TWI772011B - Vacuum reflow method and device - Google Patents

Abstract

The invention provides a vacuum type reflow soldering method. The steps include: preparing a carrier board with solder pads, and arranging solder blocks on the solder pads; placing the carrier board in an accommodating space of a vacuum type reflow soldering device; Under the condition of maintaining the vacuum state of the accommodating space, a laser heating process is performed on the solder block to reflow the solder block; A first opening that communicates with the accommodating space and is closed by a light-transmitting sealing plate and a second opening that is closely arranged with a vacuum suction nozzle, the vacuum suction nozzle is used for connecting vacuum equipment; solder reflow is performed in a vacuum to remove air bubbles in the solder , Avoid the solder offset caused by gas flow, and the laser heating efficiency is high, avoiding the stability and connection quality of the carrier board due to repeated heating.

Description

Vacuum reflow method and device

A reflow method and device, especially a method for vacuum reflow in a vacuum environment and a device used for the method.

A packaged chip product mainly includes a package shell, a chip body (bare die) and a carrier. The chip body is disposed on one surface of the carrier board, and the pins of the chip are connected to the pads on the surface of the carrier board by solder balls, and are electrically connected to the circuit embedded in the carrier board. Another bonding pad on the opposite surface of the carrier board. Wherein, solder balls need to be disposed on the solder pads of the carrier board, and then the solder balls are used to connect the pins of the chip or connect the finished chip to the circuit board.

In order to ensure the effect of fixation and electrical connection between the chip body, the carrier board and the circuit board, how to efficiently and high-quality arrange solder balls on the pads for electrically connecting external contacts is a key process. In the conventional solder ball placement process, solder paste (Solder Print) or solder ball mounting (Ball Mount) can be placed on the pads of the carrier first by printing; then, the solder paste or tin is temporarily adhered. The carrier of the balls is placed in a reflow oven to perform a reflow process (Reflow) to heat the carrier and the solder paste or solder balls on it to melt the solder paste or solder balls; finally, cooling (Cooling) ) the carrier board to fix the solder paste or solder balls on the pads.

However, please refer to FIG. 4A , taking the solder balls 63 as an example, when the solder balls are mounted on the solder pads 62 , there are usually tiny air bubbles 63A in the solder balls 63 ; please refer to FIG. 4B . When the reflow process makes the solid solder balls 63 melt into a liquid state, the tiny air bubbles 63A are in the liquefied solder balls. will flow and gather into larger bubbles, and after cooling, as shown in Figure 4B, the solder balls 63' after reflow retain larger bubbles 63B

The larger air bubbles 63B are likely to cause instability of the welding structure in the subsequent process or the use of the finished product, for example, cracks are formed in the solder due to thermal expansion and contraction during repeated temperature changes. Therefore, the existing carrier board solder ball placement process needs to be further improved.

In view of the problem that the existing solder ball setting method is easy to cause residual bubbles in the solder ball, the present invention provides a vacuum type reflow method, the method includes the following steps: preparing a carrier board with a solder pad; A solder block is arranged on the solder pad of the carrier board; a vacuum type reflow device is prepared, the vacuum type reflow device has an accommodating space, and an accommodating platform is located in the accommodating space; the carrier board is placed in the vacuum type reflow soldering device on the accommodating platform in the reflow device, and expose the solder pad to the accommodating space; perform a vacuuming procedure on the accommodating space to maintain a vacuum state in the accommodating space of the vacuum type reflow device ; Perform a laser heating process on the solder block on the pad to reflow the solder block.

In addition, the present invention provides a vacuum type reflow device for the vacuum type reflow method, which includes: a casing having an accommodating space and an accommodating platform, and the casing is provided with accommodating spaces respectively communicating with the accommodating space. a first opening and a second opening; a light-transmitting sealing plate disposed on the first opening of the casing and closing the first opening; and a vacuum suction nozzle tightly disposed on the second opening of the casing Open your mouth.

The vacuum type reflow unit is used to accommodate the carrier board for the reflow process. The accommodating platform is used for placing the carrier board, and the side of the carrier board on which the solder bumps are disposed is exposed in the accommodating space and faces the first opening. The first opening is closed by the light-transmitting sealing plate, so that the laser light source irradiates the solder block on the carrier board through the first opening for heating. The vacuum suction nozzle is arranged in the second opening and is used for connecting to an external vacuuming device. After the carrier plate is placed on the accommodating platform in the accommodating space, the vacuuming machine is connected to the vacuum suction nozzle to evacuate the accommodating space and maintain its vacuum state.

In the vacuum reflow method of the present invention, the carrier to be reflowed together with the solder blocks pre-set on the solder pads are placed into the accommodating space of the vacuum reflow device, and a vacuum process is performed, and the maintenance When the accommodating space is in a vacuum state, the solder bumps on the solder pads are directly heated by a laser heating procedure. In a vacuum accommodating space, when the solder block is melted into a liquid state, the air bubbles in the solder block will move to the surface of the solder block and escape into the accommodating space due to the vacuum in the accommodating space having a lower air pressure. In this way, when the laser heating process is completed, the air bubbles in the liquid solder are discharged, and after the temperature of the solder block decreases and solidifies, the proportion of air bubbles in the solder block will be greatly reduced, so that the solder block structure after the reflow process is completed is stable. Reduce the risk of cracks in the solder bumps due to temperature changes, different expansion coefficients of solder bumps and bubbles in subsequent processes or use. In addition, since the laser is used to directly heat the solder bumps on the solder pads, rather than the traditional reflow process to bake the entire carrier board, the laser heat energy is mainly concentrated on the solder bumps, and the carrier board itself will not be affected by large-scale or Overall heating reduces the number of times the carrier itself is heated and cooled, and reduces the risk of warpage or circuit damage caused by temperature changes.

11: Carrier board

12: Solder pads

20: Solder bumps

20': Liquid solder bump

20A: Micro bubbles

20B: Bubbles

30: Vacuum reflow device

31: Shell

300: accommodating space

311: accommodating platform

312: The first opening

313: Second Opening

32: Translucent sealing plate

33: Vacuum nozzle

40: Vacuum equipment

50: Laser equipment

61: carrier board

62: Solder pad

63: Tin Ball

63': liquid solder ball

63A: Micro bubbles

63B: Larger bubbles

1A to 1H are schematic flowcharts of the vacuum reflow method of the present invention.

2A to 2C are partial cross-sectional schematic views of the carrier board and the solder bump in the vacuum reflow method of the present invention.

3 is a schematic cross-sectional view of a preferred embodiment of the vacuum type reflow device of the present invention

4A and 4B are schematic partial cross-sectional views of the carrier board and the solder balls in the reflow process of the prior art.

Referring to FIGS. 1A to 1F , the vacuum reflow method of the present invention includes the following steps: as shown in FIG. 1A , prepare a carrier board 11 , a surface of the carrier board 11 is provided with at least one solder pad 12 , FIG. 1A is an example of a plurality of solder pads 12; as shown in FIG. 1B, a solder bump 20 is disposed on the solder pad 12 of the carrier board 11; preferably, the solder bump 20 is formed by a printing process or a planting The ball process is arranged on the solder pads 12 of the carrier board 11 , and the solder block 20 is, for example, a tin block or a tin ball; as shown in FIG. 1C , a vacuum type reflow device 30 is prepared, and the vacuum type reflow device 30 has a An accommodating space 300 has a accommodating platform 311 in the accommodating space 300; as shown in FIG. 1D, the carrier 11 is placed on the accommodating platform 311 in the vacuum type reflow device 30, so that the soldering The pad 12 is exposed in the accommodating space 300; as shown in FIG. 1E, a vacuuming procedure is performed on the accommodating space 300 to maintain a vacuum state in the accommodating space 300 of the vacuum reflow device 30; as shown in FIG. 1F As shown, a laser heating process is performed on the solder bump 20 on the solder pad 12 to reflow the solder bump 20, so that the solder bump 20 is melted into a liquid state and can be attached to the solder pad 12; this one Preferably, a laser device 50 is used to generate a laser beam, and the solder block 20 on the solder pad 12 of the carrier board 10 in the accommodating space 300 is processed by a light-transmitting sealing plate 32 of the vacuum reflow device 30 . warm.

After reflow, as shown in FIG. 1G , the vacuum state of the accommodating space 300 is released; as shown in FIG. 1H , the carrier board 11 is taken out from the accommodating space 300 .

Referring to FIG. 1C , the vacuum type reflow apparatus 30 of the present invention may include a casing 31 , a transparent sealing plate 32 and a vacuum suction nozzle 33 . The housing 31 has an accommodating space 300, and the housing Inside 31 is a receiving platform 311 . The housing 31 has a first opening 312 and a second opening 313 respectively communicating with the accommodating space 300 , and a setting surface of the accommodating platform 311 can face the first opening 312 , and the setting surface is used for placing In the carrier board 11 , the surface of the carrier board 11 provided with the solder bumps 20 faces the first opening 312 . The light-transmitting sealing plate 32 is disposed on the first opening 312 for closing the first opening 312 and allowing the laser light to pass through to illuminate the carrier 1 on the accommodating platform 311 . Preferably, a sealing ring or a sealing tape is arranged between the transparent sealing plate 32 and the first opening 312 , so as to tightly close the first opening 321 and maintain the vacuum state in the accommodating space 300 . Purpose. The vacuum suction nozzle 33 is tightly disposed on the second opening 313 of the casing 31 for connecting to a vacuum device 40 .

In one embodiment, the light-transmitting sealing plate 32 is open and closed at the first opening 321 for inserting or taking out the carrier plate 11 when opening, and closing the first opening 321 to ensure the container. The vacuum state of the storage space 300 is obtained. In another embodiment, the light-transmitting sealing plate 32 is fixedly disposed on the first opening 321 to close the first opening 312 , and a pick-and-place opening (not shown) is further provided on the casing 31 for For inserting and taking out the carrier board 11 . The pick-and-place opening can be set according to the requirements of a jig or a process machine, which is not limited in the present invention.

It should be noted that the "vacuum state" in the present invention refers to a state in which the air pressure in the accommodating space 300 is lower than the atmospheric pressure, as long as the air bubbles in the solder block 12 in the molten state can be moved to the surface due to the pressure difference. That is, the present invention is not limited thereto. Preferably, the vacuum state of the present invention is a vacuum degree of 0.3 atm (standard atmospheric pressure) to 0.5 atm.

Referring to FIG. 2A , when the solder bump 20 is disposed on the solder pad 12 , there will be many tiny air bubbles 20A therein. As shown in FIG. 2B , when the carrier plate 11 is placed in the accommodating space 300 in a vacuum state and melted by laser heating, due to the low-pressure vacuum state in the accommodating space 300 , the micro-bubbles 20A are formed according to the pressure The surface of the solder bump 20 moves differentially and escapes into the accommodating space 300 . When the liquid solder block 20' after the laser heating process is cooled, as shown in FIG. 2C , there will be only a relatively small portion of the solder block 20 . There are very low bubbles or no obvious bubbles, so that the solder bump 20 has stable quality in subsequent soldering and use.

Referring to FIG. 3 , preferably, the vacuum type reflow device 30 further includes a heat insulating pad 34 disposed on the accommodating platform 311 , and the carrier board 11 is disposed on the heat insulating pad 34 . When the laser heating process is performed, the heat insulating pad 34 isolates the carrier 11 from the accommodating platform 311 of the housing 31 to prevent heat energy from being conducted from the solder block 20 to the housing 31 through the solder pad 12 and the body of the carrier 11 , and further Improve the efficiency of the laser heating process.

In addition to the advantages of removing air bubbles in the solder block and reducing the heating of the carrier, the vacuum reflow method and device of the present invention have the following advantages: the laser beam only heats the part of the solder block that needs to be melted, the temperature control is easy, and Due to the non-baking and heating of the entire carrier board, energy waste is reduced and energy efficiency is improved; reflow is performed in a vacuum environment, rather than in a nitrogen environment in traditional reflow technology, so there is no need to consume nitrogen, reducing reflow soldering Process cost; and because it is reflowed in a vacuum environment, the risk of solder bumps shifting due to ambient gas flow is avoided.

To sum up, the vacuum reflow method of the present invention solves the problem of residual air bubbles after the solder bumps are reflowed on the pads, further reduces the risk of repeated heating of the carrier itself, and reduces the reflow process. energy consumption, and improve the stability of the solder bumps that complete the reflow process.

The above are only preferred embodiments of the present invention, and are not intended to limit the present invention in any form. Although the present invention has been disclosed as above with preferred embodiments, it is not intended to limit the present invention. Personnel, within the scope of not departing from the technical solution of the present invention, can make some changes or modifications to equivalent examples of equivalent changes by using the technical content disclosed above, but all content that does not depart from the technical solution of the present invention, according to the present invention Any simple modifications, equivalent changes and modifications made to the above embodiments still fall within the scope of the technical solutions of the present invention.

11: Carrier board

12: Solder pads

20: Solder bumps

31: Shell

300: accommodating space

311: accommodating platform

312: The first opening

32: Translucent sealing plate

33: Vacuum nozzle

40: Vacuum equipment

50: Laser equipment

Claims (5)

A vacuum type reflow soldering method, comprising the following steps: preparing a carrier board with a solder pad; setting a solder block on the solder pad of the carrier board; preparing a vacuum type reflow soldering device; the vacuum type reflow soldering The device comprises a casing and a light-transmitting sealing plate, the casing has an accommodating space and a first opening communicating with the accommodating space, and a accommodating platform is arranged in the accommodating space, and the light-transmitting sealing plate is arranged on the The first opening of the casing is closed and the first opening is closed; the carrier is placed on the accommodating platform in the vacuum reflow device, and the solder pad is exposed in the accommodating space; the accommodating A vacuum process is performed in the space to maintain a vacuum state in the accommodating space of the vacuum type reflow device; a laser heating process is performed on the solder block on the solder pad to make a laser beam pass through the vacuum type reflow device. The light-transmitting sealing plate heats the solder bumps on the solder pads of the carrier in the accommodating space, so as to reflow the solder bumps. The vacuum type reflow method as claimed in claim 1, wherein in the step of disposing a solder bump on the pad of the carrier, the solder bump is disposed on the surface of the carrier by a printing process or a ball-mounting process. on the solder pad. A vacuum type reflow soldering device includes: a casing with an accommodating space and a accommodating platform, the casing has a first opening and a second opening respectively communicating with the accommodating space, and the accommodating The platform is disposed toward the first opening; a light-transmitting sealing plate is disposed on the first opening of the casing and closes the first opening; and a vacuum suction nozzle is tightly disposed on the second opening of the casing. The vacuum type reflow soldering device according to claim 3, wherein a setting surface of the accommodating platform faces the first opening. The vacuum type reflow soldering device according to claim 3 or 4, further comprising: a heat insulating pad disposed on the accommodating platform in the accommodating space.

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