JPH0927666A - Mounting structure of chip component on wiring board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a mounting structure of a chip component on a wiring board, wherein adjacent lands are protected against a short circuit caused by a solder layer when chips are mounted high in mounting density, and connection failures caused by a shortage of solder can be eliminated. SOLUTION: A land 1 is composed of an island-like land 1a and a thin land 1b, and the lands 1 are arranged so as to dispose the adjacent lands 1a and 1b zigzag, a cream solder layer 4 is formed in the region of the island-like land 1a by printing, and the lead terminals 8 of chip components which are arranged in parallel are placed on the cream solder layers 4 arranged zigzag and soldered.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a chip component mounting structure suitable for high-density mounting of chip components, and more specifically, a lead floating due to a short circuit between adjacent land portions or insufficient solder to the land portions. The present invention relates to a chip component mounting structure for preventing the above problems.

[0002]

2. Description of the Related Art FIG. 9 shows a perspective view of a land portion of a wiring board in high-density mounting of chip parts and a screen for printing solder on the land portion, and FIG. 10 shows an integrated circuit or the like on the land portion. The perspective view of the state which mounted the lead terminal of a chip component is shown.

The land portions 10, which are a part of the wiring pattern of a wiring board (not shown), have a rectangular shape and are closely arranged at intervals L in a parallel state. The screen 11 on which the cream solder layer is printed and formed on these lands 10 has an opening 12 having a size substantially corresponding to the shape of each land, and the cream solder is spread over the area of each land 10 through the opening 12. The layer 13 is printed.

Thus, with the lead terminals 14 of the chip component mounted on the cream solder layer 13 printed on the ride portion 10 as shown in FIG. 10, the cream solder layer 13 is transported into the reflow oven. Is melted and the land portion 10 and the lead terminal 14 of the chip component are soldered.

By the way, there is a problem as described below in the printing state of the land portion and the cream solder layer as described above.

FIG. 11a shows a state in which the cream solder layer 13 is printed at the correct position on each land portion 10. At this time, the cream solder layer 13 retains its shape.
FIG. 11b shows the case of being transferred into the reflow furnace and first preheated.
As shown in FIG. 3, the cream solder layer 13 melts and the land portion 1
A phenomenon that spreads around 0 occurs. Therefore, there is a high risk that the cream solder layers 13, 13 of the adjacent land portions 10 contact each other. When the cream solder layer 13 spread around the land portion 10 due to melting passes through the reflow oven and is cooled, the surface tension generated between the cream solder layer 13 and the lead terminal causes the cream solder layer 13 to contract again into the area of the land portion.

On the other hand, FIG. 12a shows a state in which the cream solder layer 13 is deviated and printed on each land portion 10. In this case, when the cream solder layer 13 is conveyed in the reflow and preheated, as shown in FIG. Causes a defect that the adjacent land portions 10 are largely overlapped with each other and the adjacent land portions 10, 10 are short-circuited.

The state of such defects will be described in more detail with reference to FIG. 13. FIG. 13A shows a state in which the cream solder layer 13 is printed on the land portion 10, and the cream solder layer 13 is the opening portion of the screen. Although the shape is maintained along the shape of, when the cream solder layer 13 is preheated,
As shown in FIG. 13 b, a so-called “drip” is generated in the cream solder layer and melts in the shape of a mountain, and the cream solder layer 1
3,13 will contact each other.

However, when the contact ratio of the cream solder layer is increased or the cream solder layers are largely overlapped from the state of FIG. 13b described above, the land portions 10, 10 are solder layers 13 as shown in FIG. 13c. When a short circuit occurs in the form of a bridge, or when the solder layer shrinks as shown in FIG. 13d, the solder layer largely moves to one land portion side, and the solder layer on the other land portion is extremely reduced. Defects that cause solder shortage occur. Here, the ideal soldering state of the lead terminal 14 is as shown in FIG. 14a, but if the solder layer is reduced, it may cause connection failure such as floating of the lead terminal as shown in FIG. 14b.

Therefore, as a conventional example in which the above-mentioned defects are avoided, there is one as shown in FIGS. In this case, the land portions 10 have a rectangular shape as described with reference to FIG. 9, and are closely arranged in a parallel state at intervals L. The opening portion 1 of the screen 11 is provided on each land portion 10.
5, the cream solder layer 16 having a predetermined shape is printed and formed in a zigzag pattern. FIG. 17 shows a state in which the lead terminals 14 of the chip component are mounted on the zigzag cream solder layer 17. The cream solder layer 16 has a size slightly protruding from the width of the land portion 10. This is to ensure that a necessary amount of solder layer can be secured in the originally printed land portion even if the solder layer spreads over the surface of the land portion 10 to some extent during melting.

In the improved conventional example having such a structure, FIG. 18A shows that the cream solder layer 16 is formed on each land portion 10.
Is printed in the correct position, and when the cream solder layer 16 is conveyed into the reflow oven and preheated first, the cream solder layer 16 melts and spreads around the land portion 10 as shown in FIG. 18b. But adjacent cream solder layer 1
6, 16 or the cream solder layer 16 and the land portion 1
There is no danger of contact with zero.

On the other hand, FIG. 19a shows a state in which the cream solder layer 16 is deviated and printed on each land portion 10. In this case, when the cream solder layer 16 is conveyed in the reflow and preheated, as shown in FIG. It is inevitable that the adjacent land portions 10 and 10 overlap each other and short-circuit between the adjacent land portions 10, 10.

The present invention has been made to solve the above-mentioned problems, and effectively eliminates a short circuit between adjacent lands due to a solder layer and a connection failure due to insufficient solder in high-density mounting of chip components. An object of the present invention is to obtain a chip component mounting structure on a wiring board that can be manufactured.

[0014]

In order to achieve the above-mentioned object, a chip component mounting structure according to the present invention has a lead terminal of a chip component on a land portion of a wiring pattern printed and formed on a wiring board via a solder layer. In a high-density chip component mounting structure, adjacent lands are arranged in a staggered pattern, solder layers are also printed in a staggered pattern on the lands, and chip components are arranged in parallel on each solder layer. These lead terminals are mounted and soldered.

In the chip component mounting structure of the present invention configured as described above, the adjacent land portions are arranged in a zigzag pattern, and the solder layers on the land portions are also printed in a zigzag pattern along the land portions. , Even if the solder layer is printed with a slight deviation from the land portion, even if the solder layer is melted and spread by preheating, there is no contact with the adjacent land portion or the adjacent solder layer, Short circuits between them can be avoided.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of a chip component mounting structure according to the present invention will be described below by taking a lead terminal mounting structure of an integrated circuit (for example, LSI) as an example.

FIG. 1 shows a land portion of a wiring board according to this embodiment,
FIG. 2 is a perspective view of a screen for printing the cream solder layer, and FIG. 2 is a plan view of one land portion with the cream solder layer printed on the land portion.

In FIG. 1, the land portions 1 closely arranged in parallel in a pitch are composed of an island-shaped land portion 1a and a thin land portion 1b in a part thereof, and each land portion 1 is an adjacent island. -Shaped lands 1a and thin lands 1b are alternately arranged in a zigzag pattern, and the thin lands 1b are conductively connected to a wiring pattern of a wiring board (not shown).

On the screen 2 on which the cream solder layer is printed and formed on each of the land portions 1, openings 3 similarly arranged in a zigzag pattern are formed at positions corresponding to the island-shaped land portions 1a arranged in a zigzag pattern. The cream solder layer is printed on the island-shaped land portions 1a of each land portion 1 through the openings 3. That is, the cream solder layers are also arranged in a zigzag pattern together with the island-shaped lands 1a. Land part 1
FIG. 2 shows a state in which the cream solder layer is printed on, and the white portion is the cream solder layer 4. This cream solder layer 4
Is substantially the same shape as the island-shaped land portion 1a,
It is contained within the area of the land 1a. That is, the island-shaped land portion 1a has a narrow land portion 1 of the adjacent land portion 1.
b is adjacent to each other, and the narrow land portion 1b is adjacent to the island-shaped land portion 1a of the adjacent land portion 1. Therefore, the distance between the adjacent land portions 1 and 1 is the same as in the conventional example shown in FIGS. As described above, even if the distance is L, the space can be substantially widened as the distance L ₀ as shown in FIG.

As an example of printing the cream solder layer 4 on the land portion 1, as shown in FIG. 3, a supporting member 5 having high plane accuracy is used.
By placing the wiring board 6 on the wiring board 6 and supplying the solder paste which is the cream solder 4 with the squeegee 7 from the top of the screen 2 stacked on the wiring board 6, the solder paste is accumulated in the opening 3 of the screen 2, The cream solder layer 4 can be printed on the so-called island-shaped land portion 1a.

FIG. 4 is a perspective view showing a state in which the lead terminals 8 of the integrated circuit are mounted on the cream solder layer 4 of each land 1.

The lead terminals 8 are aligned in parallel, and therefore, when the lead terminals 8 are mounted on the cream solder layer 4 arranged in a staggered pattern, the lead terminals 8 are arranged.
There is a case where the base portion 8a side contacts the cream solder layer 4 and a case where the tip portion 8b side of the lead terminal 8 contacts the cream solder layer 4.

Now, with reference to FIGS. 5 and 6, a description will be given of the state when the cream solder layer 4 is “drooped” by preheating in the reflow furnace. The lead terminals are omitted in the figure.

FIG. 5a shows a state in which the cream solder layer 4 is printed at the correct position on the island-shaped land portion 1a. When the cream solder layer 4 is conveyed into the reflow oven and preheated first, the cream solder layer 4 is changed to the state shown in FIG. 5b. As shown, the cream solder layer 4 melts and spreads around the island-shaped land portion 1a, but the adjacent cream solder layers 4 and 4 or the melted cream solder layer 4 and the adjacent thin land portion 1b come into contact with each other. There is no danger.

On the other hand, FIG. 6a shows a state in which the cream solder layer 4 is deviated and printed on the island-shaped land portion 1a. Even in this case, when the cream solder layer 4 is conveyed in the reflow and preheated, as shown in FIG. Although the layer 4 melts and spreads around it, neither the adjacent cream solder layers 4, 4 nor the melted cream solder layer 4 and the adjacent thin land portion 1b come into contact with each other.

As described above, according to the present invention, the island-shaped land portions 1a of the land portion 1 are arranged in a staggered manner, and the cream solder layer 4 is printed in a staggered manner on the island-shaped land portions 1a. As a result, the space between the lands 1 and 1 can be substantially widened, and there is a danger that the melted cream solder layer 4 will contact the adjacent lands 1 or the melted solder layers. Can be resolved. As a result, adjacent lands become short-circuited in the solder layer due to a bridge state, and when the cream solder layer is cooled, the solder layer is transferred to one of the lands a lot, resulting in insufficient solder and solder defects such as floating feet. There is an advantage that such a thing can be avoided.

FIGS. 7a and 7b show the lead terminals 8 soldered. FIG. 7a shows a soldering state when the tip portion 8b side of the lead terminal 8 is in contact with the cream solder layer 4 as described in FIG. 4, and FIG. 7b shows the base portion 8a side of the lead terminal 8 on the cream solder layer 4. This is the soldering state when they are in contact.

Ideally, as shown in FIG. 14a, it is preferable that the tip end side and the base side of the lead terminal 8 are soldered with a sufficient amount of solder, but a chip component as a mounting component has multiple terminals. Therefore, the mechanical strength expected for one terminal is somewhat lower, but the mechanical strength is improved as compared with the case of insufficient solder shown in FIG. 14b, and the reliability of the entire terminal is high.

Further, according to the present invention, the island-shaped land portions 1a of the land portion 1 are arranged in a staggered manner, and the cream solder layer 4 is printed in a staggered manner on the island-shaped land portions 1a. The arrangement is such that the space between the adjacent land portions 1 can be secured most, and as a result, it is possible to deal with a case where the cream solder layer is slightly misaligned with the land portion. Therefore, it can be used even if the precision of the screen printing machine is not so high.

As another advantage, it is possible to further reduce the distance between the lands, so that high density mounting of chip components becomes possible.

Further, the land portion of the present invention has a smaller land area than that of the conventional improvement example described in FIG.
Moreover, since the amount of solder can be reduced, the width direction of the opening 3 of the screen 2 can be further narrowed, and the bridge prevention effect by cream solder can be further improved.

The present invention is not limited to the embodiment described above and shown in the drawings, and various modifications can be made without departing from the scope of the invention.

FIG. 8a shows another embodiment of the land portion of the present invention, which is an example in which only the island-shaped land portions 1a shown in FIG. 1 are arranged in a staggered manner, and FIG. 8b shows 8C shows an example in which the island-shaped land portions 1a are arranged in a rectangular shape and arranged in a staggered pattern. FIG. 8C shows an example in which the island-shaped land portions 1a are formed in a round shape. Further, FIG. 8D shows a flat land portion 1a. This is an example of a triangular shape. In any case, the cream solder is printed so as to fit within the area of each land.

Further, in the embodiment, an LSI is used as a chip component.
Although the case where a multi-terminal lead terminal of an integrated circuit such as the above is mounted has been described, the present invention is also widely applicable to a case where a single-terminal chip component is mounted at high density.

[0035]

As described above, in the chip component mounting structure of the present invention, the adjacent land portions are arranged in a zigzag pattern, and the solder layers are also printed in a zigzag pattern on the land portions. Therefore, it becomes possible to substantially widen the gap between the lands, and it is possible to eliminate the risk of the molten cream solder layer contacting the adjacent lands or the molten solder layers. There is an effect that it is possible to prevent a portion from becoming a bridge state in the solder layer and short-circuiting, or a soldering defect such as a floating foot of a lead terminal due to an insufficient amount of solder.

[Brief description of drawings]

FIG. 1 is a perspective view of a screen portion for printing a land portion and a solder layer in the present example.

FIG. 2 is a plan view of a land portion on which a cream solder layer is printed.

FIG. 3 is an explanatory diagram of printing a solder layer on a screen.

FIG. 4 is a perspective view of a lead terminal of a chip component mounted on a cream solder layer.

FIG. 5 is an explanatory diagram of a molten state of a cream solder layer printed on a land portion.

FIG. 6 is an explanatory diagram of a melted state of a cream solder layer in which printing is misaligned.

FIG. 7 is a side view of the lead terminal in a soldered state.

FIG. 8 is a plan view of another embodiment of a land portion. FIG. 6B is a plan view of another shape of the land portion. FIG. 6C is a plan view of another shape of the land portion. FIG. 6D is a plan view of another shape of the land portion.

FIG. 9 is a perspective view of a conventional land portion and a printing screen.

FIG. 10 is a perspective view of a lead terminal mounted on the solder layer according to the example of FIG. 9;

11 is an explanatory diagram of a melted state of a cream solder layer printed on a land portion according to the example of FIG.

FIG. 12 is an explanatory diagram of a melted state of the cream solder layer in which printing is misaligned according to the example of FIG. 9;

FIG. 13 is an explanatory diagram in which a bridge and insufficient solder are generated due to melting of the cream solder layer in the conventional case.

14A is a side view of an ideal lead terminal soldered state. FIG. FIG. 3B is a side view of the lead terminal being soldered due to insufficient solder.

FIG. 15 is a perspective view of a land portion and a printing screen of a conventional improvement example.

16 is a plan view of a printed state of a cream solder layer on the land portion of FIG.

FIG. 17 is a perspective view showing a state in which lead terminals are mounted on the cream solder layer of FIG.

FIG. 18 is an explanatory diagram of a melted state of the cream solder layer printed on the land portion according to the example of FIG. 15;

FIG. 19 is an explanatory diagram of a melted state of the cream solder layer where printing is misaligned according to the example of FIG. 15;

[Explanation of symbols]

 1 land part 1a island-shaped land part 1b thin land part 2 screen 3 opening 4 cream solder layer 8 lead terminal

Claims (4)

[Claims] 1. In a chip part mounting structure in which lead terminals of chip parts are mounted at high density on a land part of a wiring pattern printed and formed on a wiring board via a solder layer, adjacent land parts are zigzag. And the solder layers are also printed in a zigzag pattern on the lands, and the lead terminals arranged in parallel with the chip components are mounted and soldered on the solder layers. Chip component mounting structure on a wiring board. 2. The chip component mounting structure on a wiring board according to claim 1, wherein the land portion is composed of an island-shaped land portion and a thin land portion in a part thereof, and the land portion and the adjacent island-shaped land portion are thin. A chip component mounting structure on a wiring board, wherein lands and stairs are alternately arranged. 3. The chip component mounting structure on a wiring board according to claim 2, wherein the solder layer is printed and formed in an area of an island-shaped land portion. . 4. The chip component mounting structure on a wiring board according to claim 1, wherein the chip component is an integrated circuit.