Sources of Catastrophic Error
The first source of catastrophic error in a cable is the existence of unintentional opens or shorts in the structure. These can arise due to failures at the myriad of soldering points in the cable. Short circuits can easily occur at these solder joints with inaccurate soldering causing bridges between wires, given that much of the soldering in these cables is still done by hand. The solder joints can also be poorly formed and can break in the follow-on processing, leading to open circuits.
Another area of such defect is the existence of insulation pinholes in the individual conductors, which will cause destructive conductive paths.
Figure 4a: Solder Defect in Cable Connector
Figure 4 shows an example of a solder defect in a cable. In this example, the wires from an HDMI cable are connected to a PCB on an HDMI connector. Looking at top photo, it is seen that the solder on some of the landing pads is poor. Looking closer at middle and bottom photos, the solder is seen to create a short circuit between adjacent wires on the PCB.
Figure 4b and c: Solder Defect in Cable Connector
In addition to the catastrophic short/open defects that can occur with every cable, high-speed cables have a further constraint in that they are subject to stringent signal loss requirements. All copper cables have limited bandwidth — while the low frequency signal’s energy will be passed unaltered, the high frequency energy in the signal will be attenuated. The magnitude of this attenuation constitutes a pass/fail requirement in high-speed cables. The logic behind this is that beyond a certain level of attenuation high speed signal integrity will be lost in the cable. The variation in attenuation in cables comes from two sources.
NEXT: Sources of Signal Attenuation
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