JP2917537B2 - Mounting method of IC package for surface mounting - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for mounting a surface mount IC package on a printed wiring board.

[0002]

2. Description of the Related Art Today, as electronic devices are being miniaturized, in order to increase the component mounting density on a printed wiring board, examples of using surface-mounted circuit components having no lead wires as circuit components. Are increasing. These surface mount circuit components include chip-type components having electrodes at both ends of a main body such as a resistor and a capacitor, and various IC packages having lead terminals on two or four sides.

[0003] As a method of mounting these surface mounting components on a printed wiring board, there are mainly a flow method of fixing a component with an adhesive and then soldering a land of the printed wiring board and an electrode of the component by flow soldering. There is a reflow method in which a cream solder is applied to a land portion of a printed wiring board, components are mounted, the cream solder is melted, cooled and fixed, and a land of the printed wiring board and an electrode of the component are soldered. In the surface mounting IC package, a mounting method mainly using cream solder reflow is often used.

That is, after applying cream solder to a land portion of a printed wiring board corresponding to a lead terminal of an IC package for surface mounting using a screen plate or a dispenser, the IC package is mounted, and infrared rays, hot air, or In this method, the cream solder is melted, cooled, and fixed by other heating equipment, and the lead terminals of the IC package and the lands of the printed wiring board are soldered.

In this case, generally, a cream solder printing mask having an independent opening is prepared in correspondence with each land of the printed wiring board, and the cream solder is printed on each land using the mask. Apply, but I
When the pitch of the lead terminals of the C package becomes narrower and the width of the corresponding land becomes narrower, the independent opening of the cream solder printing mask also becomes smaller, and the cream solder is not sufficiently transferred from the opening during printing. It becomes difficult to secure the required thickness of the cream solder, that is, the amount. Furthermore, it is extremely difficult to form an independent opening in a mask having a mask thickness that secures the amount of cream solder on a land of a printed wiring board corresponding to an IC package having a lead terminal pitch of 0.5 mm. .

For this reason, conventionally, as shown in FIG. 2A, a specific part including lands 1a, 1b, 1c, 1d, 1e of a printed wiring board corresponding to lead terminals on each side of an IC package and land gaps. A mask 7 for cream solder printing that can be printed and applied to all parts of the area is produced,
Using this, the cream solder 4 is applied, and after the IC package is mounted, the solder 6 is agglomerated on the lands during reflow, so that the lead terminals 5 of the IC package and the lands 1a, 1b, 1c, 1d, 1e of the printed wiring board are formed. Is used.

[0007]

However, although the land shape of the printed wiring board corresponding to the lead terminal of the IC package is the same, as shown in FIG. 3, the land for the surface mounting IC package of the printed wiring board is used. 1a, 1
Various conductive patterns 2 having different lengths, widths, and shapes are connected to b, 1c, 1d, and 1e, and a solder resist 3 is formed. Different for each pattern, the heating state in each land is not uniform during reflow. Therefore, in a method of applying the cream solder 4 as shown in FIG. 2B, mounting the leads 5 of the surface mounting IC package, and reflowing, as shown in FIG. , The fixed lands 1a, 1b, 1c,
The thickness of the solder 6 on 1d and 1e varies greatly from land to land, and the bonding strength varies, reducing the reliability of solder bonding. There has been a problem that the solder ball deteriorates the insulation property, or peels off due to vibration during transportation or operation of the electronic device, which affects the operation of the electronic device.

SUMMARY OF THE INVENTION The present invention solves the above-mentioned conventional problems.
An object of the present invention is to provide a mounting method for making the solder thickness of a land for a C package uniform.

[0009]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention relates to a method of manufacturing a printed circuit board, which corresponds to a lead terminal on each side of a surface mounting IC package. After applying the cream solder to the part, and after mounting the IC package, melting and fixing the cream solder, and using the mounting method of connecting the lead terminals of the IC package and the lands of the printed wiring board, connect to each land. This is a mounting method in which cream solder is applied while partially changing the area according to the length, width and shape of the conductor pattern.

[0010]

According to this method, the heat conductivity per conductor pattern including the land differs for each pattern due to the difference in length, width and shape of the conductor pattern to which the land of the printed wiring board is connected. Even when the heating condition in each land is not uniform, the area of the cream solder applied on the land changes according to the heat conductivity of one conductor pattern. The time required for melting the cream solder is short, and if the adjacent lands have poor heat conductivity, the melting lands are started first, and the independent lands agglomerate the cream solder that should be agglomerated in the adjacent lands. Since many cream solders are applied to the lands having poor heat conductivity, the thickness of the solder on each land after cooling and solidification can be made uniform.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is an explanatory view of an embodiment of the present invention. FIG. 1 (a) shows an IC for surface mounting of a printed wiring board.
FIG. 1B is a plan view of a state immediately before the printing of the cream solder in which the package land and the cream solder printing mask are superimposed, and FIG. 1B is a cross-section of the land where the cream solder is applied and the surface mounting IC package is mounted. Figure, Figure 1
(C) is a sectional view of a land portion after reflow.

In FIG. 1, the same parts as those in FIG. 2 are denoted by the same reference numerals, and description thereof will be omitted. Reference numeral 8 denotes a cream solder printing mask that enables the mounting method of the present invention, and reference numeral 8a denotes a cutout portion of the cream solder printing mask.

FIGS. 1 (a), 1 (b), and 1 (b) show a method of mounting the surface mounting IC package configured as described above.
This will be described with reference to FIG. First, a conductor pattern 2 and lands 1a, 1b, 1 are formed on an insulating substrate by a conventional manufacturing method.
The printed wiring board is obtained by forming c, 1d, 1e and the solder resist 3. Next, the lands 1a, 1b, 1c, 1d,
In a specific region including the land 1e and the land gap, a cutout 8a is formed in a portion excluding a portion corresponding to the land 1a connected to the wide circuit and the land 1e connected to the conductor pattern 2 having a long length. The cream solder printing mask 8 whose area is partially changed by using the provided artwork film is manufactured. Land pitch 0.5m
For a surface mounting land having a land width of 0.25 mm and a land gap of 0.25 mm, the area of the mask 8 for cream solder printing is 0.2 mm larger on one side than the outer periphery of the land row. Notch 8a is 0.15mm on one side
The cream solder printing mask 8 has a notched shape. After printing and applying the cream solder 4 using the cream solder printing mask 8, the surface mounting IC
The lead terminals 5 of the package are connected to the lands 1a, 1b, 1c,
After alignment with 1d and 1e, it is mounted, and the cream solder 4 is melted by a method such as an infrared reflow method and cooled.
After solidification, the lead terminals 5 of the surface mounting IC package and the lands 1a, 1b, 1c, 1d, 1e of the printed wiring board are soldered to complete the mounting of the IC package. As shown in FIG. 1 (c), the difference in thickness between the land with the smallest solder thickness and the land with the largest solder thickness from the land surface in the conventional method was about 80 μm, but in the method of the present invention, Bonding with the solder 10 having a more uniform thickness of 30 to 40 μm was realized.

[0014]

As described above, the present invention relates to a surface mount IC.
It is possible to provide uniform solder thickness at the joints between the package lead terminals and the printed wiring board, suppress variations in joint strength, and realize an excellent mounting method that can improve solder joint reliability. You can do it.

[Brief description of the drawings]

FIG. 1 (a) is a plan view showing a state immediately before cream solder printing in which a land portion for a surface mounting IC package of a printed wiring board and a cream solder printing mask are overlapped in an embodiment of the present invention. Sectional view of the land portion where the cream solder is applied in the embodiment and the IC package for surface mounting is mounted. (C) is a cross-sectional view of the land portion after reflow in the embodiment.

FIG. 2 (a) shows a conventional printed wiring board surface mount I.
The plan view of the state immediately before the cream solder printing in which the land portion for the C package and the mask for the cream solder printing are superimposed on each other is shown in FIG.
Sectional view of land part with C package mounted (c) Sectional view of land part after conventional reflow

FIG. 3 is a plan view of a land portion for an IC package for surface mounting of a printed wiring board.

[Explanation of symbols]

1a Land for IC package for surface mounting of printed wiring board 1b Land for IC package for surface mounting of printed wiring board 1c Land for IC package for surface mounting of printed wiring board 1d Land for IC package for surface mounting of printed wiring board 1e Printing Land for IC package for surface mounting of wiring board 2 Conductor pattern 3 Solder resist 4 Cream solder 5 Lead terminal of IC package for surface mounting 6 Solder after cooling and solidification 8 Mask for cream solder printing 8a Notch

Claims (1)

(57) [Claims] An independent, non-connected conductor pattern
Lands and conductor patterns with different lengths, widths and shapes.
A printed wiring board having individual lands connected thereto, including individual lands and land gaps of the printed wiring board.
All parts of a specific area through a printing mask.
After applying the solder paste and mounting the IC package,
Melts the solder for the
Surface to connect lead terminals and printed circuit board lands
In the mounting method of the mounting IC package, the length of the independent land and the length of the connected conductor pattern,
Difference in thermal conductivity between individual lands due to differences in width and shape
Clear through a printing mask with a corresponding notch
IC for surface mounting, characterized by applying a solder paste
Package implementation method.