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What is COF? Its principle design

Author:admin Time:2017-07-03

COF, its English name "chip-on-flex", is a newly developed technology of LCD module. It has a great breakthrough in product size, weight and high integration. Because the flexible circuit board is thinner and lighter than the solid PCB, the COF module is small in size, light in weight, and fast in design and production.
First, the COF module structure
In order to form a complete LCD module, the FPC (flexible, printed, circuit) requires several external capacitors to be welded, which shall be accomplished by special equipment and fixtures through the SMT reflow equipment. The main modules of the COF module are: LCD glass board, FPC, drive IC, connect FPC to LCD ACF, connect chip with FPC ACF, chip capacitor and resistor.
Two, COF module features
1, because the components are on the FPC, so the COF module is small and light weight. The following is a comparison of various types of modules.
2, due to the use of FPC, this module can be designed according to their soft ligament width, and did not like the design of the tab module by the tab size limit, such as the impact of tab module is often affected by the soft ligament width, in the use of LED backlight has received very limited.
3, because some components can be directly attached to the FPC, so that it can reduce the components on the motherboard.
Three, drive chip and LCD connection principle
ACF (ACF) is a kind of thermosetting resin, which are distributed conductive ball, when the ball on the gold electrode and the wire end is squeezed when conducting, type cog module is connected with this method, it has the advantage of processing time is very short.
And another way, another COF help paste technology is Au-Sn eutectic, the tin film is covered on the FPC chip on the electrode by heating, and the IC bump electrode with gold eutectic alloy become together, then the gap between the chip and the tin film fill out the filler, this method there is a potential advantage in fine pitch future, this is the ACF mode can not be solved, but is still not a reality, there are many shortcomings in the production, for example, need a longer exposure time, temperature, and necessary filler, used this technique in the past production of tab.
All LCD drives with gold electrodes can be made into COF using this technique.
Four, COF connection
COF due to the contact surface of the gold, but also behind the insulation of the PI, which makes COF can be made into any available means, such as socket with FPC contact, strengthen the pulling type and FPC can be used with double contact surfaces can be welded to the PCB average, in addition there is a hollow electrode contact, when in use can also be directly welded on the PCB, but in this way by the impact of raw materials, domestic manufacturers generally do not become the.
Since the integrated micro semiconductor material (drive + character rom+ active device) is directly inverted soldered to the COF, it can be subjected to reflow soldering of the SMT process, so that some capacitors and resistors can be attached to the cof.
COG device
The picture shows the Europa League COG equipment
Five, design methods
1, according to the actual requirements of chip data and modules, draw the schematic diagram of cof.
2, draw COF outline drawing
According to the module of the overall design requirements draw the outline of COF, then contact electrode and LCD, under normal circumstances, driving the com number and +seg number are used, each with one or two on the electrode, is the total number of electrodes n, if the electrode spacing is p, the outside two electrode distance is l1=p1 (x n1-1). With the LCD part of the contact width is generally W1 = l1+2mm, COF module and CPU control interface, the interface is used to draw the way with strengthened pull type, if the number of electrodes is N2, spacing is P2, the two outside electrode spacing is l2=p2 * (n2-1), the width of the w2=p2 interface * (n2+1) + 0.1mm, if using double-sided contact type, electrode spacing is relatively large, in general, not less than 0.6mm, 0.8mm is generally preferred spacing.
3, draw the chip pad, pad graph chip is very important, the general chip data have each pad position table according to the position of the pad surface, a draw, future bonding chip, chip bump and pad to FPC graphics correspondence.
4, placing the whole module components, in accordance with the requirements, the chip pad, pad map of other components of a reasonable place to map, in the laying process, should follow the following principles: one is to ensure that the line can go, especially IC and LCD part of the top of the driving element is two more lines; put reasonable, to avoid double line.
5, walk the line, this is a key part of the design, not only to the principle diagram of the line to go through, but also to ensure good display effect, you need to walk the line should be reasonable, go near the line can be a little thin, long distance line should be a little rough, such as driving the SEG line in general, in between, the journey is short, can be a little thin, while driving the com line on both sides, will be thicker. In addition, the power line and the control line have to go a little bit thicker, and even can use two wire belts to lift a thread. Below is the standard for COF's internal lead and external lead:
6. Coating requirements
7, check the design, according to customer requirements and the use of methods, check whether the design reached customer goals.
Six, design examples
The original customer use of an old TCP, because the old TCP production, their host membrane and are unable to change, according to the actual situation, we are prepared to use Samsung's s6b0719 chip, but a lot of s6b0719 TCP, can meet the customer requirements, COG chip then we use s6b0719 to open a co

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