WO2008004288A1

WO2008004288A1 - Printed wiring board and electronic device

Info

Publication number: WO2008004288A1
Application number: PCT/JP2006/313405
Authority: WO
Inventors: Mitsuhiko Sugane
Original assignee: Fujitsu Limited
Priority date: 2006-07-05
Filing date: 2006-07-05
Publication date: 2008-01-10

Abstract

A printed wiring board, which is constituted to be mounted with a surface mount component, has a first land to which a wiring is connected and a second land to which no wiring is connected. The second land has a lager area than the first land, and the closely contacted area of the second land is larger than that of the first land. The outer peripheral portion other than the central portion of the second land may be covered with a resist.

Description

Specification

Printed wiring board and electronic device

Technical field

TECHNICAL FIELD [0001] The present invention relates to a printed wiring board, and more particularly to a printed wiring board on which a surface land for mounting a surface mounting component is formed and an electronic device using such a printed wiring board.

Background art

[0002] A multi-layer printed wiring board used in an electronic device is often formed with a large number of lands for mounting surface mounting components. Ordinary lands are shaped based on commonly used wiring specifications. The land shape is generally circular, and a pattern wiring with a width much smaller than the land diameter is connected to one part of the land circumference.

[0003] Surface mount components may include terminals that do not need to be electrically connected, and no wiring is connected on the printed wiring board to lands to which such terminals are connected. In other words, a land to which a terminal that does not need to be electrically connected is connected is an isolated land on the printed wiring board. Such an isolated land is generally referred to as an “empty pin land”.

[0004] When a component for surface mounting mounted on a printed wiring board fails, the component may be replaced. When replacing a part, the joining member such as solder that joins the terminal and land of the part is heated and melted. At this time, thermal stress is applied between the land and the substrate of the printed wiring board. Unlike normal lands, empty pin lands are not connected to the pattern wiring, so the adhesion of the printed wiring board to the substrate is small. For this reason, the vacant pin land is more easily peeled off than the normal land due to the thermal stress applied during component replacement. In particular, when the molten solder remaining on the land after removing the surface mounting components is scraped off with a soldering iron or the like, the unused pin land may peel off.

[0005] In addition, in a land to which normal wiring is connected, when a surface mounting component is mounted, an external force may be applied to a connection portion with a terminal located around the surface mounting component. Thermal stress may be applied due to heat generated during the operation of surface mount components. Therefore, it is preferable to take measures to prevent the separation of the terminals located in the peripheral portion of the surface mount component.

[0006] Various techniques have been proposed to prevent normal lands from peeling off or falling off. For example, a technique has been proposed in which through holes are provided in the pattern wiring in the vicinity of the land to release heat and reduce the thermal stress (see, for example, Patent Document 1). A technique has been proposed in which through holes connected to the formed lands are formed to prevent the lands from falling off the substrate cover (see, for example, Patent Document 2). ₀ Further, lead wires for fixing electronic components are provided. A technique for forming a through hole in a land in which a mounting hole to be inserted is formed has been proposed (for example, refer to Patent Document 3). ₀ Also, a land having a through hole through which an electronic component lead is inserted. A non-penetrating via hole is formed inside

A technique for increasing the contact area between the through-hole land portion and the substrate has been proposed (for example, see Patent Document 4).

Patent Document 1: Japanese Patent Laid-Open No. 3-6088

Patent Document 2: Japanese Utility Model Publication No. 7-3161

Patent Document 3: Japanese Patent Laid-Open No. 11-8443

Patent Document 4: Japanese Unexamined Patent Application Publication No. 2004-172329

Disclosure of the invention

Problems to be solved by the invention

[0007] The above-described prior art is a technique for reducing the thermal stress of a normal land or improving the adhesion, and has not been particularly effective in consideration of the problem of detachment of an empty pin land. Since the empty pin land is not connected to the pattern wiring, it easily peels off from the normal land. Therefore, a countermeasure for preventing the empty pin land from being peeled off is particularly desired. In addition, even for ordinary lands, it is desirable to take measures to prevent the lands connected to the terminals located in the peripheral portion of the surface mount component from being peeled off.

Means for solving the problem

[0008] A general object of the present invention is to provide a novel and useful printed wiring board and electronic device by solving the above-described problems. [0009] A more specific object of the present invention is to provide a printed wiring board in which normal lands and vacant pin lands are prevented from being separated from the printed wiring board by thermal stress. The

In order to achieve the above-described object, according to the present invention, a printed wiring board configured to be mounted with a surface mounting component, the first land to which the wiring is connected, and the wiring And a second land that is not connected, and the second land has a larger area than the first land.

[0011] The printed wiring board according to the present invention is preferably covered with an outer peripheral force S resist other than the central portion of the second land. A through via may be connected to the second land. In addition, the second land may have at least one elongated, reinforcing portion extending radially from the periphery!

According to another aspect of the present invention, an electronic device having the above-described printed wiring board is provided.

[0013] Other objects, features and advantages of the present invention will become more apparent upon reading the following detailed description with reference to the accompanying drawings.

The invention's effect

[0014] According to the present invention, the first land corresponds to a normal land, and since the second land, which is difficult to peel off because it is connected to the wiring, is used as an empty pin land, Since the area is larger, the contact area is large, and peeling becomes difficult. Therefore, it is possible to prevent the vacant pin land from peeling off.

Brief Description of Drawings

FIG. 1 is a perspective view of an electronic device incorporating a printed wiring board to which the present invention is applicable.

FIG. 2A is a plan view of a part of the printed wiring board according to the first embodiment of the present invention.

2B is a cross-sectional view taken along the line II of the printed wiring board shown in FIG. 2A.

FIG. 3A is a plan view of an elliptical empty pin land.

FIG. 3B is a plan view of a star-shaped empty pin land.

FIG. 3C is a plan view of an empty octagon land land.

FIG. 3D is a plan view of a diamond-shaped empty pin land.

FIG. 3E is a plan view of an inverted heart-shaped empty pin land. FIG. 4A is a plan view of a part of a printed wiring board according to a second embodiment of the present invention.

4B is a cross-sectional view taken along line VI-VI of the printed wiring board shown in FIG. 4A.

FIG. 5A is a plan view of a part of a printed wiring board according to a third embodiment of the present invention.

5B is a cross-sectional view taken along the line VV of the printed wiring board shown in FIG. 5A.

FIG. 6 is a graph showing the results of a peeling test.

Explanation of symbols

[0016] 1 server

10, 20, 30, 40

12 Board module

14 Surface mount parts

22 rand

24 Wiring

26 Solder resist

26a, 26b opening

28, 28A, 28B Unused pin land

32 Through-via

42 Reinforcement

BEST MODE FOR CARRYING OUT THE INVENTION

Next, embodiments of the present invention will be described with reference to the drawings.

The present invention is applied to a printed wiring board used in an electronic device. FIG. 1 is a perspective view of a server 1 which is an example of an electronic apparatus in which a printed wiring board 10 to which the present invention is applicable is incorporated. In the server 1, a board module 12 to which a large number of printed wiring boards 10 are connected is incorporated. Each printed wiring board 10 is provided with a large number of surface mounting components 14 such as BGA type LSIs.

A first embodiment of the present invention will be described with reference to FIGS. 2A and 2B. 2A is a plan view showing a part of the printed wiring board 20 according to the first embodiment of the present invention, and FIG. 2B is a cross-sectional view taken along the line II of the printed wiring board shown in FIG. 2A. The printed wiring board 20 is a multilayer board, wiring is also formed in the inner layer, and the wiring is connected by via holes or the like. In FIG. 2B, portions other than the surface portion of the printed wiring board 20 are shown in a simplified manner.

A circular land 22 for mounting a surface mounting component is formed on the surface of the printed wiring board 20, and a wiring 24 is connected to the land 22. For example, the land 22 and the wiring 24 are formed simultaneously in a process of patterning a copper foil by etching or the like. A solder resist 26 is provided on the surface of the printed wiring board 20 to protect the wiring 24 while leaving a portion where the land 22 is formed. In the portion where the land 22 is formed, the solder resist 26 is removed to form a circular opening 26a. That is, the land 22 is exposed in the opening 26a, and the terminal of the surface mounting component can be soldered to the land 22.

On the printed wiring board 20, in addition to the normal circular land 22 described above, an empty pin land 28 to which no wiring is connected is formed. The empty pin land 28 has a shape other than a circle (in the example shown in FIG. 2A, an oval shape), and is formed so that the outer shape is larger than the outer shape of the land 22. A circular opening 26b having the same dimensions as the circular land 22 is formed in the solder resist 26 provided on the vacant pin land 28. In this opening 26b, the empty pin land 28 is exposed, and the terminal of the surface mounting component can be soldered to the empty pin land 28.

[0022] In the portion other than the opening 26b, the empty pin land 28 is covered with the solder resist 26. Therefore, for example, even when the portion of the empty pin land 28 is rubbed with a soldering iron or the like, the empty pin land 28 in which the soldering iron does not directly contact the edge of the empty pin land 28 is difficult to peel off. Natsume.

[0023] Further, since the empty pin land 28 has a larger shape than the normal land 22, that is, has a larger area, the contact area of the empty pin land 28 is larger than that of the normal land 22. It is difficult to peel off. In order to increase the contact area, it is preferable to make the vacant pin land 28 large enough not to contact the surrounding wiring 24 or land 22. The shapes of the vacant pin lands 28 can be considered as shown in Fig. 3, but are not limited to these shapes.

[0024] FIG. 3A shows an oval free pin land 28, and only the center portion of the oval is An opening 26b of the resist 26 is formed. FIG. 3B shows a star-shaped vacant pin land 28, and the opening 26b of the solder resist 26 is formed only in the central portion of the star. FIG. 3C shows an octagonal empty pin land 28, and the opening 26b of the solder resist 26 is formed only in the central portion of the octagon. Fig. 3D shows an empty pin land 28 of a diamond shape, and an opening 26b of the solder resist 26 is formed only in the central portion of the diamond shape. FIG. 3E shows an inverted heart-shaped empty pin land 28, and the opening 26b of the solder resist 26 is formed only in the center portion of the inverted heart shape. That is, the empty pin land 28 can be one of an ellipse, a star, a polygon, and a heart.

Next, a second embodiment of the present invention will be described with reference to FIGS. 4A and 4B. 4A is a plan view showing a part of the printed wiring board 30 according to the second embodiment of the present invention, and FIG. 4B is a cross-sectional view taken along the line IV-IV of the printed wiring board shown in FIG. 4A. 4A and 4B, parts that are the same as the parts shown in FIGS. 2A and 2B are given the same reference numerals, and descriptions thereof are omitted.

[0026] The printed wiring board 30 is a multilayer board, wiring is also formed in the inner layers, and the wiring is connected by via holes or the like. In FIG. 4B, portions other than the surface portion of the printed wiring board 30 are shown in a simplified manner.

The empty pin land 28A according to the present embodiment has the same configuration as the empty pin land 28 according to the first embodiment described above, but is different in that the through via 32 is connected. The through via 32 is formed in a portion of the vacant pin land 28 </ b> A covered with the solder resist 26. The through via 28A is a force that extends through the printed wiring board 30 to the back surface so that it is not electrically connected to other lands and wiring, and the land 28A for the empty pin is in an electrically isolated state To be kept.

[0028] By connecting the through via 32, the adhesion of the empty pin land 28 can be further increased, and peeling of the empty pin land 28 can be prevented.

[0029] The shape of the empty pin land 28A in which the through via 32 is provided is not limited to the elliptical shape shown in FIG. 4B, and may be various shapes including the shapes shown in FIGS. 3A to 3E. In addition, if there is a place where the number of through vias 28 is not limited to one, a plurality of through vias may be provided in one empty pin land. Next, a third embodiment of the present invention will be described with reference to FIGS. 5A and 5B. FIG. 5A is a plan view showing a part of the printed wiring board 40 according to the third embodiment of the present invention. 5A and 5B, parts that are the same as the parts shown in FIGS. 2A and 2B are given the same reference numerals, and descriptions thereof are omitted.

[0031] The empty pin land 28B according to the present embodiment is a circular shape having the same shape as that of the normal land 22, and is different in that the reinforcing portion 42 extends in the force and peripheral force. The reinforcing portion 42 is formed at a position so as not to contact the land 22 and the wiring 24 around the empty pin land 28B. In this embodiment, the reinforcing portion 42 is formed as an elongated pattern having the same width as the wiring 24. By using the same dimensions as the wiring 24, the same design rules as the wiring 24 can be applied. However, the width of the reinforcing portion 42 may be larger than the wiring 24. Further, the number of the reinforcing portions 42 is not limited to one, and two reinforcing portions may be configured to extend in opposite directions from both sides of the empty pin land 28B, and configured to extend in three directions in a Y shape. Even so.

[0032] By forming the reinforcing part 42 so that the force of the empty pin land 28B extends to the periphery, the contact area of the empty pin land 28B is increased, and peeling of the empty pin land 28B is prevented. It is out.

[0033] The present inventor created vacant pin lands 28B having various reinforcing portions 42 and conducted a peeling test. Figure 6 is a graph showing the results of the peel test. The shape of the empty pin land is shown at the top of the graph.

[0034] As a sample for the peeling test, the following empty pin lands were formed.

[0035] 1) Sample 1: Land for vacant pins without a reinforcing part

2) Sample 2: Thicker than ordinary wiring extending in one direction!

3) Sample 3: Land for vacant pins with reinforcing parts wider and wider than normal wiring extending in two directions on a straight line

4) Sample 4: Land for vacant pin with reinforcement part thicker and wider than normal wiring extending in two directions in L shape

5) Sample 5: Land for hollow pin with reinforcing part wider and wider than normal wiring extending in 3 directions in Y shape 6) Sample 6: Land for vacant pins with a reinforcing part of the same width as normal wiring extending in one direction

7) Sample 7: Land for vacant pins that has a reinforcing part with the same width as a normal wire extending in two directions on a straight line

8) Sample 8: Land for vacant pins with reinforcement part of the same width as normal wiring extending in two directions in L shape

As a result of creating a plurality of the above samples and conducting a peel test, the results shown in Fig. 6 were obtained.

[0036] Sample 1 is an independent land having no reinforcement, and was tested as a comparison target. The load required for peeling off Sample 1 was about 1400 g to 1900 g. In Sample 2, the load required for the peel force S was 1600g to 2700g, which was about 500g larger than Sample 1 on average. As a result, it was confirmed that it was difficult to peel off the empty pin land by providing the reinforcing portion.

[0037] In Sampnore 3, the load required for the peeling force S was 2100g to 3200g, which was about 1OOOg larger than Sample 1 on average. It was confirmed that it would be more difficult to peel off by providing reinforcing parts on both sides. Therefore, as a result of testing Sample 4, it was found that the load required for peeling was 2000 g to 2500 g, which was not much different from Sample 1 having one reinforcing part. As a result, it was found that if two reinforcing parts were provided, it would be effective to extend in opposite directions on both sides of the empty pin land as in Sample 3.

[0038] Next, as a result of testing Sample 5, the load required for peeling was 2700 g to 4300 g, and it was found that the load did not peel up to twice that of Sample 1 on average. As shown in Sample 5, it was confirmed that the effect of preventing delamination was dramatically improved by providing three reinforcing parts extending in three directions at equal angular intervals.

[0039] Sample 6 has the same configuration as sample 2, but with a thinner reinforcing portion. Sample 7 has the same configuration as Sample 3 with a thinner reinforcement. In addition, Sample 8 has the same configuration as Sample 4 with a thinner reinforcing portion. For samples 6-8, the load required for peeling was compared to the load required for peeling for samples 2-4. Although the variation was large, the average value was almost the same. From this result, it was proved that the width of the reinforcement did not affect the peeling load.

[0040] From the results of the peeling test as described above, the width of the reinforcing portion is equal to the width of the normal wiring. By extending the three reinforcing portions in three directions at equal angular intervals, the land for empty pins It was found that it was possible to effectively prevent peeling. Note that the width of the reinforcing portion is not limited to the width of the wiring, and can be any width.

[0041] Although the above-described embodiment is a configuration for preventing the separation of the land for the empty pin, the configuration of the above-described embodiment may be applied to a normal land to which wiring is connected to prevent the separation. it can. For example, the above-mentioned reinforcing portion may be provided for a land that is easily peeled out of normal lands. Lands connected to terminals located on the corners and outer periphery of surface mount components may be more easily peeled off than lands connected to terminals located on the inner periphery where external forces are more likely to act. There is. Therefore, as in the above-described embodiment, by providing a reinforcing portion having the same width as the wiring, the adhesion area can be increased and peeling can be prevented. Since the reinforcement part is not connected to other lands or wiring, the function as a land is not impaired. In addition, the reinforcing part can be designed with the same design rule as the wiring, so that the land having the reinforcing part can be designed in the same way as a normal land or wiring design.

Industrial applicability

The present invention can be applied to an electronic device in which a printed wiring board is incorporated.

Claims

The scope of the claims

[1] A printed wiring board configured to be mounted with a surface mounting component,

A first land to which the wiring is connected;

No wiring is connected, with the ^second land

Have

The second land has a larger area than the first land.

[2] The printed wiring board according to claim 1,

A printed wiring board, wherein an outer peripheral portion other than a central portion of the second land is covered with a resist.

[3] The printed wiring board according to claim 2,

The printed wiring board, wherein a shape of the second land portion not covered with the resist is substantially equal to the shape of the first land.

[4] The printed wiring board according to claim 1,

The printed wiring board, wherein the first land has a circular shape, and the second land has a shape other than a circle including the shape of the first land.

[5] The printed wiring board according to claim 4,

The printed wiring board according to claim 2, wherein the second land has one of an ellipse, a star, a polygon, and a heart shape.

[6] The printed wiring board according to claim 1,

A printed wiring board, wherein a through via is connected to the second land.

[7] The printed wiring board according to claim 6,

The outer peripheral portion other than the central portion of the second land is covered with a resist, and the shape of the portion of the second land not covered with the resist is substantially equal to the shape of the first land. The printed wiring board, wherein the via is provided in a portion other than the second land portion that is not covered with the resist.

[8] The printed wiring board according to claim 1,

The second land has at least one elongated reinforcement extending radially from its periphery. A printed wiring board having a portion.

[9] The printed wiring board according to claim 8,

A width of the reinforcing portion is the same as the width of the wiring.

[10] The printed wiring board according to claim 8,

The printed circuit board according to claim 2, wherein the second land has three reinforcing portions, and the reinforcing portions extend in three directions at equal angular intervals.

[11] The printed wiring board according to claim 8,

The printed wiring board, wherein the reinforcing portion extends to a portion where the first land and the wiring are not provided.

[12] A printed wiring board configured to be mounted with a surface mounting component,

A printed wiring board comprising: a land to which wiring is connected, and at least one of the lands has at least one elongated reinforcing portion extending radially from a peripheral edge thereof.

[13] The printed wiring board according to claim 12,

A width of the reinforcing portion is the same as the width of the wiring.

[14] The printed wiring board according to claim 12,

The printed wiring board, wherein the reinforcing portion extends to a portion where the land and the wiring are not provided.

[15] The printed wiring board according to claim 12,

Among the lands, the land provided with the reinforcing portion is a land configured to be connected to a terminal located on an outer peripheral portion of the surface mounting component.

16. An electronic device having the printed wiring board according to any one of claims 1 to 15.