Pad and circuit board, electronic device using same

[0001] 1. Technical Field

[0002] The present invention relates to surface mount technology (SMT), and more particularly, to an improved pad used for mounting a surface mounted component (SMC) on a circuit board.

[0003] 2. Description of Related Art

[0004] In recent years, surface mount technology (SMT) is being widely used in electronic device manufacturing. SMT is a method for assembling surface mounted components (SMC) onto the surface of printed circuit boards (PCBs). A pin or solder ball of a SMC is usually smaller than its leaded counterpart because it has either smaller leads or no leads at all. It may have short pins or leads of various styles, flat contacts, a matrix of balls (ball grid arrays, BGAs, for example), or terminations on the body of the component.

[0005] Ball grid arrays (BGA) accommodates the demands of SMT, and resolves the applications with high density, lower thermal resistance, low inductance leads, improved high speed performances, multiple functions, and high I/O count. However, one disadvantage of the BGA is that the solder balls of the BGA cannot flex in the way that longer leads can, and there is only one juncture between the solder balls and the pads, thus the solder joints fracture (solder-off) easily. Another disadvantage is that once the BGA components are soldered, it is very difficult to detect soldering faults, thus, a quality of the soldering cannot be ensured. Pseudo soldering, and excess solder connections occurs frequently in BGA solder process. These disadvantages which limits the application of BGA also occurs in other surface-mount packaging.

[0006] Common pads have different configurations due to varied configurations of the contacts of the electronic elements, such as a circle, a square, a teardrop, and so on. The size of the pads is usually larger than the size of the contacts of the electronic elements corresponding to the pads. When soldering the electronic elements to the circuit board, the contacts of the electronic elements may slide on the pads. As a result, accurate positioning of the electronic elements cannot be assured, pseudo soldering, solder-off, and excess solder connections will also happen.

[0007] What is needed, therefore, is an improved pad capable of accurately positioning the electronic element and not become disconnected from the contacts of the electronic element.

[0008] In accordance with one embodiment, A pad for soldering a contact of a surface mounted component is provided herein. The pad includes a central portion and a plurality of separate extending portions extending from the central portion. All of the extending portions include a free end and a connected end connected to the central portion. A width of the free end is larger than a width of the connected end. A circuit board and an electronic device are also provided.

[0009] Other advantages and novel features of the present pad, circuit board, and electronic device will become more apparent from the following detailed description of preferred embodiment when taken in conjunction with the accompanying drawings.

[0016] The embodiments will now be described in detail below with reference to the drawings.

[0017] FIG. 1 is a partial top view of a circuit board 20 in accordance with a first exemplary embodiment. A pad 10 resides on a surface (not labeled) of the circuit board 20, and is surrounded by a solder resist 30 that also resides on the surface of the circuit board 20. The solder resist 30 extends to a periphery of the pad 10. The pads 10 can be formed on the circuit board 20 by chemical etching etc, and a solder paste may be printed onto the pad 10.

[0018] The circuit board 20 may be a printed circuit board laminate composed of multiple layers of non-conductive material and conductive traces sandwiched together to form a rigid planar structure. The pad 10 is electrically connected to the conductive traces of the circuit board 20 and is configured for mounting a contact of a surface mounted component (SMC, a resistor, a capacitor, an integrated circuit, an image sensor or the like, for example) in order to electrically connect the SMC and the conductive traces of the circuit board 20. The pad 10 may be bare copper, or copper (Cu) electroplated with at least one of gold (Au), silver (Ag), tin (Sn), aluminum (Al) or other conductive metal materials. The pad 10 may also be a conductive body that contains Ag, Au, Cu, iron (Fe), Al, Sn or other conductive metal materials.

[0019] In the present embodiment, the pad 10, by and large, is circular-shaped and its size is equal to or slightly larger than a ordinary circular-shaped pad. The pad 10 includes a square central portion 11 and four separate extending portions 13 extending separately from four sides of the central portion 11. Preferably, the four extending portions 13 are uniformly distributed around the central portion 11. An outline of the extending portion 13 is almost a T-shaped. The extending portion 13 includes a connected end 131 connected to the central portion 11, and a free end 133 with a width W1 larger than a width W2 of the connected end 131.

[0020] As the a plurality of extending portions 13 are uniformly distributed around the central portion 11, in the soldering process, liquid surface tension causes the molten solder to hold the contact of the SMC at the central of the pad 10. The solder resist 30 between every two extending portions 13 can prevent the contact of the SMC from sliding out the extending portions 13 in the soldering process. Therefore, the SMC is capable of being positioned on the surface of the circuit board 20 accurately. Also in the soldering process, the central portion 11 and the extending portions 13, can be automatically filled with the molten solder, thus avoiding solder-off, pseudo soldering, excess solder connections, etc. Furthermore, the longest length of the pad 10 is equal to or slightly larger than an ordinary circular-shaped pad, that is, an actual size of the pad 10 is slightly smaller than an ordinary circular-shaped pad, thus, solder paste can be saved.

[0021] Particularly, when the contact of the SMC is mounted on the pad 10, all the extending portions 13 and the central portion 11 are connected to the contact, thus there are a plurality of junctures between the pad 10 and the contact, thus, an adhesive strength of the joint between the contact and the pad 10 is strengthened. Furthermore, the width W1 of the free end 133 is larger than the width W2 of the connected end 131, if a juncture between one of the extending portions 13 and the contact fractures, the other junctures between the other extending portions 13 and the contact will not be affected, and the joint between the contact and the pad 10 will not fracture.

[0022] In other embodiments, variations can be made to the pad 10. For example, FIG. 2 shows the circuit board 20 including at least a pad 10 in accordance with a second exemplary embodiment. In the embodiment, the pad 10, by and large, is circular-shaped, too. The pad 10 includes a circular central portion 11 and four separate extending portions 13 extending separately from the side of the central portion 11. Preferably, the four extending portions 13 are uniformly distributed around the central portion 11. The outline of the extending portion 13 is almost fan-shaped. The extending portion 13 includes a connected end (not labeled) connected to the central portion 11, and a free end (not labeled) with a width W1 larger than a width W2 of the connected end.

[0023] FIG. 3 shows the circuit board 20 including at least a pad 10 in accordance with a third exemplary embodiment. In the embodiment, the pad 10, by and large, is circular-shaped, too. The pad 10 includes a circular central portion 11 and three separate extending portions 13 extending separately from the side of the central portion 11. Preferably, the three extending portions 13 are uniformly distributed around the central portion 11. The outline of the extending portion 13 is substantially shaped like a fan-blade. The extending portion 13 includes a connected end (not labeled) connected to the central portion 11, and a free end (not labeled) with a width W1 larger than a width W2 of the connected end.

[0024] FIG. 4 is a partial top view of the circuit board 20 including at least four pads 10 thereon in accordance with a fourth exemplary embodiment. In the embodiment, each of the pads 10, by and large, is square-shaped. Each of the pads 10 includes a square central portion 11 and four separate extending portions 13 extending separately from the four corners of the central portion 11. Preferably, the four extending portions 13 are uniformly distributed around the central portion 11. The outline of the extending portion 13 is almost diamond-shaped. The extending portion 13 includes a connected end (not labeled) connected to the central portion 11, and a free end (not labeled) with a largest width W1 larger than a width W2 of the connected end.

[0025] Referring to FIG. 5, the circuit board 20 according to a fifth embodiment includes a pad array 22 with two regular shaped pads 24 and two predeterminedly shaped pads 10. The two pads 10 are disposed diagonally across the pad array 22. The pads 10 are similar to the pads 10 of the circuit board 20 of FIG. 4 except that they have a circular outline. In the embodiment, each of the pads 10, by and large, is square-shaped. Each of the pads 10 includes a square central portion 11 and four separate extending portions 13 extending separately from the four corners of the central portion 11. Preferably, the four extending portions 13 are uniformly distributed around the central portion 11. The outline of the extending portion 13 is almost fan-shaped. The extending portion 13 includes a connected end (not labeled) connected to the central portion 11, and a free end (not labeled) with a width W1 larger than a width W2 of the connected end. It can be easily understood that a proportion between a number of the ordinary shaped pads 24 and a number of the pads 10 can be predeterminedly configured according to need, and the ordinary shaped pads 24 can be circular-shaped, square-shaped, or polygon-shaped pads.

[0026] It should be understood that the number of the extending portions 13 of the pad 10 should be equal to or more than three. The central portion 11 can be polygon-shaped. The number of the extending portions 13 of the pad 10 can be decided as needed and is not limited to the particular embodiments described.

[0027] FIG. 6 is a schematic side view of an electronic device 100 according to an exemplary embodiment. The electronic device 100 includes a circuit board 40 and at least a surface mounted component (SMC) 60. The SMC 60 may be a resistor, a capacitor, an integrated circuit, an image sensor or the like. In the embodiment, the SMC 60 is an integrated circuit in BGA package. A plurality of solder balls 70 are stuck to a bottom of the SMC 60. A plurality of pad 50 resides on the surface of the circuit board 40 in a pattern that matches the solder balls 70.

[0028] Every pad 50 has a central portion (not shown) and a plurality of separate extending portions (not shown) extending from the central portion. The a plurality of extending portions are uniformly distributed around the central portion. All of the extending portion includes a connected end (not shown) connected to the central portion, and a free end (not shown) with a largest width larger than a largest width of the connected end. A solder paste (not shown) is printed onto the pad 50. A solder resist (not shown) also resides on the surface of the circuit board 40, and extends to peripheries of the pads 50.

[0029] In the soldering process, the electronic device 100 is heated, either in a reflow oven or by an infrared heater, causing the solder balls 70 to melt. Surface tension causes the molten solder paste to hold the solder balls and the SMC 60 in alignment with the circuit board 40, at the correct separation distance, while the solder paste cools and solidifies.

[0030] As described above, the SMC 60 is capable of being positioned on the surface of the circuit board 40 accurately. Solder-off, pseudo soldering, and excess solder connections can be avoid. Particularly, an adhesive strength of the joint between the solder balls 70 and the pad 50 is strengthened and hardly fractures. Thus, the reliability of the electronic device 100 is ensured.

[0031] While certain embodiments have been described and exemplified above, various other embodiments will be apparent to those skilled in the art from the foregoing disclosure. The present invention is not limited to the particular embodiments described and exemplified but is capable of considerable variation and modification without departure from the scope of the appended claims.