electrically and mechanically connected by a solder paste applied to the solder connection PAD. A printed circuit board provided with a groove for accumulating flux in the solder paste that melts and flows out around the connecting portion when connected to the connector.   2. The printed circuit board according to claim 1, wherein the groove is formed as a circular groove surrounding a periphery of each solder connection PAD on the printed circuit board.   The printed circuit board according to claim 1, wherein the groove is formed as a linear groove along the solder connecting PAD arranged on the printed circuit board. The solder balls of the BGA package or the PAD of the LGA package are electrically and mechanically connected by the solder paste applied to the solder connection PAD arranged on the printed circuit board, and between the lower surface of the package and the printed circuit board. In a BGA or LGA package mounting structure filled with underfill,
A BGA or LGA package characterized in that a groove is formed near the solder connection PAD on the surface of the printed circuit board for collecting flux that melts from the solder paste and flows out to the periphery of the connection portion during the connection. Implementation structure.   5. The mounting structure for a BGA or LGA package according to claim 4, wherein the groove is formed as a circular groove surrounding the periphery of each solder connection PAD on the printed circuit board. 5. The mounting structure of a BGA or LGA package according to claim 4, wherein the groove is formed as a linear groove along the solder connection PAD arranged on the printed circuit board.

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