CN100499967C - Printed steel plate applied to surface adhesion assembly of electronic part without extension pin and manufacturing process - Google Patents

Abstract

A printed steel plate for surface-mounted electronic parts and its surface-mounted manufacturing process is used to coat a conductive adhesive layer on the bonding pad on the surface of the printed circuit board. The welding pad is corresponding to the contact electrode of the surface-mounted electronic component. The printing steel plate is provided with a plurality of hollowed-out trapezoidal openings which just correspond to the welding pads, so that the conductive adhesive layer is coated on the welding pads through the trapezoidal openings. Since the conductive adhesive layer coated on the bonding pad has a trapezoidal appearance, even if the conductive adhesive layer is pressed by the contact electrode, the conductive adhesive layer extends slightly towards two sides, so that the defects of bridging short circuit or empty welding and the like in the subsequent reflow process are avoided.

Description

Printed steel plate and manufacturing process applied to the surface mount assembly of electronic parts without extension feet

(1) Technical field

The present invention relates to a surface mount manufacturing process (Surface Mounted Technology; SMT) of electronic components, in particular to a printed steel plate and related manufacturing process applied to the surface mount assembly of surface mounted electronic components.

(2) Background technology

With the progress of integrated circuit production technology, the design and production of electronic components continue to develop towards the trend of miniaturization, and because they have larger-scale and highly integrated electronic circuits, their product functions are also more complete. In this case, the traditional Through Hole Technology (THT) will take up a lot of space on the printed circuit board because the size cannot be further reduced. In addition, the "plug-in" assembly method requires drilling a hole for each pin, so the pins of this type of component will actually occupy the space on both sides of the printed circuit board, and the solder joints at the connection are relatively large. In this way, in today's electronic component packaging procedures, a large number of surface mount technology (Surface Mounted Technology; SMT) is used to assemble electronic components on the printed circuit board.

Parts using surface mount packages do not need to drill holes in the PCB to provide insertion of each pin because the pins are soldered to the PCB on the same side as the part. In other words, after using the surface mount technology, electronic components can be soldered on both sides of the printed circuit board at the same time, thereby greatly improving the space utilization rate of the circuit board. In addition, due to the smaller volume of surface-mounted parts (SMT), compared with traditional through-hole parts (THT), parts on printed circuit boards using SMT technology are much denser. In addition, the cost of SMT packaging parts is also relatively cheap, so it has jumped into the mainstream of today's printed circuit board assembly manufacturing process. However, as the volume of electronic components continues to shrink, considerable difficulties are encountered in SMT technology.

Take the most basic and necessary component in electronic products—resistor as an example. Because it is widely used in the adjustment of voltage and current in electronic circuits, all electronic and electrical products such as computers, computers and peripheral equipment, televisions, mobile phones and Instruments, etc. need to use a large number of resistors. In particular, due to the demand for resistors in recent years, which tends to be small in size, high in power, high in quality stability and high in technical complexity, it is applied to the chip exclusion of surface mount technology, because of the high precision and complexity of the product, It is widely used in high value-added industries such as computers, communications, space, military, and high technology, and has become the mainstream of market development.

However, with the size specification of the new generation of thick film resistors, when the size specification of 0603 (1.6 x 0.8 x 0.45mm) is reduced to the size specification of 0402 (1×0.5×0.35mm), due to the volume ratio of 0402 row group compared with 0603 package row The group size is more than 50% smaller. Therefore, when using SMT technology to assemble on a printed circuit board, the adjacent pads are often densely arranged and small in size, resulting in voids in the printed and coated conductive adhesive after the reflow process. Defects such as welding or short circuit.

Please refer to Figure 1, which shows a typical 0402 size array structure 10. As shown in the figure, the array structure 10 includes an alumina ceramic substrate 12 and a thick film resistance layer 14 formed on the surface of the alumina ceramic substrate 12 . A protection layer 16 is coated on the surface of the thick film resistor layer 14 and the alumina ceramic substrate 12 . It should be noted that several electrodes 18 are formed on two sides of the bottom surface of the array structure 10 to connect to the thick film resistor layer 14 . The electrodes 18 can be divided into terminal electrodes 18 a located at the four corners and line electrodes 18 b located along the side edge of the substrate 12 according to the positions distributed on the sides of the alumina ceramic substrate 12 . As shown in the figure, the terminal electrodes 18a have an "L" shape and are slightly larger than the rectangular line electrodes 18b. In this way, when performing surface mount technology, the purpose of assembling fixed parts can be achieved by soldering these electrodes 18 to the pads on the printed circuit board.

During the surface mount process, the conductive adhesive is coated on the pads of the printed circuit board by stencil printing. Please refer to FIG. 2 , taking the above-mentioned 0402 chip array as an example, there are eight rectangular pads 20 fabricated on the printed circuit board, arranged in two rows and corresponding to the electrodes 18 on the array structure 10 . When coating the conductive adhesive, a steel plate 22 is covered on the printed circuit board. There are eight rectangular openings 24 on the steel plate 22, which just expose the above-mentioned rectangular welding pads 20 respectively, so that the conductive adhesive can be coated on the surface of the rectangular welding pads 20 through these rectangular openings 24 during the coating process. . In this way, after the steel plate 22 is removed, a rectangular conductive adhesive layer remains on each rectangular pad 20 . Then, the 0402 array structure 10 can be pressed onto these solder pads 20 , and assembled and fixed through the subsequent reflow process, so that the electrodes 18 of the array structure 10 and the solder pads 20 are electrically connected.

However, it is worth noting that after the array specification changed from the original 0603 size to the 0402 size, the distance between adjacent conductive adhesives was reduced to about 8 mils (mil), and the arrangement of the array structure At 10 o'clock, being pressed by the electrodes 18, the rectangular conductive adhesive layer tends to spread to both sides, so it is easy to cause soldering errors in the subsequent reflow process. Especially when the conductive adhesive layer is heated and melted, the adjacent conductive adhesive may flow and bridge to cause a short circuit effect, or be pulled by the surface tension of the solder ball, resulting in a situation where some electrodes are empty soldered.

In this way, in addition to reducing the assembly yield of related parts, more labor costs are required for repair and inspection work. Moreover, in order to further reduce the size of various electronic components and improve the integration and related performance of printed circuit boards, the new chip array has been reduced from 0402 size to 0201 size specification. It is foreseeable that under the 0201 size specification, the distance between the rectangular conductive adhesives will be further reduced, and the above-mentioned short circuit or empty soldering problems will become more serious.

(3) Contents of the invention

In view of the above problems, the purpose of the present invention is to provide a printed steel plate and manufacturing process for adhesive assembly applied to the surface of an electronic component, which can prevent problems such as bridging short circuits or empty soldering defects.

To achieve the above purpose, the present invention provides a design of a printed steel plate for surface-mounted electronic components. The printed steel plate is used to coat the conductive adhesive layer on the soldering pads on the surface of the printed circuit board, and these soldering pads correspond to the contact electrodes of the surface-mounted electronic components. The printed steel plate has a plurality of trapezoidal openings, just corresponding to these welding pads, so that a trapezoidal conductive adhesive layer can be coated on the welding pads through the trapezoidal openings.

In one embodiment, the several openings on the surface-mounted electronic parts of the printed steel sheet can be arranged in two rows parallel to each other, and according to the positions of the openings in each row, they can be divided into the first trapezoidal opening and the first trapezoidal opening. Second trapezoidal opening. The first trapezoidal openings are located at both ends of each row of openings. Each first trapezoidal opening has a first short side and a first long side parallel to each other, the first long side is closer to the other row of openings, and the first short side is farther away from the other row of openings. The second trapezoidal opening is located between the left and right first trapezoidal openings, and each second trapezoidal opening also has a second short side and a second long side parallel to each other, the second short side is closer to the other row of openings, and the second long side The edge is further away from the other row of openings.

By covering the above-mentioned printed steel plate on the printed circuit board, a conductive adhesive layer can be coated on the surface of each pad. Wherein, the first conductive adhesive layer coated by the first trapezoidal opening also has a first short side and a first long side parallel to each other. The first long side is located outside the pad, and the first short side is located inside the pad. As for, the second conductive adhesive layer coated through the second trapezoidal opening also has a second short side and a second long side parallel to each other. Its second short side is located inside the pad, and its second long side is located outside the pad.

After removing the printed steel plate, the surface mount electronic components can be placed on the printed circuit board, and each of the electrodes touches the corresponding conductive adhesive layer. Then, a reflow process is performed to fix the surface mount electronic components on the printed circuit board.

According to the present invention, by changing the shape of the opening on the printed steel plate to a trapezoid, the coating amount of the conductive adhesive on the inner side of the opening can be reduced, so as to avoid the above-mentioned defects in the subsequent reflow process.

(4) Description of drawings

Through the following detailed description combined with the accompanying drawings, the above content and many advantages of this invention can be easily understood, wherein:

Figure 1 shows the structural diagram of the 0402 exclusion element;

Figure 2 shows the opening design of the printed steel plate applied to the surface mount electronic parts in the traditional technology;

Fig. 3 shows the opening design of the printed steel plate applied to the surface mount electronic parts in an embodiment of the present invention; and

FIG. 4 shows a conductive adhesive layer coated on a printed circuit board using a printed steel plate according to an embodiment of the present invention.

(5) specific implementation

Please refer to FIG. 3 , which shows a printed steel plate 30 provided by an embodiment of the present invention. As mentioned above, this printed steel plate 30 is an adhesive manufacturing process applied to the surface of an electronic component (such as a surface mount device, surfacemounting device; SMD), so that several electrodes of the surface mounted electronic component and several electrodes on the printed circuit board Pads are bonded together. A plurality of openings 32 are made on the printed steel plate 30. When the printed steel plate 30 is covered on the printed circuit board, these openings will just expose the welding pads on the printed circuit board, so that the coating conductive Glue (such as conductive glue) on these pads. The openings 32 on the printed steel plate 30 are arranged in two rows parallel to each other, and can be divided into a first trapezoidal opening 32 a and a second trapezoidal opening 32 b according to the positions of the openings 32 in each row.

As shown in Figure 3, the first trapezoidal opening 32a is located at the left and right ends of each row of openings, and the four adjacent sides of each first trapezoidal opening 32a are respectively the first short side and the first long side parallel to each other. side (ie the upper and lower bottom edges), and the first hypotenuse and the first straight edge (ie the left and right sides). As for the second trapezoidal opening 32b, it is located between the first trapezoidal opening 32a at the left and right ends, and the four adjacent sides of each second trapezoidal opening 32b are respectively the second short side and the second long side parallel to each other (ie upper and lower bottoms), and two second hypotenuses (ie left and right sides).

It should be noted that, for the first trapezoidal opening 32a and the second trapezoidal opening 32b in the same row, the first long side of the first trapezoidal opening 32a is located inside the opening and closer to the other row of openings 32, As for the first short side, because it is located outside the first trapezoidal opening 32 a, it is farther away from the other row of openings 32 . As for the second trapezoidal opening 32b, its second short side is because it is located inside the second trapezoidal opening 32b, so it will be closer to another row of openings 32; The outer side of the second trapezoidal opening 32 b is therefore farther away from the other row of openings 32 .

In addition, for the first trapezoidal opening 32a, the first hypotenuse is located outside the opening, and the first straight side is located inside the opening. As shown in FIG. 3 , the first straight side thereof is closer to the second trapezoidal openings 32 b in the same row, whereas the first hypotenuse is farther away from the second trapezoidal openings 32 b in the same row.

Taking the array structure 10 of 0402 size as an example (refer to FIG. 1 ), there are eight electrodes 18 at the bottom of the array structure 10 , arranged in two rows, and each row has four electrodes 18 . According to the distribution position of each electrode 18 in the row, it can be divided into terminal electrodes 18a located at the left and right ends of each row, and line-along electrodes 18b located between the two terminal electrodes 18a. In this way, as shown in FIG. 4 , soldering pads 42 corresponding to these electrodes 18 are also formed on the provided printed circuit board 40 . There are eight solder pads 42 in total, all of which have a rectangular appearance. They are respectively arranged in two rows to correspond to the above-mentioned terminal electrodes 18 a and line electrodes 18 b, and provide the electrical connection required by the 0402 array structure. Similarly, the solder pads 42 can also be divided into first solder pads 42 a located at the left and right ends of a row and second solder pads 42 b located therebetween according to their positions in each row.

When conducting the conductive adhesive printing process, the above-mentioned printed steel plate 30 can be covered on the printed circuit board 40 first, and then the conductive adhesive layer is coated on the printed steel plate 30 . Through the hollowed-out first trapezoidal opening 32 a and the second trapezoidal opening 32 b , a required conductive adhesive layer can be formed on the upper surface of the pad 42 . As shown in FIG. 4, after the printed steel plate 30 is removed, the first conductive adhesive layer 44a coated on the first welding pad 42a will have the same trapezoidal appearance as the first trapezoidal opening 32a, that is, each first The conductive adhesive layer 44a will also have a first short side and a first long side parallel to each other, and its first long side will be closer to another row of pads 42 because it is located inside the first pad 42a. One short side is farther away from the other row of welding pads 42 because it is located outside the first welding pad 42 a. Similarly, the second conductive adhesive layer 44b coated on the second pad 42b also has the same trapezoidal appearance as the second trapezoidal opening 32b. That is, each second conductive adhesive layer 44b will have a second short side and a second long side parallel to each other, and its second short side will be closer to another row of soldering pads because it is located inside the second pad 42b. As for the second long side of the pad 42 , since it is located outside the second pad 42 b , it is relatively far away from the pads 42 in another row.

After removing the printed steel plate 30 , the surface mount electronic components such as 0402 arrays can be placed on the printed circuit board 40 , and the electrodes of each electronic component can be pressed against the corresponding conductive adhesive layer 44 . Wherein, the terminal electrode 18a of the 0402 array structure 10 is pressed against the first conductive adhesive layer 44a, and the electrode 18b along the line is pressed against the second conductive adhesive layer 44b. Then, by performing a reflow process, the surface mount electronic components can be assembled and fixed on the printed circuit board 40 , and the electrodes in the 0402 array can be electrically connected to the pads 42 through soldering.

In a preferred embodiment, when the rectangular pad 42 made on the printed circuit board 40 has a length of about 20 mils (mil) and a width of 10 mils, and the distance between two adjacent pads 42 in the same row When the distance is 8.8 mils and the distance between the upper and lower rows of pads is 17 mils, the first short side of the first trapezoidal opening 32a can be controlled at about 7.5-12.5 mils, and the first long side can be controlled at about 7.5-12.5 mils. About 11.5~16.5 mils. The second short side of the second trapezoidal opening 32b is about 3.2-8.4 mils, and the second long side is about 8-14 mils. Moreover, no matter the height of the first trapezoidal opening 32 a or the second trapezoidal opening 32 b is greater than the length of the rectangular pad 42 (20 mils). In other words, for the second trapezoidal opening 32b, its second short side is approximately 2/5˜3/5 of its second long side.

Since the second short side of the second trapezoidal opening 32b is only 2/5-3/5 of its second long side, the second conductive adhesive layer coated through the opening 32b will also have the same trapezoidal shape. . For two adjacent rows of welding pads, since the second short side of the second conductive adhesive layer is located at the inner side of the second welding pad 42b, as shown in FIG. 4, the inner surface of the welding pad will only be partially conductive. Adhesive coating. In this way, when the 0402 array structure is placed, even if it is pressed by the electrodes 18b along the line, the situation of extending to both sides will be relatively slight due to the small amount of conductive adhesive located inside the second pad 42b. In the subsequent reflow process, the second conductive adhesive layer 44b is relatively less prone to bridging with adjacent conductive adhesive layers to cause a short circuit. And because of the molten solder, there will be no bridging situation, so the empty soldering situation caused by the surface tension of molten tin in the traditional manufacturing process can also be effectively prevented.

In addition, in this embodiment, the first trapezoidal opening 32a is shifted outward so that there is a larger distance between it and the second trapezoidal opening 32b in the same row. Therefore, as shown in FIG. 4, the first straight edge on the inside of the first conductive adhesive layer 44a will not completely cover the inside of the first pad 42a, but will expose the inside of the first pad 42a. sideline area. That is, when the distance between the first pad 42a and the second pad 42b is 8.8 mils, the first conductive adhesive layer 44a will be shifted to the outside, so that the distance between it and the second conductive adhesive layer 44b The spacing is greater than 8.8 mils. In this way, by increasing the distance between the first conductive adhesive layer 44a and the second conductive adhesive layer 44b, the chance of bridging effect therebetween can be greatly reduced.

Due to the effective prevention of problems such as short circuits and empty soldering, the yield rate of the overall surface mount manufacturing process can be greatly improved. Moreover, because there is no need to spend a lot of labor costs on testing and debugging, this can effectively reduce the relevant manufacturing process cycle and achieve the purpose of increasing production capacity. In addition, because the opening of the steel plate designed by the present invention has a smaller area, the amount of conductive adhesive coated is also smaller, thereby achieving the effect of saving costs.

Although the present invention is illustrated above with preferred examples, they are not intended to limit the spirit and scope of the present invention. Those skilled in the art can easily understand and utilize other elements or methods to produce the same effect. Therefore, modifications made without departing from the spirit and scope of the present invention should be included in the scope defined by the following claims.

Claims (11)

1. A printed steel plate applied to the adhesive manufacturing process on the surface of an electronic component, characterized in that the printed steel plate is used to coat a conductive adhesive layer on the solder pads on the surface of the printed circuit board, and these solder pads are corresponding Contact electrodes of electronic parts are adhered to the surface, and the printed steel sheet has: A plurality of trapezoidal openings, corresponding to the welding pads, conductive adhesive can be coated on the welding pads through the trapezoidal openings; the plurality of trapezoidal openings are arranged in two rows, and each row of the trapezoidal openings is divided into: The first trapezoidal opening is located at both ends of each row of trapezoidal openings, the long side of the first trapezoidal opening is adjacent to the other row of trapezoidal openings, and the short side of the first trapezoidal opening is away from the other row of trapezoidal openings; The second trapezoidal opening is located between the first trapezoidal openings, the short side of the second trapezoidal opening is adjacent to the other row of trapezoidal openings, and the long side of the second trapezoidal opening is away from the other row of trapezoidal openings. 2. The printed steel sheet according to claim 1, wherein the first trapezoidal opening has a straight side and a hypotenuse that are not parallel to each other, and the hypotenuse is farther away from the second trapezoidal opening in the same row , the straight side is closer to the second trapezoidal opening in the same row, and the extending direction of the straight side is perpendicular to the arrangement direction of the row of trapezoidal openings. 3 . The printed steel sheet according to claim 2 , wherein the first short side of the first trapezoidal opening is 7.5-12.5 mils, and the first long side is 11.5-16.5 mils. 4. The printed steel sheet according to claim 2, wherein the length of the second short side of the second trapezoidal opening is 2/5 to 3/5 of the length of the second long side, and the second short side The sides are 3.2-8.4 mils, and the second long side is 8-14 mils. 5. The printed steel sheet according to claim 1, wherein the first trapezoidal opening has a first straight side and a first hypotenuse, and the first hypotenuse is farther away from the second trapezoid in the same row For the opening, the first straight side is closer to the second trapezoidal opening in the same row, and the extending direction of the first straight side is parallel to the arrangement direction of the row of trapezoidal openings. 6. A method for assembling surface mount electronic parts on a printed circuit board with surface mount technology (SMT), characterized in that the bottom of the surface mount electronic parts has a plurality of electrodes arranged in two rows respectively, and these electrodes Including a first electrode located at both ends of each row, and a second electrode located between the two end electrodes, the method at least includes the following steps: A printed circuit board is provided, on which a plurality of welding pads are provided, each corresponding to the plurality of electrodes of the surface mount electronic component, and the plurality of welding pads are also arranged in two rows, including two The first welding pad at the end, and the second welding pad located between the two first welding pads; Coating a conductive adhesive layer on each of the welding pads, wherein the first conductive adhesive layer coated on the first welding pad has a trapezoidal appearance, and each of the first conductive adhesive layers has first short lengths parallel to each other. side and the first long side, the first long side is adjacent to another row of the pads, and the first short side is away from the other row of pads, wherein the second conductive adhesive coated on the second pad The layer has a trapezoidal appearance, and each of the second conductive adhesive layers has a second short side and a second long side parallel to each other, the second short side is adjacent to the other row of pads, and the second long side is away from on the other row of pads; and The surface mount electronic component is placed on the printed circuit board, and each of the electrodes touches the corresponding conductive adhesive layer. 7. The method of claim 6, further comprising: A reflow process is performed to fix the surface mount electronic components on the printed circuit board. 8. The method according to claim 6, further comprising covering a printed steel plate on the printed circuit board before the coating of the conductive adhesive layer on the pad, the printed steel plate has several openings that just expose the surface of the pads, Wherein the several openings of the printed steel plate are arranged in two rows parallel to each other, wherein each row of the openings is divided into: The first trapezoidal openings are located at both ends of each row of openings, each of the first trapezoidal openings has a first short side and a first long side parallel to each other, the first long side is adjacent to another row of openings, and the first trapezoidal openings the first short side is away from the other row of openings, The second trapezoidal openings are located between the first trapezoidal openings, each of the second trapezoidal openings has a second short side and a second long side parallel to each other, the second short side is adjacent to another row of openings, and the second trapezoidal openings are adjacent to each other. The second long side is far away from the other row of openings. 9 . The method according to claim 6 , wherein the length of the second short side of the second conductive adhesive layer is 2/5˜3/5 of the length of the second long side. 10. The method according to claim 6, wherein the first conductive adhesive layer exposes a part of the edge area inside the first pad, and the first conductive adhesive layer and the second conductive The distance between the adhesive layers is larger than the distance between the first welding pad and the second welding pad. 11. A printed circuit board, characterized in that it comprises: a plurality of pads arranged in two rows; A surface mount electronic component has a plurality of electrodes arranged in two rows, and the position of each electrode corresponds to the position of the solder pad; and A plurality of solder layers, which are arranged in two rows to respectively connect the pads and the electrodes, wherein in each row of the solder layers, the distance between each solder layer adjacent to the other row of the solder layer is greater than that of each solder layer The distance between the part of the solder layer that is farther away from another row; the solder layer of each row can be divided into: The first conductive adhesive layer is located at both ends of each row of the solder layer, and the width of the part of each first conductive adhesive layer closer to the other row of conductive adhesive layer is greater than that farther away from the other row of conductive adhesive layer the width of the portion; The second conductive adhesive layer is located between the first solder layers, and the width of each second conductive adhesive layer closer to another row of conductive adhesive layer is smaller than that of the other row of conductive adhesive layer. portion width.

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