Board connector

A plurality of terminal fittings 11 are mounted to a housing 20, board connecting portions 13 having mounting portions 14 at lower ends protrude rearward, fixed fittings 30 having mounting plates 32 at lower edges are mounted to opposite side surfaces of the housing 20, and the mounting portion 14 of each terminal fitting 11 and the mounting plates 32 of the fixed fittings 30 are secured to a PCB 40 by reflow soldering. During the reflow soldering, a drawing force toward the PCB 40 acts on each of the terminal fittings 11 and the fixed fittings 30 based on surface tension of molten solder H, but the center of the fixed fitting 30 in the fore/aft direction of the board connecting portion 13 is positioned forward of the center of gravity position O of a connector 10, and rotation moment Mb toward the PCB 40 acts on the front of the housing 20 based on a drawing force Fb on the side of the fixed fitting 30 to prevent the front from being raised.

TECHNICAL FIELD

The present invention relates to a connector secured to a board by reflow soldering.

BACKGROUND ART

An example of a board connector has been known as disclosed in Japanese Patent Laid-Open No. 5-326049. In securing a housing of the connector mounted with a terminal fitting to a printed circuit board, board securing portions laterally extended are integrally formed at lower ends of opposite sides of the housing, and screws inserted from a back side of the circuit board are screwed into screw holes formed in the board securing portions.

DISCLOSURE OF THE INVENTION

However, it is difficult to secure such a connector to be secured to the circuit board by screwing, and the laterally extended board securing portions increase a space for placing the connector on the circuit board.

SUMMARY OF THE INVENTION

The present invention is completed based on the above described circumstances, and has an object to provide a connector that can be easily secured to a circuit board, and can be placed in a small space.

The present invention has a basic principle that a terminal fitting is connected to a circuit board by reflow soldering, a fixed fitting is mounted to a side surface of a housing, and the fixed fitting is simultaneously secured to the circuit board by reflow soldering. According to this method, the housing can be easily secured to the circuit board, and the space can be reduced.

Further, the present invention solves, in the following manner, a specific problem in simultaneous reflow soldering of the terminal fitting and the fixed fitting to the circuit board as described above.

For reflow soldering of such a connector to a circuit board, solder cream is printed at predetermined positions on the circuit board, and the connector is placed on the circuit board so that soldering portions of a terminal fitting and a fixed fitting come into contact on the solder cream, which is then generally heated to a solder melting temperature. Then, solder particles in the solder cream are molten to be molten solder, which adheres to the soldering portions of the terminal fitting and the fixed fitting in a raised manner by surface tension. Cooling this molten solder allows electrical connection of the terminal fitting and securing of the connector to be simultaneously performed.

However, if the fixed fitting is simply mounted to the housing, and the terminal fitting and the fixed fitting are reflow soldered to the circuit board, the front of the housing may be raised (the side opposite from the terminal fitting protruding) from the circuit board at completion of the soldering, even when it is horizontally placed on the circuit board.

The inventors have studied that the following phenomenon occurs to tilt the connector during reflow soldering of the connector. When the solder cream is molten during reflow soldering, the connector is temporarily raised on the molten solder. On the other hand, the surface tension of the molten solder causes a drawing force for the terminal fitting and the fixed fitting toward the circuit board.

At this time, the fixed fitting is placed on a side wall portion of the housing and near the center of gravity of the connector in the fore/aft direction, and thus a drawing force generated by the fixed fitting is distributed at the front and rear of the center of gravity to counteract most of rotation moment caused by the drawing force. On the other hand, the terminal fitting of the connector is soldered to the circuit board at a position protruding rearward from a rear end surface of the housing, and thus a drawing force acts on a position relatively rearward away from the center of gravity of the connector. Thus, rotation moment caused by the drawing force generated on the terminal fitting significantly acts to tilt the housing so that the rear wall thereof is lowered.

According to one embodiment of the present invention, the fixed fitting is mounted to the side wall portion of the housing so that the center (along the side wall portion) of the board securing portion (which is reflow soldered to the circuit board) is positioned on the side opposite from the rear wall portion of the housing relative to the center of gravity position of the connector. Thus, when the surface tension of the molten solder causes a drawing force to act on the board securing portion of the fixed fitting during reflow soldering of the terminal fitting and the fixed fitting, the force acts as the rotation moment for drawing the front surface of the housing downward, thereby allowing the rotation moment for drawing the rear wall of the housing downward caused by the terminal fitting to be counteracted, and preventing the front surface of the housing from being raised.

DESCRIPTION OF SYMBOLS

BEST MODE FOR CARRYING OUT THE INVENTION

As shown inFIG. 1, a board connector10of the embodiment is configured so that a plurality of terminal fittings11are mounted to a housing20, the housing20is placed on a printed circuit board40(hereinafter simply referred to as a PCB40), each terminal fitting11is connected to the PCB40by reflow soldering, fixed fittings30are mounted to opposite side surfaces of the housing20, and the fixed fittings30are also secured on the PCB40by reflow soldering.

The housing20is made of synthetic resin, and is formed into a generally flat and horizontally oriented rectangular shape with one opened surface as shown inFIGS. 2 and 3. The housing20includes a bottom wall portion20A placed on the PCB40, a rear wall portion20B perpendicularly connected to the bottom wall portion20A, two sidewall portions20C perpendicularly connected to the bottom wall portion20A and positioned on right and left sides of the rear wall portion20B, and a ceiling wall portion20D substantially parallel to the bottom wall portion20A and connected to the rear wall portion20B and the side wall portions20C, and has, at a front surface thereof, a fitting recess21to which a female counterpart housing (not shown) is fitted. At four corners of the bottom wall portion20A, rectangular support protrusions25are formed that slightly protrude and have flat tip surfaces (lower surfaces).

In a rear wall portion22of the housing20that is a back wall of the fitting recess21, a plurality of press fitting holes24are formed in line along the width in two upper and lower rows. Terminal connecting portions12of the terminal fittings11are press fitted into the press fitting holes24from the rear as described below. For example, three press fitting holes24are formed at regular intervals at each end along the width in the upper row, while for example, nine press fitting holes24are formed at regular intervals along the entire width in the lower row, and three holes at each end in the upper row and three holes at each end in the lower row are vertically aligned.

The terminal fittings11include tall first terminal fittings11A and short second terminal fittings11B, and fifteen terminal fittings in total are provided. Each terminal fitting11is basically stamped and formed from copper alloy material by a press, and has, at one end, the terminal connecting portion12connected to a female terminal (not shown) mounted to the counterpart housing, and at the other end, a board connecting portion13connected to a land (not shown) on the PCB40by soldering.

The board connecting portion13is relatively formed into a narrow shape with about half the width of the terminal connecting portion12, and has, at a lower end, a mounting portion14substantially perpendicularly bent rearward. In the first terminal fitting11A, the board connecting portion13is formed from a position offset to the right relative to an axis of the terminal connecting portion12when seen from the rear in a rear end surface of the terminal connecting portion12, while in the second terminal fitting11B, the board connecting portion13is formed from a position offset to the left.

The terminal connecting portion12of the second terminal fitting11B is press fitted from the rear into the press fitting hole24in the lower row, and then the terminal connecting portion12of the first terminal fitting11A is press fitted into the press fitting hole24in the upper row. Thus, as shown inFIG. 3, the terminal connecting portions12of the upper and lower terminal fittings11A and11B protrude with the same length in the fitting recess21of the housing20, and the mounting portions14in the board connecting portions13of the upper and lower terminal fittings11A and11B are horizontally arranged in line at a position protruding rearward of the housing20by a predetermined length.

Fixed fittings30are mounted to the side walls20C on the right and left of the housing20, the fixed fittings30also secure the housing20on the PCB40by soldering.

Each fixed fitting30is formed by pressing a metal plate, the fixed fitting30including a housing securing portion31mounted to the side surface of the housing20, and a board securing portion32integrally perpendicularly bent from a lower edge of the housing securing portion31and positioned on the PCB40as shown inFIG. 4.

The housing securing portion31has three steps with decreasing widths from the upper portion toward the lower portion, and has engaging protrusions33at opposite edges in the middle step. The opposite side walls20C of the housing20each have a mounting groove27into which the housing securing portion31of the fixed fitting30can be inserted from above.

The fixed fitting30is inserted, at the housing securing portion31, into the mounting groove27from above, pushed into the mounting groove27while the engaging protrusions33engage side edges of the mounting groove27, stopped at a predetermined position, and retained and mounted so that a lower surface of the board securing portion32slightly protrudes downward from a lower surface of the bottom wall portion20A of the housing20to be flush with a lower surface of the support protrusion25, though not shown in detail.

The board securing portion32of the fixed fitting30is retained at a depth slightly protruding from the side wall portion20C of the housing20when inserted into the mounting groove27. The board securing portion32is shown with four solder entering holes35formed at regular intervals along the length, and slits36perpendicular to the length of the board securing portion32are formed between the solder entering holes35and the middle slit36is formed to be raised from the board securing portion32to a lower end of the housing securing portion31.

The fore/aft mounting position of the fixed fitting30having the above described configuration is determined so that the center of the board securing portion32along the side wall portion20C is positioned forward of the center of gravity position (denoted by reference character O inFIG. 6) of the connector10(that is, the side opposite from the rear wall portion20B of the housing20).

More specifically, in the embodiment, when a distance La from the center of gravity position O to a root of the mounting portion14of the terminal fitting11is 3.0 mm, a distance Lb from the center of gravity position O to the center of the fixed fitting30is set to 5.0 mm.

The above described connector10is mounted on the PCB40by reflow soldering by the following procedure:

Portions to be soldered on the surface of the PCB40are provided with copper foil (not shown), and solder cream for reflow soldering is previously adhered to the foil. Then, the connector10is placed at a predetermined position on the surface of the PCB40, thus the mounting portion14of each terminal fitting11is placed over the solder cream, and the board securing portions32of the fixed fittings30are also placed over the solder cream.

When the PCB40on which the connector10is placed is moved into a high temperature furnace (not shown) in this state, solder in the solder cream previously coated on the PCB40is molten to form a molten solder layer, which adheres to the mounting portion14of each terminal fitting11and the board securing portions32of the fixed fittings30. When the PCB40is moved out of the high temperature furnace to cool the molten solder, the mounting portion14of each terminal fitting11is secured on the copper foil on the PCB40and conductively connected. The board securing portions32of the fixed fittings30are also secured to separate copper foil on the PCB40, that is, the housing20is mounted to the PCB40.

For the adhering state of the solder, the solder H adheres along a peripheral edge of each mounting portion14in a raised manner on the side of the terminal fitting11as shown inFIG. 7, and a component of force of the surface tension that acts at this time causes a drawing force for the mounting portion14toward the PCB40. The drawing force for one mounting portion14is, for example, about 0.8 (N/m), and thus a drawing force Fa for fifteen terminal fittings11is Fa=0.8 (N/m)*15=12 (N/m).

On the other hand, on the side of the fixed fitting30, as shown inFIG. 8, the solder H adheres to the peripheral edge of the divided board securing portion32and the peripheral edge of the solder entering hole35in a raised manner, and a component of force of the surface tension that acts at this time similarly causes a drawing force for the board securing portion32toward the PCB40. The drawing force for one board securing portion32is, for example, about 8.0 (N/m), and thus a drawing force Fb for two right and left fixed fittings30is Fb=8.0 (N/m)*2=16 (N/m).

Further, based on the drawing forces, rotation moment Ma of the terminal fitting11toward the PCB40at the rear of the housing20, and rotation moment Mb of the front of the housing20toward the PCB40act, for example, with the center of gravity position O of the connector10at the center.

Specifically, the rotation moment Ma at the rear is Ma=Fa*La=12 (N/m)*3.0 (mm)=36.0 (N), and

the rotation moment Mb at the front is Mb=Fb*Lb=16 (N/m)*5.0 (mm)=80.0 (N).

Thus, the rotation moment Ma at the rear is smaller than the rotation moment Mb at the front. In brief, a rotation force for pressing the front of the housing20against the PCB40with the center of gravity position O at the center more significantly acts on the housing20, and thus the housing20is reliably secured on the PCB40without the front being raised.

The possible factors for increasing the rotation moment Mb at the front may be as follows:

First, the surface tension of the solder increases with increasing length of the portion at the peripheral edge to which the solder adheres in a raised manner. Thus, the board securing portion32of the fixed fitting30has the slits36and is divided, and has the solder entering holes35. The solder adheres to the peripheral edge of the divided board securing portion32and the peripheral edge of the solder entering hole35in the raised manner, that is, the length of the peripheral edge to which the solder adheres in the raised manner is long, thereby increasing the surface tension. This allows the rotation moment Mb at the front to be increased.

The mounting position of the fixed fitting30is forward away from the center of gravity position O. This increases the length of a so-called arm for obtaining the rotation moment Mb at the front, thereby increasing the rotation moment Mb.

In the embodiment, the support protrusions25are provided at the four corners of the bottom wall portion20A of the housing20, and thus the contact positions of the housing20with the PCB40are determined at the four corners. Thus, the tilt of the housing20can be more reliably prevented in this embodiment. Without the support protrusions25, the center (and therearound) of the bottom wall portion20A of the housing20locally comes into contact with the surface of the PCB40depending on forming accuracy of the housing20or flatness of the surface of the PCB40to allow or facilitate the tilt of the housing20.

In a connector of the type such that a terminal fitting is previously inserted and mounted into a cavity formed in a housing, there is a slight gap between an inner wall of the cavity and the terminal fitting for allowing insertion of the terminal fitting, and thus if surface tension when molten solder adheres to aboard connecting portion of the terminal fitting causes a drawing force to act on the terminal fitting, the terminal fitting is slightly moved and the drawing force does not act on the housing. On the other hand, if the terminal fitting11is not press fitted into the housing20as in this embodiment, the above described movement of the terminal fitting11is not allowed at all, and thus the drawing force that acts on the terminal fitting11immediately acts as the drawing force for the housing20. However, as described above, the rotation moment for pressing the front of the housing20against the PCB40significantly acts in the embodiment, and thus the housing20is reliably secured on the PCB40without the front being raised.

The present invention is not limited to the embodiment described above with reference to the drawings, and the technical scope of the present invention covers, for example, the following embodiments.

(1) Numerical values of the surface tension or numerical values of the distance from the center of gravity position described in the embodiment are merely examples, and may be replaced by other numerical values.

(2) In the above described embodiment, the board securing portion32of the fixed fitting30has both the slit36and the hole35, but the board securing portion32may have either or none of slit36and the hole35.