TWI771987B - Method for removing residual solder on circuit substrate - Google Patents

Abstract

Disclosed is a method for removing residual solder on a circuit substrate, comprising: a preheating step of heating tin solder on the circuit substrate as a target to be removed to a temperature to become a molten state; and a removing step of heating to vaporize the tin solder of the molten state, thereby removing the tin solder from the circuit substrate.

Description

Method for removing residual tin on circuit board

The present invention relates to a method for removing residual tin on a circuit substrate, in particular to a method for removing residual tin on a circuit substrate which can effectively avoid damage to electronic components on the circuit substrate.

Defective products are often produced in the production process of circuit substrates, and repairs are required at this time to improve product yield. After the electronic components on the circuit substrate are removed for rework, the conductive tin often remains on the circuit substrate to form tin spots. An oxide layer is usually formed on the surface of the tin point. The melting point of this oxide layer is higher than that of general tin, which is easy to cause poor soldering due to insufficient temperature and the solder is not completely melted during rework, that is, cold soldering. (cold solder), resulting in poor performance of electronic components. For this reason, in order to avoid defects in the rework process, tin spot removal is performed.

In the prior art, the method of removing the tin spot is to apply a high temperature to the tin spot for a long time, so that the tin spot absorbs energy and is heated from normal temperature to melting point, endothermic to melting, and further absorbs heat to vaporization, so as to remove the tin spot . However, during the whole process, the circuit substrate is also continuously affected by the high temperature for heating the tin spot, so that other electronic components on the circuit substrate are easily overheated and damaged.

Therefore, the purpose of the present invention is to provide a method for removing residual tin on a circuit substrate, so as to effectively remove the residual tin on the premise of avoiding damage to other electronic components on the circuit substrate.

The technical means adopted by the present invention to solve the problems of the prior art is to provide a method for removing residual tin on a circuit substrate, which is used to remove a conductive tin spot remaining on a circuit substrate, the method comprising: a preheating the step of heating the conductive tin spot on the circuit substrate as a target to be removed by a preheating heat from an external directivity, so that the conductive tin spot is heated to a preheating temperature and becomes a molten state; and a removal In the step, the conductive tin point preheated to the molten state is further heated to vaporize by an external directivity of heat for vaporization, so as to remove the conductive tin point from the circuit substrate.

In an embodiment of the present invention, a method for removing residual tin on a circuit substrate is provided, wherein in the preheating step, the preheating heat source is gas, and the conductive tin dots are heated to the molten state.

In an embodiment of the present invention, a method for removing residual tin on a circuit substrate is provided, wherein in the preheating step, the heat source for preheating is infrared rays, and the conductive tin dots are heated to the molten state.

In an embodiment of the present invention, a method for removing residual tin on a circuit substrate is provided, wherein in the preheating step, the preheating heat source is a laser, and the conductive tin dots are heated by a laser heating method to the molten state.

In an embodiment of the present invention, a method for removing residual tin on a circuit substrate is provided, wherein the preheating heat source is a gas laser, a solid-state laser, or a semiconductor laser.

In an embodiment of the present invention, a method for removing residual tin on a circuit substrate is provided, wherein in the preheating step, the preheating temperature is a temperature slightly higher than the melting point of the conductive tin point.

In an embodiment of the present invention, a method for removing residual tin on a circuit substrate is provided, wherein in the removing step, the heat source for vaporization is a pulsed laser, and the preheated conductive tin spot is heated by the The pulsed laser is further heated to vaporize in an instant.

In an embodiment of the present invention, a method for removing residual tin on a circuit substrate is provided, wherein in the removing step, the light spot heated by the pulsed laser on the conductive tin spot is smaller than the diameter of the conductive tin spot .

In an embodiment of the present invention, a method for removing residual tin on a circuit substrate is provided, wherein in the removing step, the pulsed laser is a nanosecond pulsed laser, and the preheated conductive tin dots are The nanosecond pulsed laser is further instantly heated to vaporize.

In an embodiment of the present invention, a method for removing residual tin on a circuit substrate is provided, wherein before the preheating step, a pre-step is further included to remove the electronic components on the conductive tin point.

Through the technical means adopted in the present invention, the conductive tin dots to be removed are first heated to a relatively low preheating temperature, so as to prevent damage to the remaining electronic components on the circuit substrate and improve the conductivity in advance. The temperature of the tin point makes the conductive tin point obtain a certain amount of energy in advance. In this way, when the conductive tin spot is removed later, the further energy required to be provided is relatively reduced, so even a relatively short heating time is enough to quickly heat the conductive tin spot to vaporize, and there is no need to worry about the oxidation of the outer layer. The phenomenon of uneven vaporization caused by the influence of uneven heat conduction can effectively reduce the high temperature period, thereby effectively preventing the remaining electronic components on the circuit substrate from being damaged due to overheating.

Embodiments of the present invention will be described below with reference to FIGS. 1 to 5 . This description is not intended to limit the embodiments of the present invention, but is an example of the present invention.

As shown in FIG. 1 and FIG. 2, a method for removing residual tin on a circuit substrate according to an embodiment of the present invention is used to remove a conductive tin spot 2 remaining on a circuit substrate 1, and the method includes: : a preheating step S1 and a clearing step S2.

As shown in FIG. 1 and FIG. 3, according to the method for removing the residual tin on the circuit board according to the embodiment of the present invention, in the preheating step S1, a heat source H1 for preheating is directed against the external directivity by a preheating heat source H1. The conductive tin spot 2 on the circuit substrate 1 as the target to be removed is heated, so that the conductive tin spot 2 is heated to a preheating temperature and becomes a molten state.

In other words, in the preheating step S1, under the premise of not vaporizing the conductive tin spot 2 as the target to be removed and suppressing or avoiding damage to the remaining electronic components 3 on the circuit substrate 1 due to high temperature, the The conductive tin spot 2 is heated to become a molten state, so that the conductive tin spot 2 obtains a certain amount of energy in advance before the subsequent cleaning step S2.

Preferably, the preheating temperature is slightly higher than the melting point of the conductive tin spot 2. For example, when the conductive tin spot 2 is a tin-lead alloy, the melting point is close to 183°C, so the preheating temperature is controlled at 183-185°C as When the conductive tin point 2 is lead-free tin, for example: tin-copper alloy, the melting point is about 277 ℃, so it is better to control the preheating temperature to be slightly higher than 177 ℃; the conductive tin point 2 is a tin-silver alloy When the conductive tin point 2 is a tin-silver-copper alloy, the melting point is about 220°C, so the preheating temperature is controlled to be slightly higher than 220°C. ℃ is better. In addition, since the power required to maintain the conductive tin spot 2 in a molten state varies with the material and size of the conductive tin spot 2, the preheating power of the preheating heat source H1 can be based on the conductive tin spot The material and size of 2 are adjusted. Preferably, as the heat dissipation area of the conductive tin spot 2 is larger, the preheating power is adjusted to be larger in a manner approximately proportional to the surface area of the conductive tin spot 2 . For example, for the conductive tin spot 2 with a diameter of about 0.15 mm, the required preheating power is between 0.5 and 1.5W. When the conductive tin spot 2 increases to a diameter of about 0.6 mm, the required preheating power Then adjust it to about 8~24W.

In the description of the preheating step S1, the directivity refers to that the heat source H1 for preheating locally heats the conductive tin spot 2 on the circuit substrate 1 as the target to be removed, rather than the overall environment ( Including the heating of the circuit substrate 1 and all the electronic components 3 on it to heat the conductive tin spot 2 as the target to be removed, so as to inhibit or avoid damage to the remaining electronic components 3 on the circuit substrate 1 .

It is better to heat the conductive tin spot 2 as a whole, which means to heat the conductive tin spot 2 as a target to be removed together with the interior covered by the oxide outer layer 21 as a whole. Since the oxidized outer layer of the conductive tin dots is not uniform, when the conductive tin dots are heated from the outside by a high-power laser in the conventional technology, uneven vaporization is easily caused due to uneven heat conduction, so that the residual tin cannot be removed evenly. In the present invention, by preheating the conductive tin spot 2 as the target to be removed in the preheating step S1 as a whole, the conductive tin spot 2 can be pre-obtained with a certain amount of energy in advance and raised to a certain temperature, so as to reduce the subsequent arrival of The further energy provided for vaporization can thereby shorten the heating time required for subsequent heating to vaporization, and can also alleviate or avoid the occurrence of uneven vaporization caused by uneven heat conduction during subsequent heating.

Furthermore, as shown in FIG. 3, in the method for removing the residual tin on the circuit substrate of the present embodiment, in the preheating step S1, the preheating heat source H1 is a laser, and the conductive tin spot 2 is a laser. It is heated to the molten state by laser heating. The advantage of laser is that it has good directivity, and the heat generated by it is less likely to affect the periphery.

Further, in the method for removing residual tin on the circuit substrate of this embodiment, the heat source H1 for preheating can be a gas laser, a solid-state laser, or a semiconductor laser, preferably, the used laser wavelength It is 266nm~1064nm. In addition, as mentioned above, the heating temperature of the preheating heat source H1 is relatively low, so there is no need to use a high-power laser for directly heating the residual tin to vaporization in the prior art. The preheating heat source H1 can use Lower power lasers preheat, reducing the chance of adverse thermal effects.

Of course, the present invention is not limited to preheating by laser heating, and other heating methods can also be used as appropriate. For example, in the preheating step S1 , the preheating heat source H1 can be infrared rays, and the conductive tin dots 2 are heated to the preheating temperature by means of infrared heating (eg, infrared radiation heat transfer). When using infrared heating, it is preferable to use infrared with a wavelength of 700 nm to 2.5 um. For another example, in the preheating step S1, the preheating heat source H1 can be a gas, and the conductive tin spot 2 is heated to the preheating temperature by means of hot air heating. In addition, the gas used as the preheating heat source H1 can be air, preferably an inert gas such as nitrogen. The use of an inert gas can avoid further oxidation of the conductive tin dots 2 .

As shown in FIG. 1 , FIG. 4 and FIG. 5 , according to the method for removing residual tin on a circuit substrate according to an embodiment of the present invention, after the preheating step S1 , the removing step S2 is performed. In the clearing step S2, the conductive tin spot 2 preheated to the molten state is further heated to vaporize by a heat source H2 for vaporization from an external directivity, so that the conductive tin spot 2 is automatically heated to vaporize. The circuit substrate 1 is removed.

In other words, in the cleaning step S2, the conductive tin spot 2 that has been preheated is heated to vaporize in a short time at a high temperature.

Specifically, since the conductive tin spot 2 as the target to be cleaned has been preheated, that is, the temperature has been increased to the preheating temperature in advance by obtaining a certain amount of energy, so in the cleaning step S2, the circuit substrate 1 The possible time for the remaining electronic components 3 to be exposed to high temperature can be changed from the conventional technique of heating the conductive tin point 2 from room temperature to melting point, endothermic to melting, and further endothermic to vaporization to the conductive tin point 2. This molten state, which has obtained a certain amount of energy in advance, is heated to vaporization for a relatively short period of time. Therefore, in the cleaning step S2, even if it is affected by uneven heat conduction, the inside of the conductive tin spot 2 covered by the oxidized outer layer 21 is still enough to be heated to vaporization from the preheating temperature in a short time, and it is not easy to have vaporization. uneven phenomenon, so that residual tin can be removed evenly.

As shown in FIG. 4, in the method for removing residual tin on a circuit substrate of this embodiment, in the removing step S2, the heat source H2 for vaporization is a pulse laser, and the preheated conductive tin spot 2 It is further heated to vaporize by the pulsed laser.

Preferably, the light spot heated by the pulsed laser on the conductive tin spot is smaller than the diameter of the conductive tin spot. As shown in FIG. 4 , by controlling the size of the light spot heated by the pulsed laser, the heating efficiency of the conductive tin spot 2 can be improved and the possible impact on the circuit substrate 1 can be effectively reduced.

In addition, in this embodiment, the pulsed laser is a nanosecond pulsed laser, and the preheated conductive tin spot 2 is further instantly heated to vaporization by the nanosecond pulsed laser. In addition to the original good directivity of the laser, the pulsed laser can release a large amount of energy in an instant, and reduce heat generation, so as to effectively shorten the high temperature period, thereby effectively suppressing or avoiding the impact on the circuit substrate 1. The remaining electronic components 3 are damaged. Of course, the selection of the pulsed laser is not limited to the nanosecond pulsed laser, and may further be a picosecond pulsed laser, a femtosecond pulsed laser, or an angstroms of pulsed laser. In addition, the pulsed laser is a green laser with a wavelength of about 355nm in this embodiment, but the present invention is not limited to this, and the wavelength of the pulsed laser can also be, for example: about 266nm, about 532nm, 1062~ 1064nm.

As shown in FIG. 4 , in the method for removing residual tin on the circuit substrate of this embodiment, the removing step S2 is preferably performed after the conductive tin spot 2 is heated to the molten state and the preheating heat source is used. Execution begins before H1 is turned off to end warm-up.

In other words, in this embodiment, the clearing step S2 is started before the preheating is stopped, so as to effectively suppress the conductive tin spot 2 from turning off the preheating heat source H1 to starting the vaporization heat source H2. energy loss. Of course, the present invention is not limited to this, and the clearing step S2 can also be executed after the preheating step S1 ends, or the preheating step S1 can be continuously executed until the clearing step S2 ends.

As shown in FIG. 1 and FIG. 2, in the method for removing the residual tin on the circuit substrate of the present embodiment, before the preheating step S1, a pre-step S0 is further included, which is to remove the conductive tin spot 2 on the electronic components.

Specifically, in the case where there are electronic components (eg, wafers) on the conductive tin spot 2 that is the target to be cleaned, in order to facilitate the subsequent execution of the preheating step S1 and the cleaning step S2, the electronic components will be removed first. Component removed. Of course, in the case that the conductive tin spot 2 as the target to be cleaned has not yet been provided with electronic components or the electronic components have long been absent due to other reasons, the pre-step S0 does not need to be performed.

By the above-mentioned method of removing residual tin on the circuit substrate of the present invention, the conductive tin spot 2 as the target to be removed will first be heated to a relatively low preheating temperature, so as to avoid the damage to the circuit substrate 1. When the other electronic components 3 are damaged, the temperature of the conductive tin spot 2 is increased in advance, so that the conductive tin spot can obtain a certain amount of energy in advance. In this way, when the conductive tin spot 2 is removed later, the further energy required to be provided is relatively reduced, so even a relatively short heating time is sufficient to quickly heat the conductive tin spot 2 to vaporize, and there is no need to worry The non-uniform vaporization phenomenon caused by the non-uniform thermal conduction of the oxide outer layer 21 effectively reduces the high temperature period, thereby effectively preventing the remaining electronic components 3 on the circuit substrate 1 from being damaged due to overheating.

The above descriptions and descriptions are only descriptions of preferred embodiments of the present invention. Those with ordinary knowledge in the art can make other modifications according to the scope of the patent application defined below and the above descriptions, but these modifications should still be It is within the scope of the right of the present invention for the inventive spirit of the present invention.

1: circuit board 2: Conductive tin point 21: Oxidized outer layer 3: Electronic components H1: Heat source for preheating H2: Heat source for vaporization S0: Preliminary step S1: Preheating step S2: Clear Step

[FIG. 1] is a schematic flowchart showing a method for removing residual tin on a circuit substrate according to an embodiment of the present invention; [FIG. 2] is a schematic diagram showing the pre-steps of a method for removing residual tin on a circuit substrate according to an embodiment of the present invention; [FIG. 3] is a schematic diagram showing a preheating step of a method for removing residual tin on a circuit substrate according to an embodiment of the present invention; [FIG. 4 and FIG. 5] are schematic diagrams showing removal steps of a method for removing residual tin on a circuit substrate according to an embodiment of the present invention.

S0: Preliminary step

S1: Preheating step

S2: Clear Step

Claims (10)

A method for removing residual tin on a circuit substrate is used to remove a conductive tin spot remaining on a circuit substrate, the method comprising: a preheating step, heating the conductive tin spot on the circuit substrate as a target to be removed by a preheating heat from an external directivity, so that the conductive tin spot is heated to a preheating temperature and becomes a molten state; as well as In a removing step, the conductive tin spot preheated to the molten state is further heated to vaporize by an external directivity of heat for vaporization, so as to remove the conductive tin spot from the circuit substrate. The method for removing residual tin on a circuit substrate according to claim 1, wherein in the preheating step, the heat source for preheating is a laser, and the conductive tin dots are heated to the molten state by means of laser heating . The method for removing residual tin on a circuit substrate according to claim 1, wherein in the preheating step, the heat source for preheating is infrared rays, and the conductive tin dots are heated to the molten state by infrared heating. The method for removing residual tin on a circuit substrate according to claim 1, wherein in the preheating step, the preheating heat source is gas, and the conductive tin dots are heated to the molten state by hot air heating. The method for removing residual tin on a circuit substrate according to claim 2, wherein the preheating heat source is a gas laser, a solid-state laser, or a semiconductor laser. The method for removing residual tin on a circuit substrate according to any one of claims 1 to 5, wherein in the preheating step, the preheating temperature is a temperature slightly higher than the melting point of the conductive tin point. The method for removing residual tin on a circuit substrate according to claim 1, wherein in the removing step, the heat source for vaporization is a pulsed laser, and the preheated conductive tin dots are removed by the pulsed laser It is further heated to vaporize instantaneously. The method for removing residual tin on a circuit substrate according to claim 7, wherein in the removing step, the light spot heated by the pulsed laser on the conductive tin spot is smaller than the diameter of the conductive tin spot. The method for removing residual tin on a circuit substrate according to claim 7 or 8, wherein in the removing step, the pulsed laser is a nanosecond pulsed laser, and the preheated conductive tin spot is The nanosecond pulsed laser is further instantly heated to vaporize. The method for removing residual tin on a circuit substrate as claimed in claim 1, further comprising a pre-step before the preheating step for removing electronic components on the conductive tin points.

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