JP4159213B2 - Flip chip mounting method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a flip chip mounting method and relates to mounting by Au-Au connection.
[0002]
[Prior art]
In recent years, electronic devices have become more prone to attract new demand by improving performance or reducing size and weight, and the shape of electronic components, the board on which the components are mounted, and the mounting method are mutually related. It has changed greatly to meet the requirements. Flip chip mounting is in line with this trend, and the pitch between the electrodes of the chip is becoming increasingly narrow. Under such circumstances, mounting by Au-Au connection capable of narrow pitch mounting without using solder has been established.
[0003]
FIG. 3A shows a general method for mounting the flip chip on the substrate by Au—Au connection. Gold bumps 3 are formed on the electrodes 2 of the flip chip 1, leveling is performed to align the bump heights, and an insulating paste 7 is applied to the inner periphery of the pad row of the substrate 4 with a dispenser, etc. The gold bumps 3 of the flip chip 1 are pressed and heated on the pads 5 for a predetermined time, and the gold bumps 3 and the gold plating pads 5 are pressed against each other by shrinkage hardening accompanying cooling of the insulating paste 7 to achieve electrical connection. Is.
[0004]
[Problems to be solved by the invention]
However, the mounting method has no problem when the finish of the substrate and the finish of the gold bumps of the flip chip are ideal, but in reality, there are variations in the warp of the substrate and the height of the gold bumps, so FIG. Thus, there is a possibility that the connection failure 11 may occur, and there is a problem that connection reliability is impaired.
The present invention has been made to solve the above problems, and provides a flip chip mounting method that ensures stable connection even if the substrate is warped or the flip chip gold bump height is uneven. Objective.
[0005]
[Means for Solving the Problems]
The flip chip mounting method according to claim 1 is a flip chip mounting method in which a gold bump is formed on a flip chip electrode, an insulating paste is dispensed on a substrate, and the flip chip is heated and pressed on a substrate pad . It consists of a process and is characterized in that the contact surface is increased by deforming each bump .
a) forming a gold bump on the substrate pad by a wire bumping method
b) A step of forming a recess in the central portion of the gold bump formed in the above step.
c) Forming gold bumps on the flip chip electrode by wire bumping
d) Dispensing the insulating paste on the inner periphery of the substrate pad
e) aligning the flip chip with the substrate pad and heating under pressure;
According to the flip chip mounting method of the first aspect, even if the gold bump formed on the flip chip electrode lacks the uniformity of the height , the tip of the gold bump having a dent in the central portion on the substrate pad is sharpened. Further, since the gold bumps on the flip-chip electrode are pressed, the bumps are deformed to increase the contact surface, so that reliable electrical connection of all terminals can be achieved.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a schematic side view showing an embodiment of the present invention. FIG. 1 (a) shows a shape before connection, and FIG. 1 (b) shows a shape after connection. 1 is a flip chip, 2 is an electrode of the flip chip 1, 3 is a gold bump formed on the electrode 2, 4 is a substrate, and 5 is a pad formed on the substrate 4 at a position corresponding to the electrode 2 of the flip chip 1. Gold-plated, 6 is a gold bump bumped on the pad 5 and the center is recessed by a tool, and 7 is an insulating paste.
[0008]
An embodiment of the mounting method when the diameter of the flip chip electrode 2 and the diameter of the substrate pad 5 are set to 100 μm will be described with reference to FIG. In FIG. 2A, a gold bump 6 is formed on a pad 5 of a substrate 4 plated with gold having a thickness of 0.3 μm by a wire bumping method using a gold wire with a diameter of 25 μm. The tip is flattened, and as shown in FIG. 2B, the flattened gold bump 6 is further pressurized at about 80 g using a needle-like tool 9 having a tip diameter of 36 μm to form a concave depression.
Next, as shown in FIG. 2 (c), gold bumps 3 are formed on the flip-chip electrodes 2 by a wire bumping method using a gold wire with a diameter of 25 .mu.m, and as shown in FIG. Insulation paste 7 is applied to the inner periphery of the substrate 10 by a dispensing method, and the flip chip bumps 3 and the substrate pads 5 in FIG. 2 (e) are aligned. Heat at a pressure of 70 g per piece for 15 seconds at 250 ° C.
[0009]
Since the gold bump 3 on the flip chip electrode having a sharp tip is pressed against the gold bump 6 having a recess in the center on the substrate pad, the bumps are deformed to increase the contact surface. Further, the insulating paste 7 is cured while shrinking, so that the bumps are fixed in a pressed state, and an excellent electrical contact is obtained.
The above actual numerical values are only examples, and optimum values are selected according to differences in conditions such as electrode dimensions and bump forming gold wire diameters.
[0010]
【The invention's effect】
According to the present invention, gold bumps are formed on both the flip chip electrode side and the substrate pad side, and further, the gold bump shape is convex on the flip chip electrode side and concave on the substrate pad side. Even if there is variation in bump height, the contact area when both gold bumps are pressed is large, and the electrical and physical connection is reliable, enabling highly reliable flip chip mounting.
[Brief description of the drawings]
FIG. 1 is a schematic side view showing an embodiment of the present invention.
(A) Shape before connection (b) Shape after connection [FIG. 2] FIG. 2 shows an embodiment of the mounting method according to the present invention.
(A) Gold bumps are formed on a substrate pad, and the tip is flattened by leveling. (B) A concave depression is formed in the gold bump on the substrate pad. (C) Gold bump is formed on the flip chip electrode. (D) Insulation paste is applied to the inner periphery of the pad row (e) The bumps of the flip chip are aligned with the pads of the substrate and heated under pressure. It is a side surface schematic diagram which shows chip mounting.
(A) Normal connection state (b) Bad connection state [Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Flip chip 2 Flip chip electrode 3 Gold bump formed on flip chip electrode 4 Substrate 5 Substrate pad (gold plating)
6 Gold bump bumped on the pad of the board and recessed in the center with a tool 7 Insulating paste 8 Leveling tool 9 Needle-shaped tool 10 Pad row 11 Connection failure

Claims (1)

A flip chip mounting method in which a gold bump is formed on a flip chip electrode, an insulating paste is dispensed on a substrate, and the flip chip is heated and pressed on a substrate pad. The flip chip mounting method includes the following steps, and each bump is deformed. And increasing the contact surface .
a) forming a gold bump on the substrate pad by a wire bumping method
b) A step of forming a recess in the central portion of the gold bump formed in the above step.
c) Forming gold bumps on the flip chip electrode by wire bumping
d) Dispensing the insulating paste on the inner periphery of the substrate pad
e) aligning the flip chip with the substrate pad and heating under pressure

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