CN113905539A

CN113905539A - LED chip printing steel mesh

Info

Publication number: CN113905539A
Application number: CN202111138518.8A
Authority: CN
Inventors: 王东山; 王思博; 廖汉忠
Original assignee: Huaian Aucksun Optoelectronics Technology Co Ltd
Current assignee: Huaian Aucksun Optoelectronics Technology Co Ltd
Priority date: 2021-09-27
Filing date: 2021-09-27
Publication date: 2022-01-07
Anticipated expiration: 2041-09-27
Also published as: CN113905539B

Abstract

The invention relates to the field of semiconductors, and discloses an LED chip printing steel mesh which comprises a steel plate (1) and a plurality of pad openings (2) formed in the steel plate (101), wherein the shape of each pad opening (2) is the same as that of each tin ball pad (3) on an LED chip to be printed, and the LED chip printing steel mesh is characterized in that the area of each pad opening (2) is larger than that of each tin ball pad (3), and compared with the condition that the area of each pad opening (2) is equal to that of each tin ball pad (3), the thickness of the printing steel mesh, namely the thickness of each pad opening (2), is reduced, and the volume of a tin ball positioned on each tin ball pad (3) is kept unchanged after printing and reflowing. Compared with the prior art, the printing steel mesh has low precision requirement during printing, is easy to demould, reduces the abnormal rate of solder paste tip pulling generated by printing, and improves the uniformity of high-density printing.

Description

LED chip printing steel mesh

Technical Field

The invention relates to the field of semiconductors, in particular to an LED chip printing steel mesh.

Background

At present, high-density LED chips are densely distributed on a chip source, the printing precision of a steel mesh is high, and the size of a pad opening on an LED chip printing steel mesh in the prior art is smaller than or equal to that of a pad on an LED chip to be printed. The requirement is that the precision of the opening of the bonding pad is high when the steel mesh is manufactured, otherwise, the offset of the steel mesh is large, so that alignment difference is easily generated between the bonding pad and the bonding pad on the LED chip to be printed during subsequent printing, so that the printing uniformity of high-density solder paste is poor, and due to the small size of the opening of the bonding pad, printing abnormalities such as solder paste tip pulling and the like are easily generated during demolding after the solder paste is printed, and in addition, the thickness of the steel mesh, namely the thickness of the opening of the bonding pad, is thick, so that the demolding difficulty is caused.

Disclosure of Invention

The purpose of the invention is as follows: aiming at the problems in the prior art, the invention provides the LED chip printing steel mesh, which has the advantages that the requirement on the precision of the printing steel mesh is reduced during printing, the demoulding is easy, the abnormal rate of solder paste tip pulling generated by printing is reduced, and the uniformity of high-density printing is improved.

The technical scheme is as follows: the invention provides an LED chip printing steel mesh which comprises a steel plate and a plurality of pad openings arranged on the steel plate, wherein the shape of each pad opening is the same as that of each tin ball pad on an LED chip to be printed.

Preferably, the area of each pad opening is larger than the area of each tin ball pad by: and expanding the pad opening by 10-50um outwards by taking the solder ball pad as a center. The shape of pad opening and tin ball pad is the same completely, enlarges the area of pad opening through the mode that uses tin ball pad as the center outwards enlargies for when the printing steel net is arranged in and is waited to print on the LED chip, the position of pad opening and tin ball pad belongs to concentric position, arranges in when printing, and the relative tin ball pad of tin cream on the tin ball pad that is located in the pad opening can not squint, makes the printing homogeneity good.

Preferably, the area of each pad opening is defined to be the same as the area of each tin ball pad, the thickness of each pad opening is T1, the area of each pad opening is S1, and the volume of the tin ball on the tin ball pad after printing and reflowing is V = S1 · T1; when the area of each pad opening is defined to be larger than the area of each tin ball pad, the thickness of the pad opening is T2, the area of the pad opening is S2, the volume of the tin ball on the tin ball pad after printing and reflowing is V = S2. T2, and the thickness of the pad opening is T2= T1 (1-S1/S2) after the area of the pad opening is increased to S2. That is, under the unchangeable condition of the volume of the tin ball that lies in on the tin ball pad after keeping the printing backward flow in this application, through reducing the open-ended thickness of pad with the increase of the open-ended area of pad, thinner open-ended thickness of pad, the thickness of thinner steel mesh promptly can make the drawing of patterns easy, is difficult for producing during the drawing of patterns that printing such as tin cream draws the point unusual.

Preferably, if the shape of the solder ball pad is rectangular, and the height of the solder ball on the solder ball pad after printing and reflow is defined as h, the loss ratio of the solder paste during demolding after printing is R, the ratio of the length L1 of the pad opening to the length L2 of the solder ball pad is a, and the ratio of the width W1 of the pad opening to the width W2 of the solder ball pad is b, T2= h/(a · b · R).

Preferably, L1-L2= W1-W2=10-50 um. That is, if the solder ball pad is rectangular, the pad opening on the printing steel net in the present application is also rectangular, and the length and width of the pad opening are 10-50um larger than those of the solder ball pad, respectively.

Preferably, the ratio a =1.05-1.2 of the length L1 of the pad opening to the length L2 of the solder ball pad; the ratio b =1.03-1.2 of the width W1 of the pad opening to the width W2 of the solder ball pad.

Preferably, the number of the pad openings on the steel plate is an even number greater than or equal to 2. The number of the solder ball pads on the LED chip is designed mainly because the leveling design of the LED chip is considered to be an even number, if the number of the solder ball pads is an odd number, the phenomenon of crystal falling caused by horizontal failure can occur in use, and the number of the pad openings on the printing steel mesh is determined by the number of the solder ball pads on the LED chip.

Preferably, the printing steel mesh is made of a Ni material.

Has the advantages that: the application provides a modified LED chip printing steel mesh, under the unchangeable condition of volume of the tin ball that lies in on the tin ball pad after keeping the printing backward flow, reduce the thickness of printing steel mesh (being pad open-ended thickness) through increasing the open-ended area of pad on the printing steel mesh, and pad open-ended width/pad open-ended thickness that equals to pad open-ended width/pad, pad open-ended thickness reduces, the width increases, then pad open-ended width/thickness ratio increases, and then relative offset when can reducing the printing, the printing steel mesh after the attenuate can make the drawing of patterns better easy, the tin cream that produces when reducing the demoulding draws printing abnormalities such as point, improve the holistic homogeneity of film source.

Drawings

FIG. 1 is a schematic diagram of a structure of a two-electrode LED chip (left) and a corresponding structure of a two-electrode printing steel mesh (right);

FIG. 2 is a schematic diagram of a structure of a four-electrode LED chip (left) and a corresponding structure of a four-electrode printing steel mesh (right);

FIG. 3 is a schematic diagram of a structure of a six-electrode LED chip (left) and a structure of a corresponding six-electrode printing steel mesh (right);

fig. 4 is a schematic perspective view of a single pad opening in a printing steel mesh for an LED chip.

Detailed Description

The present invention will be described in detail with reference to the accompanying drawings.

The embodiment provides an LED chip printing steel mesh, as shown in figures 1 to 4, which comprises a steel plate 1 and 2 (as shown in figure 1), 4 (as shown in figure 2) or 6 (as shown in figure 3) rectangular pad openings 2 arranged on the steel plate 1, wherein the shape of each pad opening 2 is the same as that of each solder ball pad 3 on an LED chip to be printed, the area of each pad opening 2 is larger than that of each solder ball pad 3, and the LED chip printing steel mesh is realized by outwards expanding the pad openings 2 by 10-50um by taking the solder ball pads 3 as centers. After the area of the pad opening 2 is increased, the thickness of the printing steel net, that is, the thickness of the pad opening 2 is reduced, compared to when the area of the pad opening 2 is equal to the area of each of the solder ball pads 3, and the volume of the solder ball on each of the solder ball pads 3 after the printing reflow is maintained.

In order to more clearly explain the technical scheme, the area of each pad opening 2 is defined to be the same as that of each ball pad 3, the thickness of each pad opening 2 is defined as T1, the area of each pad opening 2 is defined as S1, and the volume of the ball positioned on the ball pad 3 after printing and reflowing is defined as V = S1. T1; when the area of each pad opening 2 is defined to be larger than the area of each ball pad 3, the thickness of the pad opening 2 is T2, the area of the pad opening 2 is S2, and the volume of the ball on the ball pad 3 after printing and reflowing is V = S2 · T2, then the thickness T2= T1 of the pad opening 2 can be obtained from S1 · T1= S2 · T2 after the area of the pad opening 2 is increased to S2 (1-S1/S2).

When the height of the solder ball on the solder ball pad 3 after the printing reflow is defined as h, the loss ratio of the solder paste during demolding after the printing is defined as R, the ratio of the length L1 of the pad opening 2 to the length L2 of the solder ball pad 3 is defined as a, and the ratio of the width W1 of the pad opening 2 to the width W2 of the solder ball pad 3 is defined as b, the thickness of the pad opening 2 is defined as T2= h/(a · b · R) when h = (L1 · W1 · T2 · R)/(L2 · W2) indicates that the area of the pad opening 2 is larger than the area of the solder ball pad 3).

The length L2 and the width W2 of the solder ball pad 3 are designed during the design of the LED chip, the length L1 and the width W1 of the pad opening 2 are respectively expanded by 10-50um according to the size of the solder ball pad 3, the ratio a of the length L1 of the pad opening 2 to the length L2 of the solder ball pad 3 is 1.05-1.2, the ratio b of the width W1 of the pad opening 2 to the width W2 of the solder ball pad 3 is 1.03-1.2, the height of the solder ball is the required solder ball height h, and the loss ratio R of the solder paste is generally 80-95%, so h, a, b and R in the formula are known, and the thickness of the printing steel mesh, namely the thickness T2 of the pad opening 2, can be calculated through the formula, namely the thickness of the steel mesh manufactured by a manufacturer needing to print the steel mesh.

The width-to-thickness ratio of the pad opening 2= width W1 of the pad opening 2/thickness T2 of the pad opening 2, and since the width W1 of the pad opening 2 is increased and the thickness T2 of the pad opening 2 is decreased, the width-to-thickness ratio is increased, the larger the width-to-thickness ratio is, the smoother the solder paste is transferred from the steel mesh onto the LED chip, and the lower the anomaly is, the lower the anomaly is

Pad opening 2 in the printing steel mesh in this application is slightly bigger than the tin ball pad, pad opening 2's area is greater than the area of tin ball pad 3 promptly, like this the tin cream can pave fast when printing in pad opening 2, also can be better when the demoulding not remain the tin cream, it is unusual to reduce the tin cream and draw the point printing, the piece source that has the tin cream simultaneously is through the backward flow back, be greater than on 3 marginal parts of tin ball pad tin cream can be gathered back to tin ball pad 3 by whole balls, after the backward flow promptly, the area of the tin cream of final design still equals the area of tin ball pad 3, can not lead to the tin cream to flow back unusually, there is better embodiment to the homogeneity of high density LED chip after printing like this.

The above embodiments are merely illustrative of the technical concepts and features of the present invention, and the purpose of the embodiments is to enable those skilled in the art to understand the contents of the present invention and implement the present invention, and not to limit the protection scope of the present invention. All equivalent changes and modifications made according to the spirit of the present invention should be covered within the protection scope of the present invention.

Claims

1. The utility model provides a LED chip printing steel mesh, includes steel sheet (1) and sets up a plurality of pad openings (2) on steel sheet (101), the shape of each pad opening (2) is the same with the shape of each tin ball pad (3) on waiting to print the LED chip, its characterized in that, the area of each pad opening (2) is greater than the area of each tin ball pad (3), and with the area of pad opening (2) be equal to when the area of each tin ball pad (3) compares, the thickness of printing steel mesh promptly the thickness of pad opening (2) is attenuate, the volume that is located each tin ball pad (3) after the printing backward flow is in the tin ball pad volume of (3) keeps unchangeable.

2. The LED chip printing steel mesh as claimed in claim 1, wherein the area of each pad opening (2) is larger than the area of each tin ball pad (3) by:

and expanding the pad opening (2) by 10-50um outwards by taking the solder ball pad (3) as a center.

3. The LED chip printing steel net according to claim 1, wherein the area of each pad opening (2) is defined to be the same as the area of each tin ball pad (3), the thickness of the pad opening (2) is T1, the area of the pad opening (2) is S1, and the volume of the tin ball on the tin ball pad (3) after printing reflow is V = S1 · T1; when the area of each pad opening (2) is defined to be larger than the area of each tin ball pad (3), the thickness of the pad opening (2) is T2, the area of the pad opening (2) is S2, the volume of the tin ball on the tin ball pad (3) after printing and reflowing is V = S2. T2,

the thickness T2= T1 (1-S1/S2) of the pad opening (2) after the area of the pad opening (2) is increased to S2.

4. The LED chip printing steel net according to claim 3, wherein if the shape of the solder ball pad (3) is rectangular, and defines the height of the solder ball on the solder ball pad (3) after printing reflow as h, the solder paste loss ratio at the time of mold release after printing as R, the ratio of the length L1 of the pad opening (2) to the length L2 of the solder ball pad (3) as a, and the ratio of the width W1 of the pad opening (2) to the width W2 of the solder ball pad (3) as b, then

T2=h/（a·b·R）。

5. The LED chip printing steel net according to claim 4, wherein L1-L2= W1-W2=10-50 um.

6. The LED chip printing steel net according to claim 4, wherein the ratio of the length L1 of the pad opening (2) to the length L2 of the solder ball pad (3) is a = 1.05-1.2;

the ratio b of the width W1 of the pad opening (2) to the width W2 of the solder ball pad (3) is = 1.03-1.2.

7. LED chip printing steel net according to any of claims 1 to 6, characterized in that the number of pad openings (2) on the steel plate is an even number of 2 or more.

8. The LED chip printing steel mesh according to any one of claims 1 to 6, wherein the printing steel mesh is made of Ni material.