LED device and wire bonding method

Abstract

The application provides an LED device and a wire bonding method, which comprise a substrate, an LED chip, a bonding wire and an encapsulating glue. The substrate has a pad. The LED chip is fixed on the substrate and located at one side of the pad. The LED chip has a top surface electrode. The top surface electrode is electrically connected with the pad based on the bonding wire. The LED chip and the bonding wire are encapsulated based on the encapsulating glue. The bonding wire comprises a first segment, a second segment and a third segment which are connected in sequence. The first end of the first segment is bonded on the pad. The first segment and the second segment are connected based on a round corner. The connecting position of the second segment and the third segment is located directly above the top surface edge of the LED chip. The end of the third segment is bonded on the top surface electrode. By adjusting the starting point of the BSOB wire bonding process to the pad of the substrate, the arc height of the bonding wire can be reduced under the precondition that the internal stress between the bonding wire and the gold ball will not be too large, so as to meet the actual use requirements.

Description

Technical Field

[0001] This invention relates to the field of LED technology, specifically to an LED device and a wire bonding method. Background Technology

[0002] With the development of technology, sensing devices used in wearable devices are becoming increasingly miniaturized. This means that components such as substrates, encapsulation layers, and chips need to be miniaturized. At the same time, there are higher requirements for the accuracy of sensing devices, namely, higher brightness of LED chips. However, due to the limitations of existing LED chip manufacturing processes, existing high-brightness chips are characterized by large size. Therefore, when using the conventional BSOB wire bonding method, the gold wire curvature is easily deformed during the encapsulation process. In addition, during the wire bonding process, due to the large chip size, the chip edge is prone to touching the gold wire. Summary of the Invention

[0003] To address the issue of high gold wire arc height caused by existing BSOB wire bonding methods, this invention provides an LED device and wire bonding method that adjusts the starting point of the BSOB wire bonding process to the substrate pads. This reduces the bonding wire arc height while ensuring that the internal stress between the bonding wire and the gold ball is not excessive, thus meeting practical application requirements.

[0004] Accordingly, the present invention provides an LED device, including a substrate, an LED chip, bonding wires and an encapsulating colloid, wherein the substrate has pads, the LED chip is fixed on the substrate and located on one side of the pads, the LED chip has a top electrode, the top electrode is electrically connected to the pads based on the bonding wires, and the LED chip and bonding wires are encapsulated based on the encapsulating colloid.

[0005] The bonding wire is characterized in that it comprises a first segment, a second segment, and a third segment connected in sequence;

[0006] The first end of the first segment is bonded to the pad, and the angle between the first segment and the top surface of the pad away from the LED chip is α.

[0007] The first segment and the second segment are transitioned based on rounded corners, and the angle between the first segment and the second segment toward the LED chip is b;

[0008] The connection point between the second and third segments is located directly above the top edge of the LED chip;

[0009] The end of the third segment is bonded to the top electrode, and the angle between the third segment and the top surface of the top electrode toward the LED chip is c.

[0010] In an alternative embodiment, the middle portion of the first segment has a first arch that is away from the direction of the LED chip.

[0011] In an alternative embodiment, the middle portion of the second segment has a downward-facing second arch.

[0012] In an optional implementation, the height of the LED chip is h, the height of the highest point of the bonding wire is less than or equal to 1.5h, and the height of the highest point of the bonding wire is greater than h.

[0013] In an optional implementation, the distance between the connection point of the second segment and the third segment and the top surface of the chip is greater than the wire diameter of the bonding wire.

[0014] In an optional implementation, the height of the LED chip is h, the distance from the connection position of the second segment and the third segment to the top surface of the chip is less than or equal to h / 2, and the distance from the connection position of the second segment and the third segment to the top surface of the chip is greater than or equal to h / 6.

[0015] In an optional implementation, the fillet angle at the connection point between the first segment and the second segment is in the range of [80°, 100°].

[0016] In an optional implementation, the distance between the chip and the pad is 90 micrometers to 1050 micrometers.

[0017] In an optional implementation, the included angle α ranges from 80°. <a<110°。

[0018] In an optional implementation, the included angle c ranges from 8°. <c<25°。

[0019] In an optional implementation, the width of the LED chip is 2 to 2.5 times the distance from the chip electrode to the edge of the chip.

[0020] In an optional implementation, the angle d between the second segment and the horizontal plane ranges from 8° to 25°.

[0021] Accordingly, the present invention also provides a wire bonding method for bonding the bonding wire between the top electrode and the corresponding pad in the LED device, comprising:

[0022] Solder balls are attached to the top surface of the top electrode;

[0023] The lead end of the bonding wire is melted into a gold ball using a wire nozzle and then bonded to the pad.

[0024] By releasing the wire and moving the bonding wire along a preset trajectory based on the wire nozzle, the first segment, the second segment, and the third segment are formed respectively;

[0025] After bonding the end of the bonding wire onto the solder ball by means of a capillary, the bonding wire is cut off.

[0026] In summary, the present invention provides an LED device and a wire bonding method. During processing, due to the height difference between the pad and the top electrode, setting the starting point of the BSOB wire bonding process at the pad allows the substantially vertical front section of the bonding wire to maintain a certain length allowance, which prevents excessive bonding internal stress between the bonding wire and the pad; accordingly, the reduction of the loop height of the bonding wire does not have a great influence on the bonding internal stress between the bonding wire and the pad, ensuring the structural stability of the bonding wire. By setting the end point of the BSOB wire bonding process on the top electrode, the solder ball on the top electrode can well fix the end section of the bonding wire located in the area enclosed by the contour of the LED chip, preventing the connecting position of the second segment and the third segment from touching the LED chip. When the substrate is deformed by heat, due to the existence of the first curved arch, the rounded corner and the second curved arch, when the substrate deforms, the rounded corner swings away from the center of the circle, the second curved arch is subjected to upward stress, the depression of the second curved arch buffers the stress, the depression gradually becomes gentle to adapt to the deformation process of the substrate, and the overall height of the bonding wire does not change greatly, thereby ensuring that the bonding wire does not touch the packaging mold, and ensuring the smooth molding of the packaging colloid and the smooth processing of the LED device. Description of Drawings

[0027] Figure 1 is a schematic cross-sectional structural view of the LED device according to an embodiment of the present invention.

[0028] Figure 2 is a flowchart of the wire bonding method according to an embodiment of the present invention. Detailed Description of Embodiments

[0029] Figure 1 shows a schematic cross-sectional structural view of the LED device according to an embodiment of the present invention.

[0030] The present invention provides an LED device, comprising a substrate 1, an LED chip 3, a bonding wire 4 and a packaging colloid, wherein the substrate is provided with a pad 5, the LED chip 3 is fixed on the substrate 1 and located on one side of the pad 5, the LED chip 3 is provided with a top electrode, the top electrode is electrically connected to the pad 5 via the bonding wire 4, and the LED chip 3 and the bonding wire 4 are packaged via the packaging colloid.

[0031] Specifically, the packaging colloid is used for packaging the LED chip and connecting wires, the height of the chip on the sensing device is h, the height of the packaging layer 6 is H, the constraint relationship between H and h is: 1.5h<H<4h, the value range of H is: 200μm<H<600μm, in order to avoid affecting the schematic view, in the accompanying drawings Figure 1 is not shown.

[0032] The bonding wire comprises a first segment AB3, a second segment B3C, and a third segment CD connected in sequence;

[0033] Specifically, the first end of the first segment AB3 is bonded to the pad 5, and the angle between the first segment AB3 and the top surface of the pad 5 away from the LED chip is α; the middle of the first segment AB3 has a first arch 6 away from the LED chip 3; since the wire nozzle is always facing downward, after the wire nozzle melts the first end of the bonding wire 4 into a gold ball, the direction of the bonding wire 4 brought out from the gold ball is close to perpendicular to the top surface of the pad 5; in this embodiment of the invention, according to the driving of the wire nozzle, the required trajectory of the bonding wire 4 is formed. According to the design of this embodiment of the invention, a first arch 6 structure is formed in the first segment AB3. The first arch 6 is concave in the direction away from the LED chip 3. Specifically, the forming mechanism and effect of the first arch 6 will be explained later in conjunction with the overall structure of the bonding wire 4.

[0034] Specifically, the first segment AB3 and the second segment B3C are transitioned based on rounded corners B1-B3, and the angle between the first segment AB3 and the second segment B3C toward the LED chip is b. Specifically, the first segment AB3 and the second segment B3C are transitioned based on rounded corners B1-B3. Therefore, in actual implementation, the bending point at point B shown in the figure will not occur. The connecting rounded corners of the first segment AB3 and the second segment B3C pass through points B1, B2 and B3 in sequence.

[0035] Specifically, the second segment B3C has a downward-facing second arch 7 in the middle, and the connection position between the second segment B3C and the third segment CD is located directly above the top edge of the LED chip; specifically, the two ends of the second segment B3C are essentially bonding wires connecting the end of the first segment AB3 and the beginning of the third segment CD; by adjusting the length of the second segment B3C, the tension between the first segment AB3 and the third segment CD can be adjusted; in this embodiment of the invention, to avoid excessive internal stress between the first segment AB3 and the gold ball, the length of the second segment B3C should not be too short to avoid pulling the first segment AB3; correspondingly, to avoid the connection position between the third segment CD and the second segment B3C being too close to the top surface of the LED chip, the length of the second segment B3C should not be too long, so as to prevent the second segment B3C from being too long and causing its weight to lower the height of the beginning of the third segment CD, and at the same time, to avoid the second segment B3C from being too long and causing the bottom height of its second arch 7 to be too low. In practice, while ensuring the height of point C, the specific length of the second segment B3C is not quantitatively limited. However, in this embodiment of the invention, due to the limitations of the position of point C directly above the top edge of the LED chip 3, the distance between point C and the top surface of the LED chip 3, and the angle of a, the length of the second segment B3C is correspondingly limited in actual implementation. If the length of the second segment B3C is too small, the angle of a will not meet the requirements. If the length of the second segment B3C is too long, the support of the third segment CD will be insufficient, and point C will be lowered.

[0036] Specifically, the end of the third CD segment is bonded to the top electrode, and the angle c between the third CD segment and the top surface of the top electrode towards the LED chip is . Specifically, since the wire feed needs to cut the bonding wire on the solder ball of the top electrode, the direction of the cut is nearly perpendicular to the direction of the wire feed. Therefore, the angle c between the bonding wire on the top electrode and the top electrode is a small angle. After the bonding material cures, the end of the third CD segment is essentially fixed to the top electrode; therefore, the third CD segment is actually fixed by the solder ball of the top electrode.

[0037] Based on the above-described bonding wire structure, the first end of the first segment AB3 is fixed to the gold ball of the pad 5, and the end of the first segment AB3 is located above the beginning of the first segment AB3. The first segment AB3 can be regarded as a flexible rod structure with one end fixed. The end of the third segment CD is fixed to the solder ball of the top electrode, and the beginning of the third segment CD is located directly above the top edge of the top electrode. The third segment CD can be regarded as a flexible rod with one end fixed to the solder ball. The second segment B3C can be regarded as a flexible rod structure with both ends connected to the end of the first segment AB3 and the beginning of the third segment CD.

[0038] Since the bonding between the beginning of the first segment AB3 and the pad is extremely strong and reliable, and the pad has a strong fixing effect on the beginning of the first segment AB3, the beginning of the first segment AB3 can be regarded as a fixed and unchanging structure. Similarly, the bonding between the end of the third segment CD and the top electrode is extremely strong and reliable, and the top electrode has a strong fixing effect on the end of the third segment CD. Therefore, the end of the third segment CD can be regarded as a fixed and unchanging structure. Accordingly, the attitude changes of other positions of the first segment AB3 and the attitude changes of other positions of the third segment CD are related to the second segment B3C.

[0039] The forces exerted by the second segment B3C on the third segment CD and the first segment AB3 are F1 and F2, respectively (the angle of the force is actually the tangential direction, which is difficult to represent due to its small size). Figure 2 (Using similar directions for identification); First, the wire nozzle generates fillets B1-B3 through the trajectory control of the bonding wire. Then, the first end of the second bonding wire is connected to point B3. The second segment B3C participates in the bending of fillets B1-B3 at point B3. Correspondingly, since the first segment AB3 is not a rigid rod but a flexible rod, a first arch 6 is formed at the first segment AB3. The existence of the first arch 6 and fillets B1-B3 utilizes the force generated by their bending to support the first end of the second segment B3C at point B3. Then, since the length of the third segment CD is relatively short, the first end of the third segment CD is maintained at point C by the fixing force between the end and the top electrode. When the weight of the second segment B3C does not exceed the preset range, the position of point C hardly changes.

[0040] In light of practical considerations, the LED device structure provided in this embodiment of the invention, during processing, due to the height difference between the pad and the top electrode, sets the starting point of the BSOB bonding process at the pad. This allows the near-vertical front section of the bonding wire 4 to maintain a certain length allowance, preventing excessive bonding internal stress between the bonding wire 4 and the pad. Correspondingly, the reduction in the arc height of the bonding wire 4 will not significantly affect the bonding internal stress between the bonding wire 4 and the pad, ensuring the stability of the bonding wire 4 structure. Setting the ending point of the BSOB bonding process on the top electrode allows the solder balls on the top electrode to effectively fix the end section of the bonding wire 4 within the area enclosed by the LED chip 3 outline, preventing the connection positions of the second segment B3C and the third segment CD from contacting the LED chip.

[0041] Specifically, based on actual implementation statistics, the height of the LED chip 3 is h, and the highest point of the bonding line 4 (see attached figure) Figure 1The height of point B3 (i.e., the height of the highest point B3 from the top surface of the substrate) is less than or equal to 1.5h, and the height of the highest point of the bonding line is greater than h. Specifically, the height of point B2, the midpoint of the rounded corner between the first segment AB3 and the second segment B3C, is greater than or equal to the height of the light-emitting chip 3. By limiting the height of point B2, the height of point B3 will not drop below a threshold during substrate deformation, thus preventing the second arch 7 from contacting the side of the LED chip.

[0042] Accordingly, in order to leave an appropriate positional margin, the height of the LED chip is h, and the maximum height of the highest point of the rounded corner at the connection position of the first and second segments (i.e., the height of point B3) is 1.5 times the height of the light-emitting chip.

[0043] Specifically, in order to leave an appropriate margin, the connection position of the second segment B3C and the third segment CD is at a height greater than the diameter of the bonding wire from the top surface of the chip.

[0044] Specifically, the bonding wire used in this embodiment of the invention has a wire diameter of 25 μm, and correspondingly, the connection position of the second segment B3C and the third segment CD is at a height greater than 25 μm from the top surface of the chip.

[0045] Furthermore, the connection point of the second segment B3C and the third segment CD is at a height less than or equal to h / 2 from the top surface of the chip, and the connection point of the second segment and the third segment is at a height greater than or equal to h / 6 ​​from the top surface of the chip. This arrangement ensures that the probability of the connection line touching the chip is reduced during thermal deformation of the substrate.

[0046] Specifically, since the bonding position of the top electrode needs to provide sufficient support for the third CD segment, and the bonding strength between the end of the third CD segment and the top electrode is not high due to the cutting of the wire nozzle during conventional processing, in order to ensure the morphological stability of the third CD segment and to ensure that the third CD segment can provide sufficient support at point C, a soldered gold ball is processed at the bonding position between the end of the third CD segment and the top electrode.

[0047] Similarly, in order to improve the support capacity of the first segment AB3 at point B1, a soldered gold ball is processed at the bonding position between the first segment AB3 and the pad.

[0048] Optionally, the fillet angle at the connection point of the first segment AB3 and the second segment B3C is within the range of [80°, 100°]. If the fillet angle is too small, it will lead to instability in the bond wire structure; if the fillet angle is too large, it will lead to a decrease in the bond wire's ability to absorb stress and a reduction in its impact resistance.

[0049] Further, the distance between the chip and the pad is 90 micrometers to 1050 micrometers. Specifically, the distance between the chip and the pad refers to the distance between the edge of the chip facing the pad and the edge of the pad facing the chip; specifically, sufficient space needs to be reserved to form the connection line structure required by the embodiments of the present invention, and at the same time, the risk of line sagging caused by an excessively large span of the connection line needs to be avoided.

[0050] Specifically, the height of the chip in the embodiments of the present invention is greater than 100 micrometers and less than 350 micrometers, and the distance between the chip and the pad is greater than 0.9 times the chip height and less than three times the chip height. Accordingly, it can be calculated that the distance between the chip and the pad is 90 micrometers to 1050 micrometers.

[0051] Further, the value range of the included angle a is 80° < a < 110°, so as to ensure that the lateral component force of the first segment is not too large and ensure the support stability of the first segment.

[0052] Further, the value range of the included angle c is 8° < c < 25°, so as to ensure that the lifting height of the connection line from point D to point C and from point C to point B3 is low, which is beneficial to reducing the height of the encapsulating layer.

[0053] Further, in actual operation, if an LED chip has two top electrodes, considering symmetry and preventing a large difference in the distances from the two top electrodes to the corresponding edges of the LED chip, which leads to an increased risk of line sagging, accordingly, the width of the LED chip is 2 to 2.5 times the distance from the chip electrode to the chip edge, that is, the chip electrode is located in the central area of the top surface of the LED chip.

[0054] Further, the value range of the included angle d between the second segment and the horizontal plane is 8° < d < 25°, which is generally associated with the angle of the included angle c, and the limitation of the angle d can ensure that the final height of B3 is low.

[0055] Figure 2 shows a flow chart of the wire bonding method according to an embodiment of the present invention.

[0056] Accordingly, the present invention also provides a wire bonding method, characterized in that it is used for wire bonding of bonding wires between a top electrode and a corresponding pad in the LED device described above, comprising:

[0057] S101: placing a solder ball on the top surface of the top electrode;

[0058] The top electrode is used as the processing end point of the BSOB process. In order to avoid damage to the top electrode, it is necessary to place a solder ball on the top surface of the top electrode in advance for welding.

[0059] S102: The lead end of the bonding wire is melted into a gold ball through the wire nozzle and bonded to the pad;

[0060] At the start of the BSOB process, the lead end of the bonding wire is melted into a gold ball using a wire nozzle and then bonded to the pad. After the gold ball has solidified, it is connected and fixed to the pad.

[0061] S103: By releasing the wire and moving the bonding wire along a preset trajectory based on the wire nozzle, the first segment AB3, the second segment B3C, and the third segment CD are formed respectively;

[0062] By simultaneously releasing the bonding wire and moving the wire nozzle, the bonding wire moves along a preset trajectory to ultimately form the desired structure of the first segment AB3, the second segment B3C, and the third segment CD.

[0063] S104: The end of the bonding wire is bonded to the solder ball using a wire nozzle and then cut off.

[0064] The end point of the wire tip falls on the solder ball, and the bond wire is cut by melting the bond wire and physically cutting it to form the bond wire.

[0065] The wire bonding method provided in this embodiment of the invention sets the starting point of the BSOB process on the solder pad, which can reduce the arc height.

[0066] In summary, this invention provides an LED device and a wire bonding method. During processing, due to the height difference between the pad and the top electrode, setting the starting point of the BSOB wire bonding process at the pad allows the near-vertical front section of the bond wire to maintain a certain length allowance, avoiding excessive bonding stress between the bond wire and the pad. Correspondingly, reducing the arc height of the bond wire does not significantly affect the bonding stress between the bond wire and the pad, ensuring the stability of the bond wire structure. Setting the ending point of the BSOB wire bonding process on the top electrode allows the solder balls on the top electrode to effectively bond the bond wire at point L. The end segment within the area enclosed by the ED chip outline is well fixed to prevent the connection points of the second and third segments from contacting the LED chip. When the substrate is deformed by heat, due to the presence of the first arch, rounded corners, and second arch, the rounded corners swing away from the center during substrate deformation, and the second arch is subjected to upward stress. The concave shape of the second arch buffers the stress, and the concave shape gradually flattens out. This ensures that the overall height of the bonding wire does not change significantly during the substrate deformation process, thereby preventing the bonding wire from contacting the encapsulation mold and ensuring the smooth molding of the encapsulation colloid and the smooth processing of the LED device.

[0067] The above provides a detailed description of an LED device and wire bonding method provided by the embodiments of the present invention. Specific examples have been used to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of the present invention. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. An LED device, comprising a substrate, an LED chip, a bonding wire and an encapsulant, wherein the substrate is provided with a bonding pad, the LED chip is fixed on the substrate and located at one side of the bonding pad, the LED chip is provided with a top electrode, the top electrode is electrically connected to the bonding pad via the bonding wire, and the LED chip and the bonding wire are encapsulated by the encapsulant; Its features are, The bonding wire comprises a first segment, a second segment and a third segment connected in sequence; The head end of the first segment is bonded to the bonding pad, and an included angle between the first segment and the top surface of the bonding pad away from the LED chip is a; Transition between the first segment and the second segment is achieved via a rounded corner, and an included angle between the first segment and the second segment facing the LED chip is b; The connection position of the second segment and the third segment is located directly above the top edge of the LED chip; The tail end of the third segment is bonded to the top electrode, and an included angle between the third segment and the top surface of the top electrode facing the LED chip is c; The height of the LED chip is h, the height of the highest point of the bonding wire is less than or equal to 1.5h, and the height of the highest point of the bonding wire is greater than h; The height of the connection position of the second segment and the third segment from the top surface of the chip is less than or equal to h / 2, and the height of the connection position of the second segment and the third segment from the top surface of the chip is greater than or equal to h / 6; The middle part of the first segment is provided with a first arch away from the LED chip; The second segment participates in bending the rounded corner at the connection point of the first segment and the second segment, and the acting force generated by the first arch and the rounded corner supports the head end of the second segment at the connection point of the first segment and the second segment; The head end of the third segment is maintained at the connection point of the second segment and the third segment by the fixing acting force of the tail end on the top electrode; The distance between the connection point of the second segment and the third segment and the top surface of the chip is greater than the wire diameter of the bonding wire; The value range of the rounded corner angle at the connection position of the first segment and the second segment is [80°, 100°]; The value range of the included angle a is 80°<a<110°, and the value range of the included angle c is 8°<c<25°; The value range of an included angle d between the second segment and a horizontal plane is 8°<d<25°.

2. The LED device as described in claim 1, characterized in that, The middle part of the second segment is provided with a second arch facing downward.

3. The LED device as described in claim 1, characterized in that, The distance between the chip and the bonding pad is 90 micrometers to 1050 micrometers.

4. The LED device as described in claim 1, characterized in that, The width of the LED chip is 2 to 2.5 times the distance from the chip electrode to the edge of the chip.

5. A wire bonding method, characterized in that, A wire bonding method for bonding wires between a top electrode and a corresponding bonding pad in the LED device according to any one of claims 1 to 4, comprising: planting a solder ball on the top surface of the top electrode; melting the head end of the bonding wire into a gold ball through a capillary and bonding the gold ball onto the bonding pad; driving the bonding wire to move according to a preset track by paying off the wire via the capillary, so as to form the first segment, the second segment and the third segment respectively; bonding the tail end of the bonding wire onto the solder ball through the capillary and then cutting off the bonding wire.

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