CN115226315A

CN115226315A - Method for removing residual tin on circuit substrate

Info

Publication number: CN115226315A
Application number: CN202110512482.9A
Authority: CN
Inventors: 卢彦豪
Original assignee: SOTE TECHNOLOGY CO LTD
Current assignee: SOTE TECHNOLOGY CO LTD
Priority date: 2021-04-16
Filing date: 2021-05-11
Publication date: 2022-10-21
Also published as: TW202243562A; TWI771987B

Abstract

The invention relates to a method for removing residual tin on a circuit substrate, which comprises the following steps: a preheating step, heating the conductive tin points on the circuit substrate as the target to be removed to a preheating temperature to be in a molten state; and a cleaning step of heating the entire conductive tin point preheated to the molten state to be vaporized so as to clean the conductive tin point from the circuit substrate.

Description

Method for removing residual tin on circuit substrate

Technical Field

The invention relates to the technical field of methods 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 damaging electronic components on the circuit substrate.

Background

The circuit substrate often has defective products during the manufacturing process, and the defective products need to be repaired to improve the yield of the products. After the electronic components on the circuit substrate are removed by the repair, the conductive tin often remains on the circuit substrate to form tin dots. An oxide layer is usually formed on the surface of the tin spot, and the melting point of the oxide layer is higher than that of general tin, so that poor welding, i.e. cold welding (cold solder), caused by incomplete melting of solder due to insufficient temperature is easily caused during rework, and the performance of the electronic component is further poor. For this reason, in order to avoid the defect of the rework process, the tin spot is removed.

In the prior art, the tin spot is removed by applying a high temperature to the tin spot for a long time, so that the tin spot absorbs energy and is heated from a normal temperature to a melting point, absorbs heat to be molten, and further absorbs heat to be vaporized, thereby removing the tin spot. However, during this entire process, the circuit board is also continuously affected by the high temperature of the tin spot, and the rest of the electronic components on the circuit board are also easily damaged due to overheating.

Disclosure of Invention

Therefore, an object 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 the rest of electronic components on the circuit substrate.

The present invention provides a method for removing residual tin on a circuit substrate, which is used for removing a conductive tin spot remaining on a circuit substrate, and comprises the following steps: a preheating step of heating the conductive tin point serving as the target to be removed on the circuit substrate by a preheating heat source from the outside in a directional manner so that the conductive tin point is heated to a preheating temperature and becomes a molten state; and a removing step of further heating the conductive tin spot preheated to the molten state from the outside in an instant heating manner by a heat source for vaporization to remove the conductive tin spot from the circuit substrate.

In one 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 gas, and the conductive tin spot is heated to the molten state by hot air heating.

In one 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 spot is heated to the molten state by infrared ray heating.

In one 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 spot is heated to the molten state by laser heating.

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

In one 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 one 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 pulse laser, and the preheated conductive tin spot is further instantaneously heated to be vaporized by the pulse laser.

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

In one 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 spot is further instantaneously heated to be vaporized by the nanosecond pulsed laser.

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

By the technical means adopted by the invention, the conductive tin point serving as the target to be cleaned is heated to the preheating temperature with relatively low temperature, so that the temperature of the conductive tin point is increased in advance under the condition of avoiding damaging other electronic components on the circuit substrate, and the conductive tin point obtains certain energy in advance. Therefore, when the conductive tin point is removed, the energy required to be further provided is relatively reduced, so that even if the heating time is relatively short, the conductive tin point can be quickly heated to be vaporized, and the phenomenon of uneven vaporization caused by the influence of uneven heat conduction of the oxidized outer layer is not needed to be worried about, so that the high-temperature time period is effectively reduced, and the damage of other electronic components on the circuit substrate caused by overheating is effectively avoided.

Drawings

Fig. 1 is a flowchart illustrating a method for removing residual tin on a circuit substrate according to an embodiment of the invention.

Fig. 2 is a schematic diagram illustrating a pre-step of a method for removing residual tin on a circuit substrate according to an embodiment of the invention.

Fig. 3 is a schematic diagram illustrating a preheating step of a method for removing residual tin on a circuit substrate according to an embodiment of the invention.

Fig. 4 is a schematic diagram illustrating a cleaning step of the method for cleaning residual tin on the circuit substrate according to the embodiment of the invention.

Fig. 5 is another schematic diagram of the cleaning step of the method for cleaning the residual tin on the circuit substrate according to the embodiment of the invention.

Reference numerals

1. Circuit board

2. Conductive tin point

21. Outer layer of oxidation

3. Electronic assembly

H1 Heat source for preheating

H2 Heat source for vaporization

S0 Pre-step

S1 preheating step

S2 cleaning step

Detailed Description

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

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

As shown in fig. 1 and fig. 3, in the preheating step S1, in order to heat the conductive tin spot 2 on the circuit substrate 1, which is the target to be cleaned, from the outside by means of a preheating heat source H1, the conductive tin spot 2 is heated to a preheating temperature and is in a molten state.

In other words, in the preheating step S1, the conductive tin dots 2 are heated to a molten state under the premise that the conductive tin dots 2 targeted for cleaning are not vaporized and damage to the rest of the electronic components 3 on the circuit substrate 1 due to high temperature is suppressed or avoided, so that the conductive tin dots 2 obtain 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 dots 2, such as: when the conductive tin point 2 is tin-lead alloy, the melting point is close to 183 ℃, so the preheating temperature is preferably controlled to be 183-185 ℃; when the conductive tin dots 2 are lead-free tin, for example: the melting point of the tin-copper alloy is about 277 ℃, so the preheating temperature is preferably controlled to be slightly higher than 177 ℃; when the conductive tin spot 2 is made of tin-silver alloy, the melting point is about 221 ℃, so the preheating temperature is preferably controlled at 221 ℃; when the conductive tin spot 2 is made of tin-silver-copper alloy, the melting point is about 220 ℃, so the preheating temperature is preferably controlled to be slightly higher than 220 ℃. In addition, since the power required to maintain the molten state of the conductive tin dots 2 varies with the material and size of the conductive tin dots 2, the preheating power of the preheating heat source H1 can be adjusted according to the material and size of the conductive tin dots 2, and preferably, the preheating power is adjusted to be larger in approximate proportion to the surface area of the conductive tin dots 2 as the heat dissipation area of the conductive tin dots 2 is larger. For example, the required preheating power is between 0.5 and 1.5W for the conductive tin spot 2 having a diameter of about 0.15mm, and the required preheating power is adjusted to about 8 to 24W when the conductive tin spot 2 is increased to a diameter of about 0.6 mm.

In the description of the preheating step S1, the directional heat source H1 is used for heating the conductive solder dots 2 to be removed on the circuit substrate 1 locally, rather than heating the conductive solder dots 2 to be removed by heating the entire environment (including the circuit substrate 1 and all the electronic components 3 thereon), so as to suppress or avoid damage to the rest of the electronic components 3 on the circuit substrate 1.

The heating of the conductive tin dots 2 is preferably bulk heating, which means that the conductive tin dots 2 targeted for removal are heated together with the inner bulk covered by the oxidized outer layer 21. Because the oxidized outer layer of the conductive tin point is not uniform, when the conductive tin point is heated from the outside by using high-power laser in the prior art, the vaporization is not uniform easily due to uneven heat conduction, so that residual tin cannot be removed uniformly. In the preheating step S1, the whole conductive tin spot 2 to be removed is preheated, so that the whole conductive tin spot 2 can obtain a certain amount of energy in advance and be heated to a certain temperature, and the further supply of energy required for vaporization in the subsequent process is reduced, thereby shortening the heating time required for vaporization in the subsequent process, and relieving or avoiding the occurrence of uneven vaporization caused by uneven heat conduction in the subsequent process.

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

Further, in the method of removing residual tin on the circuit substrate of the present embodiment, the heat source H1 for preheating may be a gas laser, a solid laser, or a semiconductor laser, and preferably, the wavelength of the laser used is 266nm to 1064nm. Further, as described above, since the heating temperature of the heat source H1 for preheating is relatively low, it is not necessary to use a high-power laser beam which is conventionally used to directly heat the residual tin to be vaporized, and the heat source H1 for preheating can be preheated by a laser beam of a relatively low power, thereby reducing the chance of causing an adverse thermal influence.

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

As shown in fig. 1, 4 and 5, the method for removing residual tin on a circuit substrate according to an embodiment of the present invention performs the removing step S2 after the preheating step S1. In the cleaning step S2, the conductive solder dot 2 is further heated to be vaporized by a heat source H2 for vaporization from the outside in a directional manner with respect to the conductive solder dot 2 preheated to the molten state, so as to clean the conductive solder dot 2 from the circuit substrate 1.

In other words, in the removing step S2, the conductive tin dots 2 that have been preheated are heated to be vaporized at a high temperature in a short time.

Specifically, since the conductive tin spot 2 as an object to be cleaned has been preheated, i.e., has acquired a certain amount of energy to have its temperature increased to the preheating temperature in advance, the possible time for the remaining electronic components 3 on the circuit substrate 1 to be brought into contact with a high temperature in the cleaning step S2 can be changed from a long time in the prior art in which the conductive tin spot is heated from normal temperature to a melting point, absorbs heat to melting, and further absorbs heat to vaporization to a relatively short time in which the conductive tin spot 2 is heated from the molten state to vaporization from which a certain amount of energy has been acquired in advance. Therefore, in the removing step S2, even if the influence of the uneven heat conduction is received, the inside of the conductive tin spot 2 covered with the oxidized outer layer 21 is heated to be vaporized from the preheating temperature in a short time, and the uneven vaporization is not easily generated, so that the residual tin can be removed evenly.

As shown in fig. 4, in the method for removing residual tin on the circuit substrate of the present embodiment, in the removing step S2, the heat source H2 for vaporization is a pulse laser, and the preheated conductive tin spot 2 is further instantaneously heated to be vaporized by the pulse laser.

Preferably, the spot of the pulsed laser heating 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 spot heated by the pulse laser, the heating efficiency of the conductive solder dot 2 can be improved and the influence on the circuit board 1 can be effectively reduced.

In addition, in the present embodiment, the pulse laser is a nanosecond pulse laser, and the preheated conductive tin spot 2 is further instantaneously heated to be vaporized by the nanosecond pulse laser. The pulse laser has the advantage of good directivity of the laser, and can instantly release large energy and reduce heat generation, so as to effectively shorten the high temperature period, thereby effectively inhibiting or avoiding damage to the rest of electronic components 3 on the circuit substrate 1. Of course, the selection of the pulse laser is not limited to the nanosecond pulse laser, and may further be a picosecond pulse laser, a femtosecond pulse laser, or an angstrom second pulse laser. In addition, the pulse laser is a green laser with a wavelength of about 355nm in the present embodiment, but the invention is not limited thereto, and the wavelength of the pulse laser may be, for example: about 266nm, about 532nm, 1062-1064 nm.

As shown in fig. 4, in the method for removing residual tin on a circuit substrate of the present embodiment, the removing step S2 is preferably performed after the conductive tin spot 2 is heated to the molten state and before the preheating heat source H1 is turned off to end preheating.

In other words, in the present embodiment, the purging step S2 is performed before the preheating is stopped, so as to effectively suppress the energy loss of the conductive tin spot 2 during the period from the turning off of the preheating heat source H1 to the turning on of the vaporizing heat source H2. Of course, the present invention is not limited thereto, and the clearing step S2 may be started after the preheating step S1 is finished, or the preheating step S1 may be continuously executed until the clearing step S2 is finished.

As shown in fig. 1 and 2, the method for removing residual tin on a circuit substrate of the present embodiment further includes a pre-step S0 for removing the electronic component on the conductive tin spot 2 before the pre-heating step S1.

Specifically, in the case where an electronic component (e.g., a chip) exists on the conductive solder bump 2 as a target to be cleaned, the electronic component is removed first to facilitate the subsequent preheating step S1 and the cleaning step S2. Of course, if no electronic component is disposed on the conductive solder dots 2 to be cleaned or if no electronic component is present for other reasons, the pre-step S0 is not required.

By the method for removing residual tin on the circuit substrate, the conductive tin point 2 to be removed is heated to a preheating temperature with a relatively low temperature, so that the temperature of the conductive tin point 2 is increased in advance under the condition of avoiding damage to other electronic components 3 on the circuit substrate 1, and the conductive tin point obtains certain energy in advance. Therefore, the energy required to be further provided is relatively reduced when the conductive tin spot 2 is removed, so that even if the heating time is relatively short, the conductive tin spot 2 can be rapidly heated to be vaporized without worrying about the uneven vaporization caused by the influence of the uneven heat conduction of the oxidized outer layer 21, thereby effectively reducing the high temperature period and effectively avoiding the damage of the rest electronic components 3 on the circuit substrate 1 due to overheating.

While the foregoing description and description are directed to the preferred embodiment of the present invention, other and further modifications may be devised by those skilled in the art based on the teachings herein.

Claims

1. A method for removing residual tin on a circuit substrate, the method being used for removing conductive tin spots remaining on the circuit substrate, the method comprising:

a preheating step of heating the conductive tin dots serving as targets to be removed on the circuit substrate by using a preheating heat source from outside directivity, so that the conductive tin dots are heated to a preheating temperature and become a molten state; and

a removing step of heating the conductive tin spot preheated to the melting state from the outside in an instantaneous heating manner by a heat source for vaporization so as to remove the conductive tin spot from the circuit substrate.

2. The method of claim 1, wherein in the preheating step, the preheating heat source is a laser, and the conductive tin spot is heated to the molten state by laser heating.

3. The method as claimed in 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 rays.

4. The method as claimed in claim 1, wherein in the preheating step, the preheating heat source is a gas, and the conductive tin dots are heated to the molten state by hot air heating.

5. The method of claim 2, wherein the heat source for preheating is a gas laser, a solid laser or a semiconductor laser.

6. 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 dots.

7. The method of claim 1, wherein in the step of removing, the heat source for vaporization is a pulsed laser, and the preheated conductive tin spot is further heated to be vaporized instantaneously by the pulsed laser.

8. The method as claimed in claim 7, wherein the spot heated by the pulsed laser is smaller than the diameter of the conductive tin spot.

9. The method of claim 7 or 8, wherein in the step of removing, the pulsed laser is a nanosecond pulsed laser, and the preheated conductive tin spot is further instantaneously heated to be vaporized by the nanosecond pulsed laser.

10. The method of claim 1, further comprising a pre-step of removing electronic components from the conductive tin dots prior to the pre-heating step.