Bend Flex and Twist Requirements

It is important to consider the bending and flexing properties of high frequency Micro-coaxial and Twinax cable assemblies, when designed into new smaller, compact portable electronics. Both Micro-coaxial and Twinax cables are specified for Minimum Bend Radius, a parameter that determines how tightly these cables can be bent repeatedly with out being damaged and still ensuring high signal integrity. Minimum bend radius is typically measured in millimeters. A typical use case of Micro-coaxial cables is to provide the  connectivity between the display and motherboard in systems using hinge. Micro-coaxial cables are also specified for twisting, a parameter that allows the rotational movement of cable along the Y axis and is typically measured in degrees. 
When it comes to Micro-coaxial Cables, the recommended minimum bending radius of cable is “6 times Wire O.D" but the actual specification depends on customer's selected coaxial cable.

Bend Flex and Twist Rqmnts_3

Bend Flex and Twist Rqmnts_1

Bend Flex and Twist Rqmnts_2

Microcoax cables are tested for bending and flexing performance by using a test fixture which allows to bend the cables at +/-90 degrees under load conditions. Idea is to stress the cables with multiple bending/ flexing cycles and measure the S-parameters of cable after a certain number of cycles. The S-parametric performance after the completion of bending/ flexing cycles is compared with the S-parametric performance of initial samples before the tests. The cables are also inspected at the end of test cycles for any mechanical failures including wire breaks. Bending/ Flexing performance of Micro-coaxial cables is listed in the Table 1. below :

Bending radius/group
Test sample ID (AWG#44) 
(times)
Avg.
 
1
2
3
4
5
1mm / No.1
3.5K
4.2K
4.2K
3.4K
4.3K
3.9K
2mm / No.2
25K
30K
26K
30K
28K
28K
5mm / No.3
400K
600K
500K
600K
450K
500K

Table 1. Bend/ Flex Performance of Coax Cable

 

Similarly, Micro-coaxial cables are tested for twisting performance by using a test fixture which allows to rotate/ twist the cables along Z-axis by +/-180 degrees under load conditions. Idea is to stress the cables with multiple twist cycles and measure the S-parameters of cable after a certain number of cycles. The S-parametric performance after the completion of Twisting cycles is compared with the S-parametric performance of initial samples before the tests. The cables are also inspected at the end of test cycles for any mechanical failures including wire breaks. Twist cycle performance of Micro-coaxial cables is listed in the Table 2. below : 

Test condition
Test sample ID (AWG#44)   (times)
Average
1
2
3
4
5
+/- 180 deg.
>900K
>900K
>900K
>900K
>900K
>900K

Table 2. Twisting Performance of Coax Cable

 

When it comes to Twinax Cables, the construction of cable restricts the bending and flexing in the direction of its height only as shown below. Since the two conductors are placed side by side separated by solid dielectric in the cable, bending side ways can damage the cable physically also impacting the electrical performance and the signal integrity of data.  
As a rule of thumb, the Minimum Bend radius for Twinax cables is specified as 10 times the height of cable as shown below. 

 

 

Minimum cable bending R :
10 times Height

 

 

 

Bending Not Allowed 

Qstns_7-4

  Minimum cable bending R : 
10 times Height

 

 

Bending Not Allowed 

 

                                                Width

Qstns_7-5

                                              ↑ Jacket

 

 

Height

 

Back to Micro-Coaxial/Twinax Connectors