A method for heating and separating a PCB board and a surface-mount crystal oscillator

Abstract

This application discloses a method for heating and separating a PCB board and a surface-mount crystal oscillator, which belongs to the field of semiconductors. The technical point is that the area S used to separate the crystal oscillator is not greater than 5mm. 2 The crystal oscillator includes the following steps: Step 1: Use high-temperature insulation tape to wrap the front of the PCB (the crystal oscillator is also wrapped in advance); Step 2: Cut the tape just above the crystal oscillator position to leave a gap; Step 3: The back of the PCB is in contact with the heat dissipation module through the thermal conductive silicone sheet; Step 4: Heat; Step 5: After the soldering pad tin melts, move the vacuum nozzle to the center of the crystal oscillator cover, contact the cover, vacuum adsorb, and then peel off the crystal oscillator. The method of this application can effectively solve the problem of crystal oscillator area S not greater than 5mm 2 There are several problems that arise when thermally separating the crystal from the PCB.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor components, and more particularly to a method for heating and separating a PCB board and a surface-mount crystal oscillator. Background Art

[0002] <Traditional method of separating PCB and SMD crystal oscillator>

[0003] Traditional methods for separating PCB and SMD crystal oscillators include the following methods (cited from: https: / / www.sohu.com / a / 333673094_99903008):

[0004] The first method is the electric soldering iron heating separation method. Figure 1 , Attachment Figure 2 As shown, the method includes the following steps:

[0005] S100: Choose a flat spade or knife-edge soldering iron tip. Adjust the soldering iron temperature according to the type of PCB solder paste. For low-temperature solder paste (melting point 138°C), use 140-150°C. For high-temperature solder paste (melting point about 220°C), use 230-250°C. Preheat the soldering iron.

[0006] S200: After preheating, heat the flat spade-shaped or knife-edge soldering iron tip at both ends of the crystal oscillator for about 2 to 3 seconds. When the solder paste melts, gently push the soldering iron or use tweezers to remove the crystal oscillator from the pad.

[0007] The second method is the separation method using a hot air gun. Figure 3 As shown,

[0008] Use a hot air gun with a small nozzle, adjust the temperature to 200℃~300℃, and the wind speed to 1~2. When the temperature and wind speed are stable, hold the component with tweezers in one hand and hold the hot air gun firmly with the other hand, so that the nozzle is perpendicular to the crystal oscillator to be removed, at a distance of 1cm~3cm. Heat evenly. After the solder around the crystal oscillator melts, use tweezers to remove it in the direction perpendicular to the circuit board.

[0009] <New technical issues>

[0010] The new technical problems faced by the R&D team are:

[0011] When processing a crystal oscillator with an area less than 5mm 2 When using the crystal oscillator, the following problems were found using the two methods mentioned above:

[0012] First, the crystal oscillator area is less than 5mm 2 When using the soldering iron method or the hot air gun method, the temperature of the crystal oscillator cannot be effectively controlled, and the frequency characteristics of the crystal oscillator will be significantly affected by thermal stress, which greatly affects the subsequent crystal oscillator test.

[0013] Second, there are no protective measures for other electronic components on the PCB board. During the heating process, other components will be affected by high temperature and hot air, which may easily cause other components to fall off and be damaged.

[0014] Third, the R&D team found that the crystal oscillator area is less than 5mm 2 When using tweezers to pick up the crystal oscillator, it is very easy to touch the surrounding components, thereby causing damage to the PCB.

[0015] Based on the above newly discovered technical problems, a new solution needs to be proposed. Summary of the Invention

[0016] The object of the present invention is to address the deficiencies of the above-mentioned prior art and provide a method for heating and separating a PCB board and a surface-mount crystal oscillator.

[0017] The technical solution of this application is:

[0018] A method for heating and separating a PCB board and a surface-mount crystal oscillator, used for separating a crystal oscillator with an area S not greater than 5mm 2 The crystal oscillator includes the following steps:

[0019] Step 1: Use high-temperature insulation tape to wrap the front of the PCB (the crystal oscillator should also be wrapped in advance);

[0020] Step 2: Cut the tape just above the crystal oscillator to leave a gap;

[0021] In the third step, the back of the PCB contacts the heat dissipation module through the thermal conductive silicone sheet;

[0022] Step 4: heating;

[0023] The fourth step includes the following sub-steps:

[0024] 4.1. Determine the size of the heating nozzle of the hot air gun with auxiliary laser alignment function according to the size of the crystal oscillator;

[0025] 4.2, the heating steps are as follows:

[0026] Adjust the wind speed of the hot air gun to maintain it at 28m / s to 23m / s;

[0027] The starting temperature of the hot air gun is between 50℃ and 60℃. Place the nozzle of the hot air gun from top to bottom 1 to 2 cm away from the crystal oscillator pad to preheat the crystal oscillator for 1 minute.

[0028] Then adjust the temperature of the hot air gun at a temperature increase rate of 10°C / 30 seconds until the temperature of the hot air gun reaches the predetermined temperature;

[0029] Step 5: After the soldering tin melts, move the vacuum nozzle to the center of the crystal cover, touch the cover, vacuum, and then quickly peel off the crystal.

[0030] According to a further design, the high-temperature thermal insulation tape is a PI polyimide film coated with high-temperature silicone.

[0031] In a further design, in the second step, the area of the tape cut directly above the crystal oscillator position is less than 150% of the crystal oscillator area.

[0032] For further design, in step 4.1, the nozzle size d is determined using the following formula:

[0033] d=S+(1.4~1.6);

[0034] Wherein, d represents the nozzle diameter, in mm;

[0035] Where S represents the crystal area, in mm 2 .

[0036] Further design, in step 4.2:

[0037] For low-temperature solder paste, its melting point is 138°C, and the predetermined temperature is selected as 145°C.

[0038] For high-temperature solder paste, the melting point is 217-230°C, and the predetermined temperature is selected as 235°C.

[0039] In a further design, in step 4.2, after the temperature of the hot air gun reaches the predetermined temperature, heating is continued for 3 to 4 seconds.

[0040] Furthermore, the chip crystal oscillator is a quartz crystal oscillator or a quartz crystal resonator.

[0041] The beneficial effects of this application are:

[0042] First, when using the existing method to deal with how to separate a small-sized crystal oscillator from a PCB board, the present application found that the thermal stress of the crystal oscillator was too large, resulting in failure in subsequent testing. The aforementioned small-sized crystal oscillator refers to a crystal oscillator with an area S less than or equal to 5mm 2 The minimum area of a SMD crystal oscillator is currently 0.8mm 2 Therefore, it is more accurate to say that for small size crystal oscillators, S is 0.8mm 2 ~5mm 2 SMD crystal oscillator.

[0043] Second, in response to new technical issues, the following technical means are needed to coordinate and handle them:

[0044] 2.1, Select the appropriate nozzle of the hot air gun.

[0045] If the nozzle is too large, the heating surface is too large, and the temperature radiation area is too large, affecting the desoldering efficiency. If the nozzle is too small, the heated area is too small, which has a significant impact on the temperature of the heating surface. When the nozzle is blown onto the crystal oscillator, it is not conducive to reducing the thermal stress of the crystal oscillator. The R&D team has proposed an empirical formula: d = S + (1.4 to 1.6). In particular, d = S + 1.4 is the most suitable.

[0046] 2.2, This application proposes a new heating procedure:

[0047] Wind speed f: 28m / s~23m / s;

[0048] Starting temperature T0: 50℃~60℃;

[0049] Initial temperature preheating time t1: 60 seconds;

[0050] Temperature heating gradient V: 10°C / 30 seconds;

[0051] Predetermined temperature T1: 5℃~18℃ above the melting point of solder paste.

[0052] Predetermined temperature heating time t3: 3 to 4 seconds.

[0053] From the above, it can be seen that the heating time is: (T1-T0) / V+t1.

[0054] When determining the parameters, there are six parameters. Among them, the predetermined temperature T1 is known. t3 can be determined based on f, T0, t1, V, and T1.

[0055] Therefore, the remaining four parameters: f, T0, t1, and V can all be used as independent variables. When determining the above four parameters, if all four parameters are used as independent variables for combined testing, this parameter determination method will require a huge workload and is not feasible during R&D.

[0056] The determination method for this application is:

[0057] First, determine the wind speed.

[0058] Next, the temperature heating gradient was determined. The proposed method for heating and separating the crystal oscillator uses a heating method that increases the time and temperature in a proportional manner. By testing the effect of different temperature / time ramp rates on the crystal oscillator's frequency characteristics, we determined that 10°C / 30 seconds is the optimal method.

[0059] Again, the starting temperature T0 and the starting temperature preheating time t1 are tested as a parameter combination, and it is determined that the starting temperature T0: 50℃~60℃; the starting temperature preheating time t1: 60 seconds are appropriate.

[0060] In other words, the above five parameters are interrelated. The effect of this special design is to meet the thermal stability of small-sized crystal oscillators while also meeting the requirements of desoldering.

[0061] 2.3. The method of heating and separating the crystal oscillator proposed in this application uses vacuum adsorption to absorb the upper cover of the crystal oscillator to achieve the purpose of peeling the crystal oscillator, avoiding the situation where tweezers may touch surrounding electronic devices.

[0062] Third, the method of heating and separating the crystal oscillator proposed in this application uses high-temperature insulation tape (PI polyimide film coated with high-temperature silicone) to wrap the PCB surface to insulate and protect other electronic components on the PCB. The tape is then cut off at the heated area. Among them, the exposed area is a key parameter, and its requirement is less than 150% of the crystal oscillator area. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] The present invention will be further described in detail below with reference to the embodiments in the accompanying drawings, but this does not constitute any limitation to the present invention.

[0064] Figure 1 It is a schematic diagram of the equipment used for heating the soldering iron.

[0065] Figure 2 This is a diagram of the implementation process of the electric soldering iron heating separation method.

[0066] Figure 3 This is a diagram showing the implementation process of the hot air gun heating separation method.

[0067] Figure 4 1 is an implementation process diagram of the method of embodiment 1 (first step).

[0068] Figure 5 1 is an implementation process diagram of the method of embodiment 1 (third step).

[0069] Figure 6 This is an interface diagram of the temperature adjustment of the hot air gun in Example 1.

[0070] Figure 7 It is a flow chart of three methods (electric soldering iron heating method, hot air gun heating separation method, and the method of the present application). DETAILED DESCRIPTION

[0071] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. However, the present disclosure may be embodied in many different forms and should not be construed as limited to the embodiments described herein. It is understood that these embodiments are provided to make the present disclosure more thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art. In the drawings, the shapes and sizes of elements may be exaggerated for clarity, and the same drawings and reference numerals will be used throughout to represent the same or similar elements.

[0072] <Example 1: A method for heating and separating a highly integrated PCB and a surface-mount crystal oscillator>

[0073] A method for separating a highly integrated PCB and a surface-mount crystal oscillator by heating, suitable for separating a crystal oscillator with an area S not greater than 5mm 2 The crystal oscillator includes the following steps:

[0074] Step 1: Use high-temperature insulation tape (PI polyimide film coated with high-temperature silicone) to wrap the front of the PCB, and then use high-temperature insulation tape to tie the two to the welding table.

[0075] Step 2: Use a knife to cut the tape just above the crystal oscillator to leave a gap (slightly larger than the size of the crystal oscillator).

[0076] In the third step, the back of the PCB contacts the heat dissipation module through the thermal conductive silicone sheet.

[0077] Step 4: Heating, specifically including the following sub-steps:

[0078] 4.1 Use the hot air gun with auxiliary laser alignment function to select the size of the heating nozzle. The nozzle size is determined according to the size of the crystal oscillator (if the nozzle size is too large, the heating surface is too large, the temperature radiation area is too large, and the desoldering efficiency is affected; if the nozzle size is too small, the heating area is too small, which has a great impact on the temperature of the heating surface. When blowing to the crystal oscillator, it is not conducive to reducing the thermal stress of the crystal oscillator). The following empirical formula can be used to determine it:

[0079] d=S+(1.4~1.6).

[0080] Wherein, d represents the nozzle diameter, in mm;

[0081] Where S represents the crystal area, in mm 2 .

[0082] 4.2 Adjust the wind speed of the hot air gun: 28m / s~23m / s, adjust the temperature of the hot air gun to between 50℃~60℃, wait until the temperature and wind speed are stable, place the hot air gun nozzle from top to bottom at a distance of 1~2 cm from the crystal oscillator pad, and swing the wind gun nozzle slightly to preheat the crystal oscillator. The preheating time is 1 minute, and then adjust the temperature increase rate of the hot air gun at 10℃ / 30sec to make the crystal oscillator evenly heat up until the temperature of the hot air gun reaches the predetermined temperature.

[0083] Preset temperature description:

[0084] Currently, there are two types of solder paste commonly used on PCB boards:

[0085] For low-temperature solder paste, its melting point is 138°C, and the predetermined temperature can be selected as 145°C.

[0086] For high-temperature solder paste, the melting point is 217-230°C, and the predetermined temperature can be selected as 235°C.

[0087] Step 5: After the soldering tin on the pad melts, move the vacuum nozzle to the center of the crystal cover, touch the cover, vacuum, and then quickly peel off the crystal and place it on a thermal conductive silicone pad until it returns to room temperature (25 degrees Celsius), and then perform a 250B electrical test.

[0088] <Recognition of this Application>

[0089] First, the existing scheme does not distinguish the scope of application.

[0090] The R&D team sorted out the existing technologies and proposed the following solutions.

[0091] A design method for a PCB separated crystal oscillator comprises the following steps:

[0092] S1, measure the size of the crystal oscillator to be desoldered on the PCB;

[0093] S2, choose different welding methods according to the area of the crystal oscillator:

[0094] When the crystal oscillator area S ≥ 21mm 2 When heating, choose the electric soldering iron method;

[0095] When the crystal oscillator area S is (5mm 2 , 21mm 2 ) range, choose the hot air gun heating method;

[0096] When the crystal oscillator area S≤5mm 2 , using the heating separation method of this application.

[0097] Second, although this application also uses a hot air gun to heat the solder paste, the heating procedure is different from the traditional hot air gun heating method. The traditional hot air gun heating method is to "adjust the temperature to 200℃~300℃, and then blow directly at the solder paste"; when this method is used for small-sized crystal oscillators, the quartz crystal will fail during testing due to excessive thermal stress. This problem is more serious for S larger than 5mm. 2 , especially greater than or equal to 8mm 2 Therefore, the solution of the present application needs to break the prejudice of the traditional hot air gun heating method (direct heating).

[0098] Third, for small crystal oscillators, the hot air gun nozzle size requirements are more stringent. If the nozzle size is too large, the heating surface is too large, and the temperature radiation area is too large, affecting the desoldering efficiency; if the nozzle size is too small, the heating area is too small, which has a significant impact on the temperature of the heating surface. When blowing on the crystal oscillator, it is not conducive to reducing the thermal stress of the crystal. The R&D team proposed an empirical formula: d = S + (1.4 to 1.6). In particular, d = S + 1.4 is the most suitable.

[0099] Fourth, this application proposes a new heating procedure:

[0100] Wind speed f: 28m / s~23m / s

[0101] Starting temperature T0: 50℃~60℃;

[0102] Initial temperature preheating time t1: 60 seconds;

[0103] Temperature heating gradient V: 10°C / 30 seconds;

[0104] Predetermined temperature T1: 5℃~18℃ above the melting point of solder paste.

[0105] Predetermined temperature heating time t3: 3 to 4 seconds.

[0106] From the above, it can be seen that the heating time is: (T1-T0) / V+t1+t3.

[0107] The parameters of the above heating method are the key parameters of the present invention. The effect of this special design is to meet the thermal stability of the small-sized crystal oscillator while also meeting the requirements of desoldering.

[0108] Fifth, the method of heating to separate the crystal oscillator proposed in this application uses vacuum adsorption to absorb the upper cover of the crystal oscillator to achieve the purpose of peeling off the crystal oscillator, avoiding the situation where tweezers may touch surrounding electronic devices.

[0109] In addition, it should be noted that quartz crystals include quartz crystal resonators and quartz crystal oscillators; both types of products are used within the scope of this invention.

[0110] The above embodiments are preferred implementation modes of the present invention and are only used to facilitate the explanation of the present invention. They are not intended to limit the present invention in any form. Any person with ordinary knowledge in the technical field can, without departing from the scope of the technical features of the present invention, make partial changes or modifications to the technical contents disclosed in the present invention and make equivalent embodiments without departing from the technical features of the present invention. Such modifications still fall within the scope of the technical features of the present invention.

Claims

1. A method for heating and separating a PCB board and a surface-mount crystal oscillator, characterized in that: Used to separate the crystal oscillator area S is not greater than 5mm 2 The crystal oscillator includes the following steps: Step 1: Use high-temperature insulation tape to wrap the front of the PCB. During this process, the crystal oscillator is also wrapped. Step 2: Cut the tape just above the crystal oscillator to leave a gap; In the third step, the back of the PCB contacts the heat dissipation module through the thermal conductive silicone sheet; Step 4: heating; The fourth step includes the following sub-steps: 4.

1. Determine the size of the heating nozzle of the hot air gun with auxiliary laser alignment function according to the size of the crystal oscillator; 4.2, the heating steps are as follows: Adjust the wind speed of the hot air gun within the range of 28m / s to 23m / s; The starting temperature of the hot air gun is between 50℃ and 60℃. Place the nozzle of the hot air gun from top to bottom 1 to 2 cm away from the crystal oscillator pad to preheat the crystal oscillator for 1 minute. Then adjust the temperature of the hot air gun at a temperature increase rate of 10°C / 30 seconds until the temperature of the hot air gun reaches the predetermined temperature; Step 5: After the soldering tin melts, move the vacuum nozzle to the center of the crystal cover, touch the cover, vacuum and adsorb, and then peel off the crystal.

2. The method for heating and separating a PCB board and a surface-mount crystal oscillator according to claim 1, wherein: The high-temperature thermal insulation tape is a PI polyimide film coated with high-temperature silicone.

3. The method for heating and separating a PCB board and a surface-mount crystal oscillator according to claim 1, wherein: In the second step, the area of the tape cut directly above the crystal oscillator is less than 150% of the crystal oscillator area.

4. A method for heating and separating a PCB board and a surface-mount crystal oscillator according to any one of claims 1 to 3, characterized in that: In step 4.1, the nozzle size d is determined using the following formula: d=S+(1.4~1.6); Wherein, d represents the nozzle diameter, in mm; Where S represents the crystal area, in mm 2 .

5. A method for heating and separating a PCB board and a surface-mount crystal oscillator according to any one of claims 1 to 3, characterized in that: In step 4.2: For low-temperature solder paste, its melting point is 138°C, and the predetermined temperature is selected as 145°C; For high-temperature solder paste, the melting point is 217-230°C, and the predetermined temperature is selected as 235°C.

6. The method for heating and separating a PCB board and a surface-mount crystal oscillator according to claim 5, characterized in that: In step 4.2, after the temperature of the hot air gun reaches the predetermined temperature, continue heating for 3 to 4 seconds.

7. The method for heating and separating a PCB board and a surface-mount crystal oscillator according to claim 1, wherein: The chip crystal oscillator is a quartz crystal oscillator or a quartz crystal resonator.

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