HDMI production processing and its affection

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In this article, we will discuss the cabling process’ affection on the performance


Cabling’s processing affection on the performance of HDMI:

Foam processing: take 50%,most important part in cabling use dB to shows the signals attenuation

Signal attenuation is closely related to impedance. Impedance matching and impedance stability are of great significance to attenuation. As can be seen from the above figure, it is very important to control the foaming degree to ensure stable impedance during the foaming process of the core wire.Now the new foaming machine can automatically control the temperature, so it can ensure the foaming stability throughout the whole process, while the old-fashioned machine is controlled manually, and the value of the static capacitance is adjusted every minute.

So, are there any employees who will help you keep an eye on the static capacitance to adjust the foaming degree in minutes? Obviously it is unrealistic. Go to the toilet and drink a glass of water and leave. Even if not, the night shift is too tired and doze off, the core wire control is not in place, and the core wire has a great impact on performance. This process cannot guarantee stability. , No matter how hard the subsequent process is, it will not help. In addition, the surface of the conductor is oxidized because of the skin effect during high-frequency transmission. Signals are transmitted through the surface of the conductor. If the conductive surface is oxidized, it means that the highway is full of stones, and the car must not drive fast. There is also the core eccentric problem, which will affect the capacitance distribution and produce the problem of electromagnetic field imbalance and seriously affect the signal. A few of this problem is because the mass production is not adjusted properly, and most of the problems are because the foaming mold is worn out and it is difficult to adjust the eccentricity. Open line.

Twisting process: the impact accounts for 5%

For twisting, ensure that the physical lengths of the two core wires are the same. In order to ensure the delay difference, that is, the signal can go from this end to the other end The transmission distance should be infinitely close.

The time for the signal to travel from end A to end B is called delay difference

The time it takes for the signal of a core wire in 1P to go from A to B

The time it takes for the signal of the other core wire in 1P to go from A to B

Internal delay difference (≤112ns, Cat2 standard) 1s=10^9ns,1 nanosecond is equal to one billionth of a second

At present, most factories can use the power pay-off rack to automatically control the pay-off force of the two core wires to ensure that the physical lengths of the two core wires are the same.


foil shield wrap processing: occupy 20%

The wrapping paper cannot be too tight or too loose. Too loose wrapping may cause signal crosstalk and reflection due to slitting of the aluminum foil, which will seriously affect signal attenuation. Too tight the package will cause the core wire to deform and cause serious electromagnetic field deformation, signal reflection interference, and also seriously affect signal attenuation. At present, a small number of factories use new machines to wrap paper. The new machines can automatically track the tightness of the aluminum foil to ensure that the strength of the aluminum foil for all signal pairs is the same, and the wrapping will not be too loose or too tight. However, most factories use old equipment, and the strength of wrapping paper is entirely based on the experience of the employees. Once a novice employee is used to operate it, quality problems are likely to occur.

Wrap (roll wrap): Aluminium foil wraps (rolls) the core wire in 360 degrees, the core wire does not rotate

Wrap processing, occupy 20%

Towing strap (oblique strap): The core wire rotates at high speed, and the aluminum foil is brought in by the rotating core wire

In addition, many factories currently use horizontal twisting and wrapping machines to complete the twisting and wrapping processes together. Because the horizontal twisting machine adopts the form of towing and wrapping, the production capacity is 2-3 times of the original (twisting and wrapping aluminum foil) process. However, the quality is low, and the aluminum foil is easy to loosen. There is also a 405 synchronous machine that also drags the aluminum foil while twisting it. This kind of machine is only suitable for ground wire insulation without pressing, suitable for wrapping aluminum foil + hot melt Mylar method

Total twisting (collection twisting) process: accounted for 5%

Total twisting (collection twisting) process: accounted for 5% Generally, the influence of twisting is not there. Pay attention to the wire mold that it should not be too small,which would squeeze the core wire braiding and extrusion process: 5% The two processes have little impact, so be careful not to crush the core wire. The sheath is half-squeezed to reduce the pressure on the inner core wire.

Process design: 15%

For example, the foaming degree of the core wire is generally designed to be around 40%, but some factories design around 50% of the limit, although the foaming degree is high, the dielectric constant becomes small, theoretically, the attenuation will be better, but we ignore a problem that the PE physics after foaming the strength and other properties deteriorate and the core wire becomes softer, and the higher the foaming degree, the softer the insulating part, which is susceptible to compression deformation during subsequent processing and affects the signal. In addition, the impedance value specification requires 100±10 ohms, and the design is about 100 ohms. Too high or too low impedance will affect signal transmission, TDR test is difficult, EMI test is not good.

1.3The influence of processing procedure on performance: When opening the aluminum foil, try not to cut the foam core wire. The length of the opening is controlled within 15mm. When opening the aluminum foil, be careful not to make the aluminum foil too loose. The wires required by EMI should be 100% girth welded shielding

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