CN107113963A - Spoke Pads for Improving Self-Alignment and Solderability of Integrated Circuit Packages - Google Patents

Abstract

A center pad or paddle is formed with at least three curved tapers that are symmetrically shaped about an axis radiating from the center of an integrated circuit package that utilizes the surface tension of solder to produce increased rotational alignment forces and increased centering forces during package soldering when aligned to a matching shaped pad on the surface of a circuit board.

Description

Spoke Pads for Improving Self-Alignment and Solderability of Integrated Circuit Packages

technical field

The present disclosure relates to a solder pad, in particular to a solder pad with more than three spokes, which is used in an integrated circuit package and/or a circuit board.

Background technique

One of the many challenges encountered when soldering high wire count components to a circuit board is proper alignment of the chips. Proper alignment is particularly challenging in manual welding projects and can also cause difficulties in automated welding projects.

Brief description of the drawings

Aspects of the present invention are best understood from the detailed description when read in relation to the accompanying drawings. The drawings show various aspects, features, and embodiments of the present disclosure, so it is understood that the illustrated embodiments are representative and not exhaustive in scope. The present disclosure will be described with reference to the drawings, wherein like numerals refer to like components.

Fig. 1 shows a plan view of a plurality of radial axes arranged in a symmetrical distribution around a central point of installation according to an embodiment.

2 shows a top plan view of a pad having at least three solderable lobes, each extending symmetrically along a radial axis, according to one embodiment.

Figure 3 shows a view of the solder pre-fill on the pad as shown in Figure 2.

4 shows a top plan view of pre-filled solder wetting along various radial axes during soldering according to one embodiment.

5 shows a top plan view of a pad with pads rotated to alignment from a mating pad in accordance with one embodiment.

6 shows a top plan view of a pad with off-center pads displaced from mating pads shifted to alignment according to one embodiment.

7 shows a top plan view of a bonding pad with integrated circuit components in unused adjacent space according to one embodiment.

8 shows a top plan view of a pad having straight solder lobes extending symmetrically along radial axes, each solder lobes having a rounded end, according to one embodiment.

9 shows a top plan view of a pad having a plurality of straight solder lobes, each extending symmetrically along a radial axis and having a curved end, according to one embodiment.

10 shows a top plan view of the solder pad having a plurality of straight solder lobes, each extending symmetrically along a radial axis and having a straight end, according to one embodiment.

FIG. 11 shows a top plan view of the solder pad shown in FIG. 8 with each solder lobe having a straight end according to one embodiment.

12 shows a top plan view of a triangular pad with corners extending symmetrically along three radial axes from the center of the pad according to an embodiment.

13 shows a top plan view of a bonding pad having at least three solderable tips, each extending symmetrically along a radial axis, according to one embodiment.

14 shows a top plan view of a solder pad with solderable tips extending symmetrically along multiple radial axes, according to one embodiment.

15 shows a perspective view of frictional forces resisting wetting of solder on a pad according to one embodiment.

16 shows a perspective view of gravity affecting wetting of solder on a pad according to one embodiment.

17 shows a perspective view of surface tension affecting solder wetting on a pad according to one embodiment.

18 shows a perspective view of intermolecular/atomic attraction forces affecting wetting of solder on a pad according to one embodiment.

19 shows a perspective view of a solder pad having a radially central pad portion and force interactions affecting solder wetting on the pad, according to one embodiment.

20 shows an exploded perspective view of an assembly (cross-sectional view) of a solder pad with a radially central pad, solder, and a circuit board with a mating pad with a radially central pad, according to an embodiment.

21 shows a perspective view of an assembly (cross section) of a solder pad with a radially central pad, solder, and a circuit board with a mating pad with a radially central pad, according to one embodiment.

Figure 22 shows a cross-sectional side view of an assembly, solder, and circuit board according to one embodiment.

detailed description

This document describes a method of forming the center pad of a chip and the corresponding circuit board pad to realign surface tension and intermolecular forces to help reorient the stress more toward a vertical orientation with a radial axis Extends from a central point on a pad. The realignment of surface tension and intermolecular forces creates a rotational and positional centering effect on the IC chip based on the balance of forces distributed around the periphery of the pad. According to various embodiments of the present invention, the described spoke pad apparatus, system and method are for overcoming the above-mentioned deficiencies of conventional common types of pads, so as to improve the self-alignment and soldering of integrated circuit packages and/or circuit boards sex. More specifically, the described embodiments provide at least one spoke pad shaped with more than three curved cones, symmetrical in shape about an axis radiating from the center of the integrated circuit package. Solder wetting, intermolecular forces, and surface tension help to apply force to surface mount IC components and help center them. The intermolecular forces and surface tension involved in proper wetting of the extent to which solder flows across the surface of a pad are to help balance the forces between surface mount components and pads to have a balance of forces. The center point, which has the remaining effect of centering the component relative to the pad.

Integrated circuit (IC) packages with larger pad counts are particularly difficult to align. They sometimes have a right rectangular center pad that helps transfer heat from the IC to the board and assists in alignment of components. The problem with a rectangular central pad is that intermolecular forces and surface tension tend to align themselves along the edges of the pad, and with a rectangular central pad the edges are oriented such that at all Only a minimal amount of rotational leverage is provided on the above assembly. Orienting the intermolecular forces and surface tensions perpendicular to the perimeter of the corresponding radial cones will allow those forces to be applied to the cone pads, acting as a lever to rotationally align the assembly about a central point. A right rectangular pad does not provide a good visual alignment of how much solder is needed for the pre-fill of the center pad to solder the component to the printed circuit board. Furthermore, the right rectangular pads exert only a minimal amount of force to center the chip and, because of their shape, require a more precise amount of solder for the centering to work.

See the detailed description of the embodiments shown in the drawings. The following detailed description, with respect to the accompanying drawings, constitutes a part hereof, and shows by way of illustration specific embodiments in which the disclosure may be practiced. Various aspects of the illustrated embodiments will be described using the terminology of those skilled in the art to convey the substance of their accomplishments to others skilled in the art. However, the embodiments described herein may be practiced in only some of the described aspects. For purposes of explanation, specific numbers, materials and configurations may be set forth in order to provide a thorough understanding of the illustrated embodiments. However, the embodiments described herein may be practiced without these specific details. In other instances, well-known features are omitted or simplified in order to avoid obscuring the illustrated embodiments. Furthermore, various operations may be described as multiple discrete operations so that an understanding of the embodiments described herein may be helpful; however, the order of description should not be construed to mean that these operations must be performed in accordance with order. In particular, these operations do not have to be performed in the order presented.

Throughout the specification and drawings, the following terms have at least the relevant meanings as detailed herein, unless the context clearly states otherwise. The following meanings are not intended to limit these terms, but merely to provide illustrative examples of their usage. The meanings of "a" and "the" may include both the singular and the plural. "One embodiment" or "an embodiment" in the specification means that a specific feature, structure or characteristic described in relation to the embodiment is included in at least one embodiment of the present disclosure, but need not be included in the present disclosure in all examples. As used herein, the term "solder" generally refers to any of various alloys that are melted and applied to a joint between two metal objects to join them without heating the objects to their melting point. As used herein, the term "pad" generally refers to a shaped solderable area that provides a solder connection between a component and a board. In addition, today's IC chips have "matching pads," which constitute separate pads on both the IC chip and the circuit board for mating with each other. The term "surface tension" as used herein generally refers to the attractive force exerted on surface molecules of a liquid by the subsurface molecules helping to pull the surface molecules towards the bulk of the liquid and causing the liquid to assume a shape with minimal surface area . Therefore, surface tension is an elastic like force that exists on the surface of an object, especially a liquid surface, and helps to minimize the surface area, which is caused by the asymmetry of the intermolecular forces between the surface molecules. As used herein, the term "cohesion" generally refers to the molecular forces between particles within an object or substance to hold them together. The term "wetting" as used herein generally refers to dissolution, which occurs when hot molten solder dissolves and melts the surfaces being soldered, forming a new alloy of a mixture of solder and the metal of the original surface. Wetting is used to describe the extent to which a molten substance will help bond with another metal by forming an intermolecular bond at a surface junction. As used herein, the term "rotational alignment" generally refers to the alignment of a component with a set of radial axes extending from the center of a component to a matching set of radial axes extending from the center of the mounting location such that the two The axes of the pads are aligned with each other. The term "central alignment" used herein generally refers to the alignment of the center of a component and the center of its installation location.

Referring to FIG. 1 , a plan view of a plurality of radial axes arranged in a symmetrical distribution around a central point of installation is shown according to one embodiment. To facilitate manual soldering of high pad count chips, the central pad can be shaped in such a way that it has more than three rounded symmetrical cones extending from a smaller central area. Referring to FIG. 2 , a top plan view of a pad having more than three solderable lobes is shown according to one embodiment. Each weldable flap extends symmetrically along a radial axis. These cones are symmetrical about spoke-like radial axes distributed equidistantly around the center of the assembly (see eg Figures 1 and 2). These equidistant tapers increase the edge length of the central pad and are formed along the axis.

Referring to FIG. 3 , a top plan view of pre-filled solder on the pad is shown according to one embodiment. Solder may be pre-filled into the central area of the spoke pads on the board. The central area of the central pad acts as a gauge for the amount of solder that should be placed on the pad (see eg: Figure 3). An assembly with a mating spoke-shaped pad as described above is placed on the pad with the least amount of rotational misalignment. At this point there is a situation where heating of the solder on the central pad and heating of the component pad will cause the solder to bond the component to the board from the center.

Having the correct amount of solder for the joint will help judge the quality of the soldered joint. When a solder joint is being created, the oxide layer on the metal surface being bonded prevents intermolecular attraction from occurring and prevents the solder from wetting completely across the surface of the pad. Proper wetting of the solder to the component leads as well as the board is an indicator that the conditions for producing a solder joint are sufficient to produce a high quality intermolecular bond between the metal and the solder on the pads of the board and the component.

With sufficient soldering conditions (including surface cleanliness and heat), the solder will wet over the entire surface of the pads on boards and components, and the surface tension of the solder and the intermolecular interactions of the solder will be established A balance of opposing forces between forces. This balance of opposing forces is visually observed when the amount of solder is sufficient to form a concave fillet between the surfaces being joined, wherein the solder flows smoothly into the surfaces. The concave fillet will orient itself perpendicular to the edges of the metal surfaces being soldered, such as pads on the components and boards.

When excess solder is used to create a solder joint, the surface of the solder joint becomes convex and protrudes outward like a bubble. In this case of excess solder, the detection of whether the solder wets smoothly onto the surface of the board being soldered cannot be accomplished by standard visual inspection. The presence of excess solder thus hinders the detection of solder joint defects due to improper heating or oxidized surfaces. More specifically, if there is improper heating or oxidation, the solder joint may be bad but still go undetected due to excess solder.

Referring to FIG. 4 , a top plan view of pre-filled solder wetting along various radial axes during soldering is shown, according to one embodiment. As the component moves down toward the board, the solder will flow or wet out the center evenly along the cone, creating a solder fillet between the component cone and the mounting pad cone (see eg: Figure 4) . The solder fillet is centered along the radial axis passing through the center of the cone, the surface tension and intermolecular forces of the pad and solder cause a rotational force (see e.g.: FIG. 5 ) which pulls and and/or rotate the spikes on the assembly to align with the matching spikes on the plate.

Referring to FIG. 6 , there is shown a top plan view of a pad with offset off-center plurality of pads from a mating pad, wherein the offset plurality of pads are shifted into alignment, according to one embodiment. The rotational force along the radial axis results in both a rotational alignment force and the force interaction between all of the cones resulting in a centering alignment force (see eg Figure 6).

Referring to FIG. 7 , there is shown a top plan view of a bonding pad with integrated circuit components in unused adjacent space, according to one embodiment. The radially tapered shape of the central pad creates some empty space on the board below the assembly where circuit connections such as vias can be placed. This extra space can lead to a tighter component density on the board (see eg: Figure 7).

Furthermore, when using a central pad with multiple radial cones, an important chip misalignment pointer feature can be added to the chip. For example, in one embodiment, when an odd number of cones is used for the center pad for a rectangular IC package (or any number of cones that do not match the number of sides of the chip) , an index tip cone provides alignment. More specifically, the index tip is aligned so that the index tip is centered in the defined relative relationship of pin 1 to a central pad of the corresponding alignment and points perpendicular to the edge of the chip side The radial axis coming out of the center of the chip is on the board. Then, as solder flows to the central pad, the chip will rotate to align the spikes on the chip with the spikes on the board relative to the central pad. More specifically, when pin one is in the correct position, the IC chip will self-align to the correct position relative to all other pads around the outside of the IC chip. In one example, if the chip is initially placed with pin 1 not in place, then as the solder flows with the tip on the center pad on the board and the IC chip aligns itself , the IC chip will rotate to a position that is out of alignment with the chip outline on the board, and will quickly reveal apparent misalignment, providing a clear indication that pin 1 of the IC chip is misaligned.

Variations of the layouts depicted in Figures 2, 8 to 14 are intended to show how changes in the pad shape can result in slight changes in the characteristics of solder wetting or flow rate, and as the solder moves along the tapered pad. Changes in the orientation of intermolecular forces and surface tension due to wetting. More specifically, the change in shape of the cone can affect solder wetting or flow rate, direction of force over time, rate of movement of the component over time, and overall solder flow direction. The sharpened cone (see eg Figures 12-14) represents a linearly decreasing pad area for solder inflow and has an edge oriented linearly with the axis. Conical shapes that include arcs (see eg, Figures 2, 8, and 9) can vary the force applied to the solder over time as the solder wets along the edges of the cone, from a linearly varying force to is a nonlinear changing force.

Referring to FIG. 8 , a top plan view of a pad having a plurality of straight solder lobes extending symmetrically along a plurality of radial axes is shown in accordance with one embodiment. According to an embodiment, each weld lobe has a rounded end. Furthermore, the increased surface area of each of the solder fillets below the central pad acts like a fin on a heat sink and significantly increases the contact area between the central pad and the surrounding air. This results in more heat transfer from the solder to the air under the chip. This heat transfer improvement applies to each of the various spoke pad layouts shown in FIGS. 2, 8-14.

Referring to FIG. 9 , there is shown a top plan view of a pad having a plurality of straight solder lobes, each of which extends symmetrically along a radial axis and has an arcuate end, according to one embodiment.

Referring to FIG. 10 , there is shown a top plan view of the solder pad having a plurality of straight solder lobes, each solder lobe extending symmetrically along a radial axis and having a straight end, according to one embodiment.

Referring to FIG. 11 , a top plan view of a solder pad is shown, each solder lobe having a straight end, according to one embodiment.

Referring to FIG. 12 , a top plan view of a pad is shown according to an embodiment. The corners of the triangular pad of the pad extend symmetrically along three radial axes from the center of the pad portion. The simplest form of radial arrangement of the cones is a triangle, since this represents the fewest number of radial axes necessary to achieve the desired centering effect.

Referring to FIG. 13 , there is shown a top plan view of a pad having more than three solderable cones, each solderable cone extending symmetrically along a radial axis, according to one embodiment. The triangular pad shown in Figure 12 can be modified as shown in Figure 13 by pulling in the sides and increasing the length of its edges in the radial axis. Increasing the length of the edge along an axis means that the surface tension of the solder will be more aligned with that axis.

Referring to FIG. 14 , there is shown a top plan view of a solder pad having a solderable tip symmetrically extending along a radial axis, according to one embodiment.

Various alignment forces play a role in the movement or alignment of a component during the welding process. The four main alignment or solder wetting forces include gravity (see eg, Figure 16), friction (see eg, Figure 15), surface tension (see eg, Figure 17), and intermolecular/interatomic attraction (see eg, Figure 17). See eg: Figure 18). These solder wetting forces combine in a solder joint to determine how the solder will wet along the surface of a pad (see eg FIG. 19 ). The combination of these solder wetting forces has a directional component relative to the solder, component, and board. Two of the forces (surface tension and friction) have a negative component that hinders solder wetting. The third force, gravity, may have a negative or positive effect, depending on the orientation of the components. For surface mount components, gravity will be a positive force. The fourth force (intermolecular forces) generally has the effect of pulling the solder along the surface, thus having a positive effect on solder wetting. In many configurations, the attractive interatomic or intermolecular force component is one of the strongest force components.

Referring to FIG. 15 , a perspective view of frictional forces resisting wetting of solder on a pad is shown in accordance with one embodiment.

Referring to FIG. 16 , a perspective view of a solder pad is shown using a number of potential gravitational forces affecting solder wetting according to one embodiment.

Of the solder wetting forces indicated, two are reversible. Specifically, the reorientable solder wetting forces are surface tension (see eg: Figure 17) and intermolecular forces (see eg: Figure 18). The intermolecular forces and surface tension involved in proper wetting of the extent to which solder flows across the surface of a pad help to balance the forces between surface mount components and pads so that the forces balance to a central point The remaining effect of is the centering of the component relative to the pad. The shape of the pad has a limiting effect on the forces involved in solder wetting. The shape of the pad will serve to redirect the forces and thereby the direction in which those forces are applied to the assembly.

Referring to FIG. 17 , a perspective view of surface tensions affecting solder wetting on a pad is shown in accordance with one embodiment.

Referring to FIG. 18 , a perspective view of a plurality of intermolecular/atomic attractions affecting the wetting of solder on a pad is shown in accordance with one embodiment. The edge of a pad on a component acts as a boundary for intermolecular/interatomic attraction pulls. Solder does not wet beyond the pad, so in most embodiments the shape of the pad edge limits the intermolecular/interatomic attractions. In a typical circular center pad on a component, the force would be more aligned along an outwardly facing axis and would not provide a rotational effect as the solder wets in progressively because the edges of the pad are parallel to the center. In the described embodiment of the radially central pad, the forces are aligned to allow solder wetting down the length of the pad and then wetting out perpendicular to the radial axis.

In one embodiment, the generation of the pad edge can be achieved by plotting the relative positions of the two input signals with respect to the center of the pad. In one embodiment, the first input signal indicates the current angular position of the next point derived from a point moved around a central point. A signature wave can be used to generate the rotation of the point about a central point (0,0) in polar coordinates where the angle is measured in radians.

The second input signal can represent a signature wave that can be used to change the radius of the rotation point as the rotation point rotates about the center point. The number of lobes produced on the central pad can be derived from the formula:

Number of lobes = radius modulation frequency / rotation frequency

For example: if the point rotates about a central axis at 1 revolution per second, and the radius of the point is to move in and out along the radius using a sine wave pattern of three waves per second, then a three-lobed A central pad is created.

In many embodiments, circuitry mates to a plurality of pads on the assembly. However, in at least one embodiment, multiple pads of the same relative size are compatible as long as the number of pads with the largest number of lobes is a multiple of the number of pads with the fewest lobes. Thus, a pad with three lobes can be soldered to a pad with six, nine, twelve, fifteen, or other total lobes that are multiples of three.

Referring to FIG. 19 , a perspective view of a solder pad having a radially central pad portion shows the interaction of forces affecting wetting of solder on the pad, according to one embodiment.

In one embodiment, the central portion of the radial pad can be altered to limit intermolecular/interatomic forces and to form a gap along the edge of the pad as the solder wets out of the edge of the pad. A balanced tension.

The direction of force and tension depend on the shape of the solder and the shape of the pad. As solder flows off the edge of the pad, forces align perpendicular to the edge and create a balance and tension between positive (gravity and atomic attraction) and negative (surface tension and friction) forces. The tension of the various forces will be aligned towards the edge of the pad as the pad shape dictates the direction of solder pull or flow based on gravity and atomic attraction. Surface tension and friction will always pull inward and resist movement of the solder in an outward direction.

Referring to FIG. 20 , an exploded perspective view of an assembly (cross section) with a pad with a radially central pad, solder, and a circuit board with a mating pad with a radially central pad is shown, according to one embodiment.

Referring to FIG. 21 , an exploded view of an assembly (cross section) with a pad with a radially central pad, solder, and a circuit board with a mating pad with a radially central pad is shown, according to one embodiment.

Referring to Fig. 22, a side view in cross section of a component soldered to the circuit board is shown. The larger pad attached to the component and board, drawn on the left, is a matching central pad with a A radial pattern of petals. The smaller pads to the right of the drawing (on the component and on the circuit board) represent the integrated circuit and the number of pads corresponding to the component mounting footprint, around the perimeter of the component and its corresponding The distribution of the mounting position on the circuit board.

While specific embodiments have been shown and described herein, various alternatives and/or equivalents may be substituted for the specific embodiments described without departing from the scope of the present disclosure. This application is intended to cover any adaptations or variations of the embodiments discussed herein.

Claims (10)

1. A pad layout comprising: a central pad; and at least three radial lobes, coupled to said central pad, arranged radially equidistant from said central pad to produce an increased rotational pair by increasing the ratio of the amount of edge of the pad The rotational alignment force is increased relative to the alignment force associated with the central pad alone. 2. The solder pad layout of claim 1, wherein said central pad portion includes a central pre-filled area, said central pre-filled area serving as a pre-filled container or gauging area for pre-filled solder to improve soldering of a package sex. 3. The solder pad layout of claim 1, wherein the at least three radial lobes comprise a plurality of tapered pads that serve as expanded reservoirs for solder to flow in or to allow placement of packages onto the board. 4. The bonding pad layout of claim 1, wherein the at least three radial lobes comprise a plurality of pointed pads that move along the One edge of the alignment is provided to provide a rotational alignment force that increases as the solder wets from the center of the package outward. 5. The solder pad layout of claim 1, wherein said at least three radial lobes comprise a plurality of tapered pads, said tapered pads extending outwardly and becoming narrower as the solder wets outward to a progressively smaller A storage area provides centering. 6. The bonding pad layout of claim 1 , wherein the at least three radial lobes comprise a plurality of pointed pads based on their orientation in a pattern extending outward from the very center of the chip Provides focus. 7. The pad layout of claim 1 , wherein said at least three radial lobes comprise a plurality of tapered pads increasing surface area along the edge of a solder fillet on said central pad , allowing more heat to transfer from the solder to the air beneath a component chip. 8. The bonding pad layout of claim 1 , wherein the bonding pad layout having the central portion and the at least three radial lobes is reduced by a factor relative to a comparable circular or rectangular bonding pad The overall weight of the package, board, and solder used to secure a component to a circuit board. 9. The pad layout of claim 1, wherein said pad layout having said central portion and said at least three radial lobes is relative to a comparable pad layout having at least the same width and/or height. Rectangular or circular pads with at least the same diameter use less copper and use less solder on a final product board and assembly, resulting in reduced material costs and/or increased material recovery. 10. A radial pad comprising: a central pad or paddle; and Three or more curved cones, symmetrical in shape with at least three axes radiating from the central pad, to generate increased soldering during package soldering when aligned to a matingly shaped pad on the surface of a circuit board Rotational alignment and increased centering.