TWI387415B - Method of reducing warpage of circuit board assembly - Google Patents

Description

Method for reducing board assembly warpage

The present invention relates to a method of board assembly, and more particularly to a method of reducing board assembly warpage.

In the existing circuit board assembly method, the component manufacturing process on the printed circuit board (PCB) can be mainly divided into surface mount technology (SMT) and die bonding technology (die bonding). Kind.

Referring to FIG. 1 , a wafer in a Flip Chip or Ball Grid Array configuration is used as an example. The surface adhesion technique is to bond a wafer 12 with a plurality of solders 11 according to the solder. The position of 11 is placed on a plurality of metal contacts 131 of a printed circuit board 13 corresponding to the circuit to be connected, wherein the metal contacts 131 are first coated with a solder paste or a flux according to the process requirements. After the materials are then baked at a high temperature in the reflow furnace, the solders 11 are respectively melted between the wafer 12 and the metal contacts 131. After cooling, the solders 11 are solidified to fix the wafers 12 to the wafers 12 The printed circuit board 13 is electrically connected to the corresponding metal contacts 131, and finally cooled for subsequent processing.

Referring to Figures 2 and 3, in the wafer bonding technique, for example, a printer head wafer (light emitting diode array or inkjet wafer) having a length of about 20 cm (i.e., the size of a general A4 file) is adhered. Silver paste (not shown) is first coated on a printed circuit board 15, and then the plurality of wafers 14 are placed on the silver paste, and then placed in an oven for a period of high temperature baking to cure the silver paste at a high temperature. Thereafter, the wafers 14 are adhered to the printed circuit board 15, and finally the product obtained after cooling can be subjected to a subsequent wire bonding process.

However, in the foregoing two technologies, since the copper foil material of the printed circuit board is mainly a material that absorbs heat and stores heat energy, during the cooling process, the printed circuit board is on the side where the wafer is not mounted, since the copper foil is directly exposed to the air. The surface area is large, so the surface heat dissipation effect is better, so that the cooling and shrinking speed of the side is faster, and the heat of the printed circuit board on the side where the wafer is mounted must be transferred through the solder and the surface of the wafer, so that the heat dissipation effect is poor, so that The cooling shrinkage of this side is slower, taking the wafer bonding technique as an example, which causes the printed circuit board 15 to warp against a reference line X (see Fig. 3).

Therefore, before the subsequent process processing, it is often necessary to apply an external force or a fixture to make the cooled printed circuit board flat, so as to facilitate subsequent processing, but this method is liable to cause damage to the wafer or solder joint. Taking a light-emitting diode array (LED Array) as an example, the warped portion may cause errors in assembly or measurement of the optical component during optical alignment or measurement, which seriously affects product quality. The increase in production costs also reduces the yield of the product.

Accordingly, it is an object of the present invention to provide a method for reducing warpage of board assembly.

Thus, the method of the present invention for reducing board assembly warpage comprises the following steps:

(A) providing a temperature measuring module and a warping measuring module for measuring a temperature and warpage data of a circuit board when the temperature is lowered, and recording in a recording module;

(B) calculating the temperature and warpage data to produce a temperature control command that causes the expected warpage of the board to be below a target warpage value; and

(C) using a control module to drive the two convection modules on the outside of the opposite surfaces of the circuit board to operate with the temperature control command such that the warpage of the circuit board is below the target warpage value.

The effect of the invention is that the convection module is used to control the shrinkage rate of the opposite surface of the circuit board during cooling to reduce the occurrence of warpage.

The above and other technical contents, features and advantages of the present invention will be apparent from the following detailed description of the preferred embodiments.

Referring to Figures 4, 5 and 6, the preferred embodiment of the method of the present invention for reducing board assembly warpage comprises the following steps S20-S26.

In step S20, first, the to-be-processed unit 3, which is still in a high temperature state, is taken out from the previous stage process, and the to-be-processed unit 3 includes a plurality of wafers 31 that have been bonded to be cooled and an elongated circuit board 32. In this embodiment, the to-be-processed unit 3 is a circuit of a printer head, and each of the twenty-six LED arrays 30 and the wafer 31 corresponding to the LED arrays 30 are driven by a wafer bonding technique. (Driver IC) is fixed on the circuit board 32 with silver glue (see Fig. 7), and taken out after baking in the oven. It is worth mentioning that the to-be-processed unit 3 can also be a wafer and a circuit board bonded by surface adhesion technology, and taken out after baking in a reflow oven (not shown).

The circuit board 32 is connected to a measuring unit 4, and the measuring unit 4 includes a temperature measuring module 41 and a warping measuring module 42 respectively adhered to the surface of the circuit board 32, and a The temperature measuring module 41 and the recording module 43 of the warpage measuring module 42 are electrically connected.

Referring to FIGS. 4, 5, and 7, the temperature measuring module 41 has ten temperature sensors 411 attached to the two surfaces of the circuit board 32 to respectively measure the temperature, and the warpage measuring module 42 has ten The circuit board 32 is respectively disposed corresponding to the temperature sensor 411 to measure the warpage size of the circuit board 32, and each surface of the circuit board 32 is mounted at approximately equal intervals along the long direction. Five temperature sensors 411 and five displacement sensors 421. In the present embodiment, the temperature sensors 411 are respectively thermocouples, but may also be non-contact infrared sensors, and the displacement sensors 421 are respectively strain gauges.

4, 5, and 6, in step S21, the temperature sensors 411 of the temperature measurement module 41 and the displacement sensors 421 of the warpage measurement module 42 are respectively used. The temperature and warpage data of the circuit board 32 in the air from the high temperature to the room temperature and the corresponding time data are measured and recorded in the recording module 43. This step S21 is then repeated until the cooling is completed, at which time the circuit board 32 is warped with respect to a reference line L (see Fig. 6), and then proceeds to step S22.

In this step S22, the heater unit 3 is reheated to a temperature before cooling by a heater (not shown).

Next, in step S23, a simulation calculation is performed on the temperature and warpage data obtained before cooling, and the simulation calculation is used to calculate that the circuit board 32 is adjacent to one side of the wafer 31 and the opposite wafer. When one side of 31 can have the same cooling shrinkage rate, the temperature control commands required for the two surfaces respectively cause the expected warpage of the board 32 to be lower than a target warpage value. It is to be noted that the temperature control command has two modes for the two surfaces of the circuit board 32, respectively. In this embodiment, the temperature control command is a sequence that changes over time, and is a control command written by a program.

Referring to FIGS. 4 and 8, step S24 is followed to move the unit to be processed 3 to a cooling unit 5. At this time, the measuring unit 4 is still connected to the circuit board 32 (not shown). 5 includes a control module 51, and two convection modules 52 electrically connected to the control module 51 and respectively located outside the opposite surfaces of the circuit board 32. In this embodiment, the convection modules 52 are respectively fans that can adjust the wind speed.

At this time, the control module 51 is used to drive the convection modules 52 to operate in two modes of the temperature control command for cooling operation, so that the opposite surfaces of the circuit board 32 can be respectively controlled. The same temperature, so that the circuit board 32 can have the same cooling shrinkage rate on one side of the wafer 31 and on the opposite side of the wafer 31, so that the warpage of the circuit board 32 is lower than the target warp. Curvature. It should be noted that during the cooling process, the temperature and warpage data of the product and the corresponding time data are recorded at the same time.

Next, in step S25, the measured warpage size is compared with the simulation calculation result. If the warpage size of the circuit board 32 is lower than or equal to the target warpage value, step S26 is performed, if not, Then, the process returns to step S21 and the simulation calculation correction is performed at step S23, and the verification is repeated until the warpage size of the circuit board 32 is lower than or equal to the target warpage value.

In step S26, it is similar to the step S24, the difference is that the to-be-processed unit 3 uses the new to-be-processed unit 3, and the measuring unit 4 does not need to be connected to the circuit board 32 at this time.

Thus, after the step S20 to the step S25 are sequentially performed, the step S26 can be repeatedly performed until the to-be-processed unit 3 is completely processed.

Since the present invention utilizes the temperature variation of the two surfaces of the circuit board 32 to control the expected warpage of the circuit board 32 to be lower than the target warpage value, the same temperature control command can be applied to the same type of the unit to be processed. 3. Further, other steps can be omitted and only a large amount of batch processing is performed in the step S26. Therefore, the warpage size can be further reduced to improve the yield compared to the conventional circuit board assembly method.

In summary, by applying the convection modules 52, the temperature of the two surfaces of the circuit board 32 can be separately controlled, and the shrinkage rate of the two surfaces is maintained during cooling, so that the circuit board 32 is cooled to reduce warpage. The occurrence of the phenomenon makes it possible to achieve the object of the present invention.

The above is only the preferred embodiment of the present invention, and the scope of the invention is not limited thereto, that is, the simple equivalent changes and modifications made by the scope of the invention and the description of the invention are All remain within the scope of the invention patent.

3. . . Pending unit

31. . . Wafer

32. . . Circuit board

4. . . Measuring unit

41. . . Temperature measurement module

411. . . Temperature sensor

42. . . Warpage measurement module

421. . . Displacement sensor

43. . . Recording module

5. . . Cooling unit

51. . . Control module

52. . . Convection module

1 is a schematic view of a conventional surface mount technology in which a wafer is mounted on a printed circuit board;

2 is a plan view of a conventional wafer bonding technology in which a wafer is mounted on the printed circuit board;

3 is a schematic view of the printed circuit board after cooling in the conventional wafer bonding technology;

4 is a flow chart of a preferred embodiment of the method for reducing board assembly warpage of the present invention;

Figure 5 is a schematic view of the preferred embodiment in the measurement phase and prior to cooling;

Figure 6 is a schematic view of the preferred embodiment in the measurement phase and after cooling;

Figure 7 is a schematic diagram of the system of the preferred embodiment in the measurement phase; and

Figure 8 is a schematic illustration of the system of the preferred embodiment in a cooling stage.

3. . . Pending unit

31. . . Wafer

32. . . Circuit board

5. . . Cooling unit

51. . . Control module

52. . . Convection module

Claims (4)

A method for reducing warpage of circuit board assembly includes the following steps: (A) providing a temperature measurement module and a warpage measurement module to measure a temperature and warpage data of a circuit board when the temperature is lowered. And recording in a recording module; (B) calculating the temperature and warpage data to generate a temperature control command that causes the expected warpage of the board to be lower than a target warpage value; and (C) applying a control The module operates to drive the two convection modules located on opposite sides of the opposite surfaces of the circuit board with the temperature control command such that the warpage of the circuit board is lower than the target warpage value. According to the method for reducing the warpage of the board assembly according to the first aspect of the patent application, after the step (A) and the step (B) are sequentially performed, the step (C) is repeatedly performed. The method for reducing warpage of circuit board assembly according to the second aspect of the patent application, wherein the temperature measuring module of the step (A) has a plurality of temperature sensors for measuring different positions of the circuit board, the warping The measurement module has a plurality of displacement sensors corresponding to the temperature sensor settings to measure the warpage of the circuit board. According to the method for reducing board assembly warpage described in claim 3, the temperature control command has two modes for driving the convection modules respectively.