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>> Assembly process control and skill of LCD liquid crystal display module 18th,Oct,2018
1. Assembly process:
The assembled tools are mainly hammers and wrenches, which are used to screw the frame feet. The order of the assembly operation is to first place all the tools and raw materials in an orderly manner on the workbench. Secondly, the shell is correctly placed on the workbench according to the process card description. If there is assembly tooling, put it on the tooling as required, and pay attention to the direction of the shell. Next, remove the protective film of the LCD screen, wipe the electrode clean with dust-free paper, confirm the direction, follow the process card instructions, align the frame position, load the shell to press the zebra strip, and use the special assembly tool to cover the shell and the circuit board. fixed. Be careful to twist the frame foot to 450 degrees, and do not break the board and the card so that the frame foot is in parallel contact with the PCB board. Finally, the assembled finished product is removed from the workbench, and the protective film is attached to the weekly turntable. Note that the screen should be opposite to the screen, and the board should be opposite to the board to avoid scratching. The product is assembled and inspected by the inspection personnel, and the assembly is unqualified.
2. Assembly method:
The purpose of the assembly is to make the screen and the electrodes of the circuit board correspond one-to-one, so that the electrical performance is matched. However, since the screen is not in direct contact with the circuit board, and the conductive strip is used as the medium, the screen and the board cannot be visually matched, so that the respective corresponding electrodes cannot correspond to each other, resulting in a misalignment phenomenon. The electrode connection corresponding to the screen and the circuit board in the assembly process is called the alignment. In the assembly, the corresponding screen and the board are realized by the alignment of the screen and the board and the alignment of the shell and the board. . The shell acts as an intermediate medium and serves as a corresponding standard for the screen and the shell, which plays a large role in the alignment. The alignment method mainly has edge alignment, pinhole alignment and intermediate alignment.
(1) Side alignment:
Edge alignment is the alignment standard of the liquid crystal screen and the electrodes on the circuit board by means of a short side of the frame,
To achieve assembly alignment, edge alignment actually refers to the alignment of the screen and the shell. Since the edge alignment refers to the alignment of the screen and the shell, there are some alignment methods for the different situations of the screen and the shell. For the shell, since the shell has many kinds of conditions according to different design requirements, such as a symmetrical shell, a notched side without a notch, the direction of the shell foot, etc., these can be used as the shell in the side alignment benchmark, in the description It can be called the edge edge alignment and the non-open edge alignment, the edge alignment, and the like. The opposite side of the screen has only the open side and the closed side, so it is often called the opposite side of the open side and the non-open side, and when the two are combined, the combination of the two is used, such as: The sealing edge of the screen is on the opening side of the shell, the non-sealing edge of the screen is on the non-opening side of the shell, and the opening side of the screen is on the side of the shell. According to the above-mentioned some screen and alignment methods, combined with the alignment mode of the circuit board and the shell, for example, one shell foot or two shell feet of the shell are used as the alignment reference. This completes the assembly with the edge alignment as the alignment side. This assembly method is suitable for modules with wide electrodes.
(2) Pinhole alignment:
For the assembly of some screens with narrow electrodes and circuit boards, such as modules with an electrode width of 0.35mm and 0.5mm,
There is a finer alignment method, which reduces the error between the screen and the circuit board in assembling the opposite electrodes, improves the yield and reduces the consumption, so the pinhole alignment method is adopted. The pinhole alignment method is a fine calculation, and two alignment holes are used on the shell as a reference for the screen alignment. When assembling, the sealing edge or the non-sealing edge of the screen is tangentially inserted into the outer edge of the two alignment holes, and when the circuit board is placed, the two assembly pinholes on the circuit board are aligned to make the shell The positioning hole is concentric with the positioning hole on the circuit board. At this time, the electrodes on the line have exactly one-to-one correspondence with the on-screen electrodes, thereby achieving assembly alignment.
(3) Intermediate alignment:
In addition to the alignment of the pinholes, the alignment method is called the intermediate alignment. Design the shell to be symmetrical during design
shell. The liquid crystal screen is placed on the basis of the long side of the shell or the gap on the short side, so that the screen is in the middle of the whole shell, so that the long side bisector of the screen coincides with the long side bisector of the shell, and when the circuit board is placed, The two outermost assembly holes on the same side of the circuit board or the positioning holes on the circuit board cooperate with the positioning small protrusions on the casing to form a positioning reference with the casing, thereby achieving assembly alignment.
1. LCM assembly skills:
In the long-term production practice, as the number of assembly increases, the accumulation of experience, you can slowly master a lot of assembly.
Skills (assembly skills are about assembly skills).
(1) Improve the yield:
In module assembly production, the primary yield is an important factor in assessing production efficiency and the technical level of an assembler.
parameter. A high yield rate can improve production efficiency, ensure work completion time, reduce necessary labor time, and reduce labor costs. In addition, the reliability of the module can be guaranteed.
(2) Reduce waste and reduce costs:
If a module is assembled multiple times, it may increase the cost of its materials. Such as scratches on the screen, scratches on the shell, paint falling off,
The most important thing is to deform the shell foot and reduce its due stress, which affects the reliability of the module. If you have good assembly skills, guarantee the yield of the module, and reduce the number of assembly, you can reduce the cost of the screen and the shell.
(3) Eliminate the difficulty of alignment due to unqualified raw materials:
In production, due to the failure of the shell or circuit board, the alignment difficulties can occur, but if there is a good alignment
Skills, some of the difficulties caused by raw materials can be solved.
2. Experience and principle:
Skills are techniques that accumulate experience in production and then refine it. The assembly technique comes from production.
It is a cumulative summary of experience, so it is necessary to have certain experience, and it is impossible to have good skills without experience.
The assembly principle is simple in that the electrodes of the liquid crystal panel are in one-to-one correspondence with the corresponding control electrodes on the circuit board. So experienced
On the basis of the principle, the assembly skills are fully utilized to promote production. Assembly techniques are extremely useful in overcoming the alignment difficulties caused by raw materials. Due to the unqualified raw materials such as shells, screens and circuit boards, the alignment mode is invalid and cannot be assembled according to the original procedure, ie the original process documentation, which means that the assembly at this time is blind. For the difficulties of alignment caused by these reasons, two main techniques are mainly used to solve them. One is to re-find the alignment benchmark; the other is to visually check the alignment. There is also the use of tooling alignment.
(1) Re-finding the alignment benchmark
Sometimes the alignment reference between the screen and the shell or the shell and the board fails due to the raw material or the original process document due to the accumulation of tolerances. In the production, it is necessary to find the alignment reference again to achieve the positioning of the assembly. Before re-finding the alignment benchmark, we must analyze the cause of the failure of the alignment benchmark and then solve the problem, so as to achieve targeted production and smooth production. The main failures of the alignment reference are the three basic raw materials for the shell, screen and circuit board.
The alignment failure caused by the shell is the most common, mainly manifested in: the positive edge of the shell is too large, and the width of one electrode has exceeded the width of one electrode, which makes the edge alignment invalid. The pinhole is not in the correct position and the pinhole alignment cannot be performed. The wide side is too long, causing the screen to produce a certain angle, causing the electrodes to be misaligned. The long side of the shell is too long, resulting in an increase in the positive tolerance. Since the electrode width of the screen and the board is constant, if the edge alignment is used, the screen electrode is displaced more than the design. When the displacement exceeds one electrode, if the assembly is performed by the edge alignment, the screen and the plate electrodes are inevitably misaligned, resulting in assembly failure. At this time, it is necessary to re-determine its alignment benchmark. There are two references for the assembly alignment, one is the alignment of the screen and the shell; the other is the alignment of the shell and the board. Since the alignment reference between the shell and the circuit board is often based on the shell foot for the alignment of the edge, the edge alignment can still be used to make the screen and the side of the shell close; however, the pair of the shell and the circuit board is changed. Bit benchmark, then the choice of shell feet should be determined according to the experiment.
If the alignment difficulty is caused by the pinhole of the shell, because the alignment of the screen and the shell fails, the same side alignment needs to change the alignment of the shell and the circuit board, and the circuit board is no longer The pinholes of the shell are the same axis, and the tolerance of the circuit board relative to the shell is positive, and the same movement is performed to compensate for the gap between the electrodes caused by the tolerance to achieve the alignment.
In general, looking for a new alignment benchmark is to be found in practice and in actual assembly. Sometimes the tolerance is too large, and the electrode spacing is small. It is extremely difficult to find the alignment benchmark. Some experienced people. Make full use of the assembly principle to overcome the error and assemble it. This is the visual alignment.
(4) Visual alignment:
The principle of assembly is to make the electrodes of the liquid crystal screen correspond to the corresponding control electrodes on the circuit board, which is the assembly principle.
It is also the basis for visual alignment. After determining the corresponding relationship between the screen and the circuit board, the screen is placed in the shell, and then the side of the circuit board having the electrode is placed on the side of the shell to be in close contact with the shell, so that the electrode on the circuit board and the screen electrode are in one-to-one correspondence. Observe the position of the PCB board and the shell, then put the conductive strip, and then place the circuit board for assembly.
(5) Using the tooling alignment:
When assembling, some alignment methods are not convenient to operate, such as pinhole alignment, to make the circuit board and the shell needle
The hole correspondence is not to look at the eye to make the pinholes of the two correspond to the same axis. In production, the accumulation of people's experience has slowly got an idea, can you achieve the alignment by means of auxiliary tools. So I developed some kind of cheap and practical tooling - assembly tooling. It is used according to the principle of alignment to improve assembly efficiency, improve yield and reduce waste.
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