阅读说明：本技术 电性贴附结构及其形成方法 (Electrical attachment structure and forming method thereof ) 是由 陈立宜 于 2019-10-23 设计创作，主要内容包括：本发明公开了一种电性贴附结构,其包含基板、接触垫组,以及微型元件以及电极组的组合。接触垫组位于基板之上,其中接触垫组包含至少一个接触垫,并且至少一个接触垫是导电的。组合位于接触垫组之上,电极组的相对两侧分别与微型元件以及接触垫组相接触。接触垫组与电极组间的接触周边在基板上的垂直投影较该微型元件的外周边在基板上的垂直投影长,其中接触周边在基板上的垂直投影被外周边在基板上的垂直投影所包围。此电性贴附结构及其形成方法提供以帮助电极组与接触垫组之间的液体层抓住电极组并将电极组贴附到接触垫组。(The invention discloses an electrical property attaching structure, which comprises a substrate, a contact pad group, a micro element and an electrode group combination. The contact pad set is located on the substrate, wherein the contact pad set comprises at least one contact pad, and the at least one contact pad is conductive. The assembly is located on the contact pad set, and two opposite sides of the electrode set are respectively contacted with the micro-device and the contact pad set. The perpendicular projection of the contact periphery of the contact pad group and the electrode group on the substrate is longer than that of the outer periphery of the micro-component on the substrate, wherein the perpendicular projection of the contact periphery on the substrate is surrounded by the perpendicular projection of the outer periphery on the substrate. The electrical attachment structure and the method of forming the same provide for assisting the liquid layer between the electrode assembly and the contact pad assembly to grip the electrode assembly and attach the electrode assembly to the contact pad assembly.)

1. An electrical attachment structure, comprising:

a substrate;

a set of contact pads located over the substrate, wherein the set of contact pads comprises at least one contact pad, wherein the contact pad is electrically conductive; and

the combination of a micro-component and an electrode set is located on the contact pad set, the electrode set comprises at least one electrode, two opposite sides of the electrode set are respectively in contact with the micro-component and the contact pad set, a perpendicular projection of a contact periphery between the contact pad set and the electrode set on the substrate is longer than a perpendicular projection of an outer periphery of the micro-component on the substrate, and the perpendicular projection of the contact periphery on the substrate is surrounded by the perpendicular projection of the outer periphery on the substrate.

2. The electrical attachment structure of claim 1 further comprising: and the adhesion layer is arranged between the contact pad group and the substrate.

3. The electrical connection structure of claim 1, wherein one of the set of contact pads and the set of electrodes comprises one of copper, tin, titanium, and indium.

4. The electrical attachment structure of claim 1 wherein the lateral length of the micro-device is less than or equal to 100 microns.

5. A method of forming an electrical attachment structure, comprising:

forming a set of contact pads on a substrate, wherein the set of contact pads includes at least one contact pad, and the at least one contact pad is electrically conductive;

placing a combination of a micro-component and an electrode set on the contact pad set such that opposite sides of the electrode set are in contact with the micro-component and the contact pad set, respectively, the electrode set comprising at least one electrode, a perpendicular projection of a contact perimeter between the contact pad set and the electrode set on the substrate being longer than a perpendicular projection of an outer perimeter of the micro-component on the substrate, and the perpendicular projection of the contact perimeter on the substrate being surrounded by the perpendicular projection of the outer perimeter of the micro-component on the substrate;

forming a liquid layer between the set of electrodes and the set of contact pads such that the microelements are captured by capillary forces generated by the liquid layer; and

evaporating the liquid layer such that the electrode assembly is attached to and electrically connected with the contact pad set.

6. The method of claim 5, wherein forming the liquid layer comprises:

reducing the temperature of the set of contact pads in an environment containing vapor to condense at least a portion of the vapor to form the liquid layer.

7. The method of claim 5, wherein forming the liquid layer comprises:

spraying a vapor on the substrate such that at least a portion of the vapor condenses to form the liquid layer.

8. The method of claim 7, wherein the vapor has a water vapor pressure higher than ambient water vapor pressure.

9. The method of claim 7, wherein the vapor comprises nitrogen and water.

10. The method of claim 5, further comprising forming an adhesive layer on the substrate prior to forming the set of contact pads.

11. The method of claim 5, wherein the liquid layer comprises water.

12. The method of claim 6, wherein said liquid layer is formed at a dew point temperature.

13. The method of claim 5, wherein evaporating the liquid layer comprises:

after the liquid layer is evaporated, the temperature of the contact pad set is raised so that the electrode set is adhesively fixed to the contact pad set.

14. The method of claim 5, wherein at least one of the set of contact pads and the set of electrodes comprises an adhesive material, and further comprising:

after evaporating the liquid layer, raising the temperature of the set of contact pads above the melting point of the bonding material.

15. The method of claim 5, wherein at least one of the set of contact pads and the set of electrodes comprises an adhesive material, and further comprising:

after evaporating the liquid layer, raising the temperature of the set of contact pads to below the melting point of the bonding material and above the boiling point of the liquid layer.

16. The method of claim 5, further comprising:

after evaporating the liquid layer, raising the temperature of the set of contact pads above the eutectic point of the set of contact pads and the set of electrodes.

17. The method of claim 5, wherein the thickness of the liquid layer between the set of electrodes and the set of contact pads is less than the thickness of the microelements when the microelements are gripped by the capillary force.

18. The method of claim 5, wherein one of the set of contact pads and the set of electrodes comprises one of copper, tin, titanium, and indium.

19. The method of claim 5, wherein the microelements have a lateral length of less than or equal to 100 microns.

Technical Field

The present invention relates to an electrical attachment structure, and more particularly, to an electrical attachment structure and a method for forming the same.

Background

Conventional techniques for transferring components include transferring from a transfer chip to a receiving substrate by die bonding. One such embodiment is "direct bonding", which involves one bonding step from the transfer chip to the array of elements of the receiving substrate, followed by removal of the transfer chip. Another such embodiment is "indirect bonding", which involves two bonding/peeling steps. In indirect bonding, the transfer head may pick up an array of elements from a donor substrate, bond the array of elements to a receiving substrate, and then remove the transfer head.

One of the important issues that may affect the transfer quality is the moment the component is in contact with the receiving chip.

Disclosure of Invention

The present invention is directed to overcoming the drawbacks of the prior art and providing an electrical attachment structure and a method for forming the same, which enables a micro device to be better held in place for subsequent bonding.

According to some embodiments of the present invention, an electrical attachment structure is provided. The electrical property attaching structure comprises a substrate, a contact pad group, and a combination of a micro element and an electrode group. The contact pad set is located on the substrate, wherein the contact pad set comprises at least one contact pad, and at least one contact pad is conductive. The combination of the micro-element and the electrode group is positioned on the contact pad group, the electrode group comprises at least one electrode, and two opposite sides of the electrode group are respectively contacted with the micro-element and the contact pad group. The perpendicular projection of the contact periphery of the contact pad group and the electrode group on the substrate is longer than the perpendicular projection of the outer periphery of the micro-component on the substrate, wherein the perpendicular projection of the contact periphery on the substrate is surrounded by the perpendicular projection of the outer periphery on the substrate.

According to an embodiment of the present invention, the electrical attachment structure further includes an adhesive layer between the contact pad set and the substrate.

According to an embodiment of the present invention, one of the contact pad set and the electrode set includes one of copper, tin, titanium, and indium.

According to an embodiment of the present invention, the lateral length of the micro-device is less than or equal to 100 μm.

According to some embodiments of the present invention, a method of forming an electrical attachment structure is provided. The method comprises the following steps: forming a set of contact pads on a substrate, wherein the set of contact pads includes at least one contact pad, and the at least one contact pad is electrically conductive; placing a combination of a micro-component and an electrode group on the contact pad group, so that two opposite sides of the electrode group are respectively contacted with the micro-component and the contact pad group, wherein the electrode group comprises at least one electrode, the vertical projection of the contact periphery between the contact pad group and the electrode group on the substrate is longer than that of the outer periphery of the micro-component on the substrate, and the vertical projection of the contact periphery on the substrate is surrounded by that of the outer periphery of the micro-component on the substrate; forming a liquid layer between the electrode assembly and the contact pad assembly such that the micro-device is captured by capillary forces generated by the liquid layer; and evaporating the liquid layer so that the electrode group is attached to the contact pad group and electrically connected with the contact pad group.

According to an embodiment of the present invention, forming a liquid layer comprises: the temperature of the set of contact pads is reduced in an environment containing vapor to condense at least a portion of the vapor to form a liquid layer.

According to an embodiment of the present invention, forming a liquid layer comprises: a vapor is sprayed on the substrate such that at least a portion of the vapor condenses to form a liquid layer.

According to one embodiment of the present invention, the water vapor pressure of the vapor is higher than the ambient water vapor pressure.

According to an embodiment of the invention, the vapor comprises nitrogen and water.

According to an embodiment of the invention, an adhesive layer is formed on the substrate before the contact pad set is formed.

According to an embodiment of the invention, the liquid layer comprises water.

According to an embodiment of the invention, the liquid layer is formed at a temperature of the dew point.

According to one embodiment of the present invention, the evaporated liquid layer comprises: after the liquid layer is evaporated, the temperature of the contact pad set is raised so that the electrode set is adhesively secured to the contact pad set.

According to an embodiment of the present invention, at least one of the set of contact pads and the set of electrodes comprises a bonding material, and after evaporating the liquid layer, the temperature of the set of contact pads is raised to above the melting point of the bonding material.

According to an embodiment of the present invention, at least one of the set of contact pads and the set of electrodes comprises a bonding material, and after evaporating the liquid layer, the temperature of the set of contact pads is raised to below the melting point of the bonding material and above the boiling point of the liquid layer.

According to an embodiment of the invention, after evaporating the liquid layer, the temperature of the set of contact pads is raised above the eutectic point of the set of contact pads and the set of electrodes.

According to one embodiment of the present invention, the thickness of the liquid layer between the electrode set and the contact pad set is less than the thickness of the micro-device when the micro-device is held by capillary force.

According to an embodiment of the present invention, one of the contact pad set and the electrode set includes one of copper, tin, titanium, and indium.

According to an embodiment of the present invention, the lateral length of the micro-device is less than or equal to 100 μm.

Compared with the prior art, the invention has obvious advantages and beneficial effects. By means of the technical scheme, the electric attaching structure and the forming method thereof help the liquid layer between the electrode group and the contact pad group to grasp the electrode group and attach the electrode group to the contact pad group. The electrical attachment structure is just capable of making the contact perimeter larger than the original contact perimeter to enhance the capillary force generated by the liquid layer for grasping the electrodes.

The foregoing is merely illustrative of the problems to be solved, solutions to problems, and effects produced by the present invention, and the details of which are set forth in the following description and related drawings.

Drawings

In order to make the aforementioned and other objects, features, advantages and embodiments of the invention more comprehensible, the following description is given:

FIG. 1 is a schematic cross-sectional view of an electrical attachment structure according to some embodiments of the present invention;

FIG. 1B is a perspective view of an electrical attachment structure according to some embodiments of the present invention;

FIG. 1C is a schematic bottom view of the top contact surface of a contact pad set according to some embodiments of the invention;

FIG. 1D is a schematic bottom view of the bottom contact surface of an electrode assembly according to some embodiments of the inventions;

FIG. 1E is a schematic bottom view of a set of contact pads and an electrode set when the electrode set is close to or in contact with the set of contact pads, according to some embodiments of the invention;

FIG. 1F is a schematic view of a contact perimeter according to some embodiments of the present invention;

FIG. 1G is a schematic view of an original contact perimeter in accordance with some embodiments of the present invention;

FIG. 1H is a schematic perspective view of a liquid layer in contact with an electrode set and a contact pad set according to some embodiments of the present invention;

FIG. 2 is a schematic bottom view of a set of contact pads and an electrode set when the electrode set is close to or in contact with the set of contact pads according to some embodiments of the invention;

FIG. 3A is a schematic bottom view of a set of contact pads and an electrode set when the electrode set is close to or in contact with the set of contact pads according to some embodiments of the invention;

FIG. 3B is a schematic bottom view of a set of contact pads and an electrode set when the electrode set is close to or in contact with the set of contact pads according to some embodiments of the invention;

FIG. 4 is a schematic top view of a set of contact pads and an electrode set when the electrode set is near or in contact with the set of contact pads according to some embodiments of the invention;

FIG. 5A is a schematic cross-sectional view of one type of contact pad set and electrode set in accordance with some embodiments of the invention;

FIG. 5B is a schematic cross-sectional view of one type of contact pad set and electrode set in accordance with some embodiments of the invention;

FIG. 5C is a schematic cross-sectional view of one type of contact pad set and electrode set in accordance with some embodiments of the invention;

FIG. 6A is a schematic cross-sectional view of an electrical attachment structure according to some embodiments of the present invention;

FIG. 6B is a schematic bottom view of the contact pad set and the electrode set when the electrode set is close to or in contact with the contact pad set according to some embodiments of the invention;

FIG. 7 is a schematic bottom view of a set of contact pads and an electrode set when the electrode set is near or in contact with the set of contact pads according to some embodiments of the invention;

FIG. 8 is a flow chart of a method of forming an electrical attachment structure according to some embodiments of the present invention;

FIG. 9A is a cross-sectional view of an intermediate stage of a method of forming an electrical attachment structure according to some embodiments of the present invention;

FIG. 9B is a cross-sectional view of an intermediate stage of a method of forming an electrical attachment structure according to some embodiments of the present invention;

FIG. 9C is a cross-sectional view of an intermediate stage of a method of forming an electrical attachment structure according to some embodiments of the present invention; and

FIG. 9D is a cross-sectional view of an intermediate stage of a method of forming an electrical attachment structure according to some embodiments of the present invention.

[ description of main symbols ]

100A, 100E: electrical property attaching structure

110: substrate

120A、120A’、120A”、120A”’、120B、120C、120D、120D’、120E、

120F: contact pad set

120A-1, 120A' -1: contact pad

120A-tcs: top contact surface

130A、130A’、130A”、130A”’、130B、130C、130D、130D’、130E、

130F: electrode group

130A-1, 130A' -1: electrode for electrochemical cell

130A-bcs: bottom contact surface

140: micro-element

150: liquid layer

152: meniscus of liquid

200: method of producing a composite material

L: lateral length

OP: outer periphery of

CP, CP1, CP2, CP3, CP 4: contact perimeter

PCP (primary phenol treatment): original contact periphery

SP: concave part

T: thickness of

HP: hollow part

210-240: operation of

Detailed Description

While the spirit of the invention will be described in detail and with reference to the drawings, those skilled in the art will understand that various changes and modifications can be made without departing from the spirit and scope of the invention as taught herein.

In various embodiments, reference is made to the accompanying drawings. However, certain embodiments may be practiced without one or more of these specific details, or in combination with other known methods and configurations. In the following description, for purposes of explanation, numerous implementation details, such as implementation configurations, dimensions, and processes, are set forth in order to provide a thorough understanding of the embodiments described herein. In other instances, well-known and conventional semiconductor processing and fabrication techniques have not been described in particular detail in order to not unnecessarily obscure the present invention. Reference throughout this specification to "one embodiment," "an embodiment," etc., means that a particular feature, structure, configuration, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, the appearances of the phrases "in one embodiment," "in an embodiment," and the like, in various places throughout this specification are not necessarily all referring to the same embodiment of the invention. Furthermore, the particular features, structures, configurations, or characteristics may be combined in any suitable manner in one or more embodiments.

The terms "above," "to," "over," "in," "between," and "over" as used herein may refer to the relative position of one layer with respect to another layer. One layer "on" or "over" or bonded to another layer, may be directly in contact with the other layer, or may have one or more intervening layers. One layer "between" layers may be directly in contact with the layers, or may have one or more intervening layers.

Referring to fig. 1A to 1E, fig. 1A is a cross-sectional view of an electrical attachment structure 100A according to some embodiments of the invention, fig. 1B is a perspective view of the electrical attachment structure 100A according to some embodiments of the invention, and fig. 1B provides a three-dimensional view, which makes the structural features of the electrical attachment structure 100A easier to understand. FIG. 1C is a schematic bottom view of the top contact surfaces 120A-tcs of the contact pad set 120A according to some embodiments of the invention, FIG. 1D is a schematic bottom view of the bottom contact surfaces 130A-bcs of the electrode set 130A according to some embodiments of the invention, and FIG. 1E is a schematic bottom view of the contact pad set 120A when the electrode set 130A is near or in contact with the contact pad set 120A according to some embodiments of the invention. Note that no reference numeral for the electrode group 130A is present in fig. 1E, because the electrode group 130A coincides with (or completely overlaps) the contact pad group 120A in the bottom view. The electrical attachment structure 100A includes a substrate 110, a set of contact pads 120A, and a combination of a micro-device 140 and an electrode set 130A. The contact pad set 120A is located on the substrate 110, wherein the contact pad set 120A includes at least one contact pad 120A-1, and the contact pad 120A-1 is electrically conductive. In some embodiments, the thickness of the set of contact pads 120A is less than or equal to about 2 micrometers (μm), and preferably less than or equal to about 0.5 micrometers. The combination of the microelements 140 and the electrode assembly 130A is located on the contact pad assembly 120A, and the electrode assembly 130A comprises at least one electrode 130A-1. In some embodiments, the electrode set 130A has a thickness in the range of about 0.2 microns to about 2 microns, and preferably in the range of about 0.3 microns to about 1 micron. The electrode assembly 130A is in contact with the microelements 140 and the contact pad assembly 120A on opposite sides thereof. The perpendicular projection of the contact perimeter CP (of the contact area) between the set of contact pads 120A and the set of electrodes 130A on the substrate 110 is longer than the perpendicular projection of the outer perimeter OP of the microelements 140 on the substrate 110. The perpendicular projection of the contact perimeter CP on the substrate 110 is surrounded by the perpendicular projection of the outer perimeter OP of the microelements 140 on the substrate 110.

Fig. 1F is a schematic diagram of the contact periphery CP according to some embodiments of the invention, fig. 1G is a schematic diagram of the original contact periphery PCP according to some embodiments of the invention, and fig. 1H is a perspective schematic diagram of the liquid layer 150 respectively contacting the electrode assembly 130A and the contact pad assembly 120A according to some embodiments of the invention. In some embodiments, due to the intentionally designed shape of the contact pad set 120A (e.g., the shape of "H" as illustrated in fig. 1C) and the electrode set 130A (e.g., the shape of "H" as illustrated in fig. 1D), when the contact pad set 120A and the electrode set 130A are close to the liquid layer 150 (e.g., the water layer) therebetween and opposite sides of the liquid layer 150 respectively contact the contact pad set 120A and the electrode set 130A, the total length of the contact perimeter CP (as illustrated in fig. 1F) is greater than the total length of the original contact perimeter PCP, wherein the shapes of the contact pad set 120A and the electrode set 130A are not intentionally designed (as illustrated in fig. 1G). FIG. 1F may also be useful in understanding the described embodiments. These intentionally designed shapes are designed to increase the total length of the contact perimeter CP between the contact pad set 120A and the electrode set 130A. Taking the embodiment shown in fig. 1C and 1D as an example, when the shapes of the contact pad set 120A and the electrode set 130A are "H", the contact periphery CP is larger than the original contact periphery PCP, wherein the shapes of both the contact pad set 120A and the electrode set 130A are square. Note that this comparison is made under the assumption that if the recessed portion SP of "H" (as shown in fig. 1F) is refilled, in which case the total area thereof will be the same as that of the square shown in fig. 1G.

Perspective (three-dimensional view) views illustrating the above embodiment are shown in fig. 1B and 1H. In some embodiments, the electrode set 130A and the contact pad set 120A may be brought into proximity with each other and into contact with the liquid layer 150 therebetween such that the combination of the electrode set 130A and the microelements 140 thereon is captured by capillary forces generated by the liquid layer 150 (see, e.g., figure 1H, where a meniscus 152 of the liquid layer 150 is formed due to the capillary forces). Then, the liquid layer 150 is evaporated to adhere the electrode assembly 130A to the contact pad assembly 120A. In these embodiments, since the contact pad set 120A and the electrode set 130A are designed as "H", the capillary force is larger than that when the electrode set 130A and the contact pad set 120A are designed as a square. This greater capillary force greatly aids in the quality of the attachment and subsequent adhesion between the electrode assembly 130A and the contact pad assembly 120A, since the capillary force helps to secure the electrode assembly 130A in the controlled area when the electrode assembly 130A is adhered to the liquid layer 150. Further, this capillary force may help form an attachment (and also an adhesion) between the electrode assembly 130A and the contact pad assembly 120A during and after evaporation of the liquid layer 150. This attachment is a particular phenomenon found in these kinds of liquid layers 150 that helps to grip and contact. This adhesion is a phenomenon that occurs when two objects (usually metals) are in contact and atoms diffuse between the two objects. In some embodiments, the microelements 140 have a lateral length L that is less than or equal to about 100 microns, which is limited to ensure that capillary forces significantly aid and govern the attachment between the set of electrodes 130A and the set of contact pads 120A.

It is noted that the contact perimeter CP and the original contact perimeter PCP can be interpreted as a single contact perimeter (or a plurality of separate contact perimeters, as will be mentioned later in some embodiments) when the electrode set 130A is in contact with the contact pad set 120A. When the liquid layer 150 is interposed between and in contact with the electrode set 130A and the contact pad set 120A, they may also be interpreted as a single contact perimeter (or multiple contact perimeters). In this case, the contact perimeter CP (and the original contact perimeter PCP) is considered to have a perimeter with a thickness T (as shown in FIG. 1H) measured from the bottom contact surfaces 130A-bcs of the electrode set 130A through the perimeter of the liquid layer 150 to the top contact surfaces 120A-tcs of the contact pad set 120A.

Referring to fig. 2-3B, fig. 2 is a schematic bottom view of the contact pad set 120A ' and the electrode set 130A ' (not explicitly shown, since it overlaps and is behind the contact pad set 120A ' in fig. 2) when the electrode set 130A ' is close to or in contact with the contact pad set 120A ' according to some embodiments of the invention. Fig. 3A is a schematic bottom view of the contact pad set 120A "and the electrode set 130A" (not explicitly shown because it overlaps and is behind the contact pad set 120A "in fig. 3A) when the electrode set 130A" is near or in contact with the contact pad set 120A "in accordance with some embodiments of the invention. Fig. 3B is a schematic bottom view of the contact pad set 120A ' "and the electrode set 130A '" (not explicitly shown because it overlaps and is behind the contact pad set 120A ' "in fig. 3B) when the electrode set 130A '" is near or in contact with the contact pad set 120A ' ", according to some embodiments of the invention. The contact pad set 120A ' "includes a plurality of contact pads 120A '" -1 and the electrode set 130A ' "includes a plurality of electrodes 130A '" -1 (not explicitly shown as they overlap and are located behind the contact pads 120A ' "-1 in fig. 3B). Note that the electrode sets 130A ', 130A ", 130A'" are not labeled in fig. 2-3B because the electrode sets 130A ', 130A ", 130A'" are respectively coincident with (or completely overlap with) the contact pad sets 120A ', 120A ", 120A'" in bottom view. Note that fig. 1A can also be explained by fig. 2, since fig. 1A is a sectional view. In the embodiment shown in fig. 2, the contact pad set 120A 'and the electrode set 130A' are hollowed out such that the contact perimeter CP is composed of a first contact perimeter CP1 and a second contact perimeter CP2 that are separated from each other (i.e., CP1+ CP 2). In various embodiments of the present invention, all contact perimeters are labeled "CP" for simplicity, even if there are different shapes of contact perimeters. The technical effect of the embodiment shown in fig. 2 is similar to that of the embodiments shown in fig. 1C to 1E and will not be described in detail.

The embodiment shown in fig. 3A may be considered a modification of the embodiment shown in fig. 2. The contact pad set 120A "and the electrode set 130A" of the embodiment shown in fig. 3A have a plurality of separated hollow portions HP. In the embodiment shown in fig. 3B, the plurality of contact pads 120A '"-1 and the plurality of electrodes 130A'" -1 (again, not explicitly shown due to "overlap") form a plurality of contact perimeters CP1, CP2, CP3, etc., the contact perimeter CP being a sum of the plurality of contact perimeters CP1, CP2, CP3, etc. Note that one of the contact pads 120A' "-1 is connected to the outside and is electrically connected to a voltage source (not shown).

Fig. 4 is a schematic bottom view of the contact pad set 120B and the electrode set 130B when the electrode set 130B is close to or in contact with the contact pad set 120B according to some embodiments of the invention. In these embodiments, the microelement 140 has a dimension (or lateral length L) that is smaller than the set of contact pads 120B.

Referring to fig. 5A to 5C, fig. 5A to 5C are schematic cross-sectional views of three different types of contact pad sets and electrode sets according to some embodiments of the invention. In these embodiments, the perpendicular projection of the at least one contact perimeter CP on the substrate 110 is spanned by the perpendicular projection of the set of contact pads 120C, 120D 'on the substrate 110 and/or the perpendicular projection of the set of electrodes 130C, 130D' on the substrate 110.

Referring to fig. 6A, 6B, and 7, fig. 6A is a cross-sectional view of an electrical attachment structure 100E according to some embodiments of the invention, fig. 6B is a bottom view of a contact pad set 120E and an electrode set 130E (again, not explicitly shown due to "coincidence") when an electrode set 130E is close to or in contact with the contact pad set 120E according to some embodiments of the invention, and fig. 7 is a bottom view of a contact pad set 120F and an electrode set 130F (again, not explicitly shown due to "coincidence") according to some embodiments of the invention when an electrode set 130F is close to or in contact with the contact pad set 120F. Fig. 6A and 6B illustrate an embodiment in which the set of contact pads 120E and the set of electrodes 130E have a zig-zag shape (or similar thereto), while fig. 7 illustrates an embodiment in which the set of contact pads 120F and the set of electrodes 130F have a spiral shape. The above embodiments show some other possible structural features that comply with all the constraints as described above and that are also capable of increasing the capillary force.

Fig. 8 is a flowchart of a method 200 of forming an electrical attachment structure 100A according to some embodiments of the present invention, and fig. 9A-9D are cross-sectional views of intermediate stages of the method 200 of fig. 8 according to some embodiments of the present invention. Referring to fig. 8 to 9D, the method 200 begins with operation 210, in which a contact pad set 120A is formed on the substrate 110, and the contact pad set 120A includes at least one contact pad 120A-1, and the contact pad 120A-1 is conductive (see fig. 9A). In some embodiments, an adhesive layer (not shown) is formed on the substrate 110 before the contact pad set 120A is formed. The method 200 continues with operation 220 in which the combination of the micro-device 140 and the electrode assembly 130A is placed on the contact pad assembly 120A such that opposite sides of the electrode assembly 130A are in contact with the micro-device 140 and the contact pad assembly 120A, respectively, the electrode assembly 130A including at least one electrode 130A-1. The perpendicular projection of the contact perimeter CP between the contact pad group 120A and the electrode group 130A on the substrate 110 is longer than the perpendicular projection of the outer perimeter OP of the micro-device 140 on the substrate 110, and the perpendicular projection of the contact perimeter CP on the substrate 110 is surrounded by the perpendicular projection of the outer perimeter OP of the micro-device 140 on the substrate 110 (see fig. 9B).

The method 200 continues with operation 230 in which a liquid layer 150 is formed between the electrode assembly 130A and the contact pad assembly 120A such that the micro-devices 140 are captured by the capillary force generated by the liquid layer 150 (see figure 9C). In some embodiments, liquid layer 150 comprises water. It is noted that operation 220 and operation 230 may be interchanged. In some other embodiments, the liquid layer 150 is formed on the set of contact pads 120A, and then the combination of the electrode assembly 130A and the micro-devices 140 is placed on the set of contact pads 120A such that the electrode assembly 130A contacts the liquid layer 150 and is captured by the capillary force generated by the liquid layer 150. In some embodiments, the liquid layer 150 may be formed by reducing the temperature of the contact pad set 120A in an environment containing vapor, causing at least a portion of the vapor to condense to form the liquid layer 150. In some embodiments, the liquid layer 150 is formed at a temperature of about the dew point. In some embodiments, the liquid layer 150 may be formed by spraying vapor on the substrate 110 such that at least a portion of the vapor condenses to form the liquid layer 150. In some embodiments, the vapor pressure of the vapor is higher than the ambient vapor pressure, the vapor consisting essentially of nitrogen and water. In some embodiments, the thickness of the liquid layer 150 between the electrode assembly 130A and the contact pad assembly 120A is less than the thickness of the microelements 140 when the microelements 140 are gripped by the capillary force generated by the liquid layer 150.

The method 200 continues with operation 240 in which the liquid layer 150 is evaporated such that the electrode assembly 130A is adhesively secured and attached to the contact pad set 120A and electrically connected to the contact pad set 120A (see fig. 9 d. in some embodiments, the liquid layer 150 is evaporated by raising the temperature of the contact pad set 120A. in some embodiments, one of the contact pad set 120A and the electrode assembly 130A includes a bonding material, and the temperature of the contact pad set 120A may be further raised to a point to bond the electrode assembly 130A to the contact pad set 120A. the point may be above the melting point of the bonding material, below the melting point of the bonding material and above the boiling point of the liquid layer 150, or above the eutectic point of the contact pad set 120A and the electrode assembly 130A. in some embodiments, the bonding material has a thickness in a range from about 0.2 microns to about 2 microns, and in some embodiments, the bonding material has a preferred thickness in a range from about 0.3 microns to about 1 micron One of a may comprise one of copper (copper) and a copper-rich material. The bonding material may be tin (tin) -rich material, indium (indium) -rich material, or titanium (titanium) -rich material. Here, "rich" means more than half of the total number of atoms.

In summary, an electrical attachment structure and a method for forming the same are provided to help a liquid layer between an electrode assembly and a contact pad assembly to hold the electrode assembly and attach the electrode assembly to the contact pad assembly. The electrical attachment structure, as described in the specification, allows the contact perimeter to be larger than the original contact perimeter to enhance the capillary force generated by the liquid layer for grasping the electrodes.

Although the present invention has been described with reference to the above embodiments, it should be understood that various changes and modifications may be made therein by those skilled in the art without departing from the spirit and scope of the invention as defined in the appended claims.