CN108668439B - Spring plate fixing structure and mounting method - Google Patents

Abstract

The invention discloses a spring plate fixing structure which is different from the traditional fixing structure in that at least two first through holes are formed in a spring plate, positioning columns are arranged in the first through holes, the positioning columns penetrate through bonding pads downwards and extend into a printed circuit board, and a flat plate is arranged at the upper end of each positioning column. The second through hole arranged on the printed circuit board and used for accommodating the positioning column is in a conical hole shape with a large upper end diameter and a small lower end diameter. The method for installing the fixing structure is also disclosed. The fixing structure not only effectively solves the problem of weak welding strength of the elastic sheet, reduces the defective rate of the missing elastic sheet, reduces the maintenance cost, the labor cost and the rejection rate of the assembled printed circuit board, saves the material cost, but also is simple to operate, and only needs to add one step compared with the traditional fixing structure, so that the processing efficiency is not reduced.

Description

Spring plate fixing structure and mounting method

Technical Field

The invention relates to the technical field of electronic products, in particular to a fixing structure of an elastic sheet in an electronic product and an installation method of the fixing structure.

Background

At present, a part of an elastic sheet is used in a very large number of electronic products, and in the assembling process, the part of the elastic sheet is needed to connect the upper part and the lower part, so that the electronic products can play a good role in conducting.

However, the spring sheet on many products is very easy to be lost, and the loss is not the loss of the machine placement, but the spring sheet is bumped by people or some careless operation after the machine placement is finished, so that the loss of the spring sheet is caused. Moreover, when serious, the bonding PADs (PAD) of the welding shrapnel are fallen off, so that the Printed Circuit Board (PCBA) is scrapped, and the cost loss is quite high. The adverse events such as the spring being knocked off are very numerous, and even if the manual operation is required to be careful, the adverse events cannot be completely avoided.

The real reason for this problem is that the spring plate itself is relatively small, so that the area that can be welded is relatively small, and the welding strength of the spring plate is relatively weak.

According to statistics, the reject ratio of missing spring pieces is up to 7%, and the reject ratio of the assembled printed circuit board can reach 3% due to the falling of bonding pads in 7%, so that the loss is relatively large.

Disclosure of Invention

In view of the above problems, the invention provides a spring fixing structure and an installation method thereof, wherein the fixing structure is convenient to install, effectively improves the fixing strength of the spring and reduces the defective rate of spring missing.

The technical scheme adopted for solving the technical problems is as follows:

the elastic sheet fixing structure comprises an elastic sheet, wherein at least two first through holes are formed in the elastic sheet, positioning columns are arranged in the first through holes, the positioning columns penetrate through bonding pads downwards and extend into a printed circuit board, and a flat plate is arranged at the upper end of each positioning column;

the second through hole arranged on the printed circuit board and used for accommodating the positioning column is in a conical hole shape with a large upper end diameter and a small lower end diameter.

Further, a groove is formed in the cylindrical surface of the positioning column, and solder paste is filled in the groove.

Further, the grooves are axially arranged, and a plurality of the grooves are uniformly distributed along the circumferential direction.

Further, the grooves are spiral.

Further, an elastic pressing sheet inclined inwards to the lower side is arranged at the edge of the flat plate, and a plurality of elastic pressing sheets are uniformly distributed along the circumferential direction.

Further, a diameter of a third through hole provided on the bonding pad for accommodating the positioning column is larger than a diameter of the positioning column.

Further, the diameter of the first through hole is equal to the diameter of the positioning column.

Further, the taper of the second through hole is 3 degrees to 5 degrees.

The method for installing the elastic sheet fixing structure comprises the following steps,

firstly, smearing solder paste on a bonding pad, and then placing an elastic sheet above the solder paste;

secondly, smearing solder paste in the grooves of the positioning columns to enable the grooves to be filled with the solder paste;

thirdly, inserting the positioning column into the printed circuit board until the elastic pressing sheet on the positioning column is in a compressed state;

fourthly, placing the steel wire into a reflow oven for heating welding.

The beneficial effects of the invention are as follows:

1. the fixing structure effectively solves the problem of weak welding strength of the elastic sheet, reduces the defective rate of the missing elastic sheet, reduces the maintenance cost, the labor cost and the rejection rate of the assembled printed circuit board, and saves the material cost.

2. Because the size of the positioning column is smaller, the positioning column is easy to fall off in the process of being carried to the reflow oven, and the first through hole on the printed circuit board is designed into a conical hole with a large upper end diameter and a small lower end diameter, so that tension force is generated between the positioning column and the first through hole during installation, and falling off in the process of being carried and moved is avoided.

3. The groove is formed in the positioning column, and the solder paste is filled in the groove, so that the welding strength between the positioning column and the bonding pad is increased, and the welding strength of the elastic sheet is further improved.

4. Through setting up the flat board on the top of reference column, set up the elasticity preforming in dull and stereotyped edge to make the diameter of the second through-hole on the pad greater than the diameter of reference column, like this, on the one hand in the back welding stove internal heating, after the solder paste melts, can be under the pressure of elasticity preforming, impress the solder paste after partly melting between reference column and second through-hole, and reference column and the first through-hole, increase welded fastness. On the other hand, because the molten solder paste has fluidity, the solder paste is not present on the part of the welding surface of the elastic sheet, and the lower side surface of the elastic sheet can be always contacted with the solder paste by arranging the elastic pressing sheet, so that 'empty drum' is avoided.

Drawings

FIG. 1 is a schematic structural view of the present fixing structure;

FIG. 2 is an enlarged schematic view of the portion A in FIG. 1;

FIG. 3 is a top view of the present mounting structure;

FIG. 4 is a schematic perspective view of a positioning post;

FIG. 5 is an enlarged schematic view of the portion B of FIG. 4;

FIG. 6 is a schematic perspective view of a positioning post in a second embodiment;

fig. 7 is an enlarged schematic view of the portion C in fig. 6.

In the figure: the printed circuit board comprises a 1-printed circuit board, a 11-second through hole, a 2-bonding pad, a 21-third through hole, 3-solder paste, a 4-shrapnel, a 5-positioning column, a 51-flat plate, a 511-elastic pressing sheet and a 52-groove.

Detailed Description

Example 1

As shown in fig. 1, a fixing structure of an elastic sheet 4 includes a first through hole disposed on the elastic sheet 4, a positioning column 5 is disposed in the first through hole, and the positioning column 5 extends into the printed circuit board 1 by penetrating the bonding pad 2 downwards. The printed circuit board 1 is provided with a second through hole 11 for accommodating the positioning column 5, and the bonding pad 2 is provided with a third through hole 21 for accommodating the positioning column 5. The upper end of the positioning column 5 is provided with a circular flat plate 51.

Since the assembly printed circuit board 1 with the spring plate 4 mounted thereon needs to be placed in the reflow oven during the soldering process of the spring plate 4, the fan in the reflow oven can cause the circulation of air current in the reflow oven. At this time, the solder paste 3 between the spring plate 4 and the bonding pad 2 is not melted and welded firmly, so that the spring plate 4 may rotate around the positioning shaft under the action of the air flow.

In order to avoid this, as shown in fig. 3, at least two positioning posts 5 are disposed on the spring plate 4. As a specific embodiment, three positioning posts 5 are disposed on the elastic sheet 4 in this embodiment, and the three positioning posts 5 are arranged in a triangle shape.

When the spring plate 4 is welded, the positioning column 5 is inserted into the printed circuit board 1, and then the printed circuit board 1 is conveyed into a reflow oven for heating and welding. Because the volume of the spring plate 4 is smaller, the corresponding positioning column 5 is also smaller, and the spring plate is easy to fall off due to shaking in the carrying process.

For this purpose, as shown in fig. 1 and 2, the second through hole 11 is a tapered hole with a larger diameter at the upper end and a smaller diameter at the lower end. Therefore, when the positioning column 5 is inserted into the printed circuit board 1, tension force can be generated between the positioning column 5 and the printed circuit board 1, and the positioning column 5 is prevented from falling off in the carrying process. The second through hole 11 is designed as a tapered hole here because of the thicker thickness of the printed circuit board 1 relative to the pad 2, which is easy to process.

Preferably, the taper angle α of the second through hole 11 is 3 ° -5 °.

In order to increase the welding strength between the positioning column 5 and the bonding pad 2, as shown in fig. 4 and 5, the cylindrical surface of the positioning column 5 is provided with grooves 52 extending along the axial direction, a plurality of the grooves 52 are uniformly distributed along the circumferential direction, and the grooves 52 are filled with solder paste 3. As a specific embodiment, the number of the grooves 52 in this embodiment is four.

Since the melted solder paste 3 after heating has fluidity, the thickness of the solder paste 3 is reduced compared with that before heating, and if the elastic sheet 4 is tightly attached to the upper surface of the solder paste 3 by the gravity of the elastic sheet 4, the adhesion of the elastic sheet 4 to the upper surface of the solder paste 3 is difficult, particularly, under the influence of the air flow in the reflow oven, the adhesion of the solder paste is more difficult, and "hollowing" is easy to occur.

For this, as shown in fig. 1 and 4, an elastic pressing piece 511 inclined toward the inner lower side is provided at the edge of the flat plate 51, and a plurality of the elastic pressing pieces 511 are uniformly distributed in the circumferential direction. As a specific embodiment, the number of the elastic pressing pieces 511 in this embodiment is three.

When installing reference column 5 like this, make elasticity preforming 511 be in compressed state through the downforce, after solder paste 3 is heated and melts in the reflow oven, under the restoring force effect of elasticity preforming 511, the bullet screen can the downward movement, guarantees that the downside of shell fragment 4 pastes closely solder paste 3 all the time, avoids "empty drum" to take place, guarantees welded intensity.

As shown in fig. 2, the diameter N of the third through hole 21 is larger than the diameter of the positioning post 5, and preferably the diameter of the larger end of the second through hole 11 is equal to the diameter N of the third through hole 21.

Thus, as shown in fig. 2, in the reflow furnace, the melted solder paste 3 flows between the positioning post 5 and the third through hole 21 and between the positioning post 5 and the second through hole 11 under the force of the elastic pressing piece 511, and the strength of the soldering is increased.

In order to avoid that a part of melted solder paste 3 overflows from the first through hole under the action of the elastic pressing piece 511, the diameter M of the first through hole is equal to the diameter of the positioning column 5.

Example two

As shown in fig. 6 and 7, the groove 52 is spiral, and the other structures are the same as those of the first embodiment.

The method for installing the elastic sheet 4 fixing structure comprises the following steps:

first, solder paste 3 is applied on the bonding pad 2, and then the spring plate 4 is placed above the solder paste 3.

Secondly, the solder paste 3 is smeared in the groove 52 of the positioning column 5, so that the groove 52 is filled with the solder paste 3.

Thirdly, the positioning column 5 is inserted into the printed circuit board 1 through the elastic sheet 4 and the bonding pad 2 in sequence until the elastic pressing sheet 511 on the positioning column 5 is in a compressed state.

Fourth, the printed circuit board 1 with the spring plate 4 is placed in a reflow oven and soldered by heating.

The heat welding performed by the reflow oven belongs to the prior art, and the temperature setting and other process parameters and steps of the heat welding also belong to the prior art, and are not described herein.

Claims (5)

1. The utility model provides a shell fragment fixed knot constructs which characterized in that: the elastic sheet is provided with at least two first through holes, a positioning column is arranged in the first through holes, the positioning column penetrates through the bonding pad downwards to extend into the printed circuit board, and the upper end of the positioning column is provided with a flat plate;

the second through hole arranged on the printed circuit board and used for accommodating the positioning column is in a conical hole shape with a large upper end diameter and a small lower end diameter;

a groove is formed in the cylindrical surface of the positioning column, and solder paste is filled in the groove;

the grooves are axially arranged, and a plurality of the grooves are uniformly distributed along the circumferential direction or the grooves are spiral;

the edge of the flat plate is provided with an elastic pressing sheet which inclines inwards and downwards, and a plurality of elastic pressing sheets are uniformly distributed along the circumferential direction.

2. A spring plate fixing structure according to claim 1, wherein: the diameter of the third through hole which is arranged on the bonding pad and used for accommodating the positioning column is larger than that of the positioning column.

3. A spring plate fixing structure according to claim 1, wherein: the diameter of the first through hole is equal to the diameter of the positioning column.

4. A spring plate fixing structure according to claim 1, wherein: the taper of the second through hole is 3-5 degrees.

5. A method of installing a clip securing structure according to any one of claims 1 to 4, wherein: comprises the steps of,

firstly, smearing solder paste on a bonding pad, and then placing an elastic sheet above the solder paste;

secondly, smearing solder paste in the grooves of the positioning columns to enable the grooves to be filled with the solder paste;

thirdly, the positioning column sequentially penetrates through the elastic sheet and the bonding pad to be inserted into the printed circuit board until the elastic pressing sheet on the positioning column is in a compressed state;

fourthly, placing the steel wire into a reflow oven for heating welding.