Method for increasing balling rate of metal convex block in vacuum backflow technology

A technology of vacuum reflow and metal bumps, which is applied in the manufacture of electrical components, electrical solid devices, semiconductor/solid devices, etc., can solve the problem of low ball forming rate, and achieve the effect of improving roughness and improving low ball forming rate

Active Publication Date: 2015-04-01

NANTONG FUJITSU MICROELECTRONICS

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AI-Extracted Technical Summary

Problems solved by technology

[0006] In order to overcome the problem of low ball forming rate of metal bumps in the vacuum reflow process existing in the prior art, the present invention p...

Method used

Fig. 1 is the surface image of the tin-lead ball without cleaning before reflow; Fig. 2 is the surface image of the tin-lead bump without brush cleaning before reflow without being balled after reflow; Fig. 3 is before reflow thro...

Abstract

The invention provides a method for increasing the balling rate of a metal convex block in a vacuum backflow technology in the field of semiconductor encapsulation. The method specifically comprises the following steps: (1) allowing a spherical or square metal welding flux convex block to form on a UBM (under bump metal); (2) cleaning the metal welding flux convex block prepared in the step (1) by a hairbrush; (3) putting the metal welding flux convex block treated in the step (2) into a vacuum backflow furnace for backflow; (4) cooling the metal convex block subjected to backflow in the step (3) to the temperature lower than 40 DEG C under a vacuum condition. According to the method disclosed by the invention, the problem of low balling rate of the metal convex block in the vacuum backflow technology can be solved, and the balling rate is increased from 99.5 to 99.98 percent; meanwhile, the surface roughness of a balled metal convex block is also effectively improved.

Application Domain

Solid-state devicesSemiconductor/solid-state device manufacturing +1

Technology Topic

BackflowMetal +2

Image

Examples

Experimental program(4)

Example Embodiment

[0022] Example 1

[0023] A method for improving the ball formation rate of metal lead bumps in a vacuum reflow process includes the following steps:

[0024] (1) Form spherical or square metal solder bumps on UBM (under bump metal);

[0025] (2) Cleaning the metal solder bumps prepared in step (1) through a brush;

[0026] (3) Place the metal solder bumps processed in step (2) in a vacuum reflow oven for reflow;

[0027] (4) The metal solder bumps after reflow in step (3) are cooled to below 40°C under vacuum conditions.

[0028] Among them, the metal solder bumps in step (1) are tin-lead bumps, and the method for forming the tin-lead bumps is electroplating. The preparation method is to deposit the bottom metal layer of the bumps on the wafer by sputtering. Then cover a layer of photoresist layer on the bottom metal layer of the bumps, perform exposure and development to form the area of the solder bumps, and then electroplating the solder, removing the photoresist and etching.

[0029] In step (2), the cleaning time of the brush is 30-240 seconds. Table 1 shows the relationship between the cleaning time of the brush and the ball formation of the metal bump in this embodiment.

[0030] Table 1 The relationship between brush cleaning time and metal bump ball formation rate

[0031] Cleaning time

[0032] It can be seen from the data in the table that the washing time of 120 seconds is the best cleaning process parameter.

[0033] The brush in the step (2) is a nylon brush roller. The brush roller generally has five methods: steel belt winding, weaving, slotted embedded, round hole embedded, and rubber plate embedded. In this experiment, the three methods of steel belt winding, weaving and round hole embedded are mainly used. The experimental results obtained by cleaning with the brush roller of these three methods are not much different. The brush roller used in the test is mainly nylon brush, and the nylon needle of the brush contains silicon carbide. The particle size of silicon carbide can be 180 mesh, 240 mesh, 320 mesh, 400 mesh, 500 mesh, 600 mesh, 800 mesh. , 1000 mesh, 1200 mesh, 1500 mesh, 2000 mesh, the results of the experiment surface when the silicon carbide particle size in the brush is 2000 mesh, the best effect.

[0034] In the step (3), the reflow temperature of the vacuum reflow furnace is 180-240°C. During reflow, the reflow temperature is set according to a certain gradient, and the reflow temperature curve is approximately parabolic, that is, the first temperature is relatively low. Then the temperature rises slowly in a gradient, and when the maximum temperature is reached, the temperature is gradually reduced. The setting of the specific reflow temperature needs to be set according to the properties of the metal bumps and the process parameters of the vacuum reflow furnace. Generally speaking, the processing temperature of the lead-tin bumps is usually 210°C-220°C, while the processing temperature of the tin-silver bumps The peak value is at least 235-245°C. The higher the temperature, the longer the processing time. The six step temperatures in this embodiment are 180°C, 190°C, 205°C, 220°C, 210°C, and 190°C, and the reflux time is 3 minutes.

[0035] Compared with the prior art, the present invention has the following beneficial effects: the problem of low spheroidizing rate of metal bumps in the vacuum reflow process is improved, and the spheroidizing rate is increased from 99.5% to 99.98%. The appearance of the metal bumps after reflow is as specific as figure 1 , 2 , 3 shown.

[0036] Such as figure 1 It is the surface image of the tin lead ball that has not been cleaned before reflow; figure 2 It is the surface image of tin-lead bumps that have not been cleaned by a brush before reflow and are not balled after reflow; image 3 It is the surface image of the tin-lead bumps that have been cleaned by a brush before reflow. It can be seen from the above three figures that the reflow after the brush treatment also effectively improves the surface roughness of the tin-lead bumps after ball formation.

Example Embodiment

[0037] Example 2

[0038] A method for improving the spheroidization rate of metal lead bumps in a vacuum reflow process is characterized by including the following steps:

[0039] (1) Form spherical or square metal solder bumps on UBM (under bump metal);

[0040] (2) Cleaning the metal solder bumps prepared in step (1) through a brush;

[0041] (3) Place the metal solder bumps processed in step (2) in a vacuum reflow oven for reflow;

[0042] (4) The metal solder bumps reflowed in step (3) are cooled to below 40°C under vacuum conditions.

[0043] Wherein, the metal solder bumps in step (1) are tin-silver bumps, and the method for forming the tin-silver bumps is electroplating, and the preparation method is the same as that of the foregoing embodiment 1.

[0044] In step (2), the cleaning time of the brush is 120 seconds, and the brush is a steel belt wound nylon brush roller containing 2000 mesh alumina in the brush.

[0045] In step (3), the reflow temperature of the vacuum reflow oven is 180-240℃. During reflow, the reflow temperature is set according to a certain gradient. The reflow temperature curve is approximately parabolic, and the set 6 step temperatures are in turn 180°C, 190°C, 215°C, 235°C, 215°C, 190°C, the reflux time is 3min.

Example Embodiment

[0046] Example 3

[0047] A method for improving the spheroidization rate of metal lead bumps in a vacuum reflow process is characterized by including the following steps:

[0048] (1) Form spherical or square metal solder bumps on UBM (under bump metal);

[0049] (2) Cleaning the metal solder bumps prepared in step (1) through a brush;

[0050] (3) Place the metal solder bumps processed in step (2) in a vacuum reflow oven for reflow;

[0051] (4) The metal bumps reflowed in step (3) are cooled to below 40°C under vacuum conditions.

[0052] Wherein, the metal solder bumps in step (1) are tin-lead or tin-silver bumps, and the method of forming the tin-lead or tin-silver bumps is the nail-head bump method.

[0053] In step (2), the cleaning time of the brush is 120 seconds, and the brush is a round hole embedded nylon brush roller containing 1500 mesh silicon carbide in the brush.

[0054] In step (3), the reflow temperature of the vacuum reflow furnace is 180-240°C. During reflow, the reflow temperature is set according to a certain gradient, the reflow temperature curve is approximately parabolic, and the reflow time is 3 minutes.

PUM

Property	Measurement	Unit
Granularity	180.0 ~ 2000.0	mesh

Description & Claims & Application Information

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Classification and recommendation of technical efficacy words

Improve roughness

Method for increasing balling rate of metal convex block in vacuum backflow technology

A technology of vacuum reflow and metal bumps, which is applied in the manufacture of electrical components, electrical solid devices, semiconductor/solid devices, etc., can solve the problem of low ball forming rate, and achieve the effect of improving roughness and improving low ball forming rate

AI-Extracted Technical Summary

Problems solved by technology

Method used

Abstract

Image

Examples

Example Embodiment

Example Embodiment

Example Embodiment

PUM

Description & Claims & Application Information

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