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What is PCB CTI?

Concerns about electrical safety are not isolated to electrical boxes or other equipment of high voltage, distribution lines, and transmission, caps, and transformers. PCBA, which includes virtually all systems, appliances, and devices that we make use of, can be dangerous if there is an occurrence of contingency where there is an exposure of users or personnel to extreme current level. This is more likely to happen for industrial boards of which high current printed circuit board tips and guidelines for designing should be adhered to.

What Does The Comparative Tracking Index Mean?

The comparative tracking index is similar to the high voltage arc tracking rate (HVTR), it evaluates or measures the capability of a Printed circuit board surface to withstand tracking. In this case, tracking refers to faulty insulation materials that exist between conductive surface elements like traces and pads.

A printed circuit board is utilized to offer mechanical help and to interface electrical elements electronically by utilizing conductive pathways, the signal follows or tracks engraved from copper sheets covered onto a non-favorable substrate. Comparative tracking index is the ability to which Printed circuit board materials that have the insulating capability of resisting unneeded current to have flowing access on the board between traces.

It is the measurement of the capability that the Printed circuit board underlying support has to confront any failure or crack-down between double tracks on the outside layer of the printed circuit board materials. It is made use of in assessing the level of resistance of the printed circuit board base material and assists in calculating the high-voltage segregated or in solitude values between the tracks.

PCB CTI Value

PCB cti value

The comparative tracking index value depicts the resistance of the printed circuit board materials against ecological influences like moisture and dirt. This is well explained in terms of when the value is higher, then the higher the material is, the more resistant. FR4 CTI has a default comparative tracking index of 175 and which may increase to about 600 unique materials.

The worth of comparative tracking list is learned with the utilization of standard test techniques Tracking resistance is the refusal and opposition against the current flow put forward by the Printed circuit board. The rising in the digit of elements placed on the printed circuit board increases its general packing density; this contributes to little trace spacing. Hence, the CTI value in the printed circuit board base material is very essential.

These values contribute to the reduction in the general printed circuit board resistance to tracking. These values provide an evaluation for loss of electricity most especially as a result of faulty or breakdown insulation or short-circuit as trace spacing gets reduced as a result of the elevated number of elements. On the basis of the standard set by the IEC, the smaller comparative tracing index grade substratum provides great resistance to electrical breakdown.

A comparative tracking index is a number that is critical while picking a printed circuit board material. The range of a normal FR-4 CTI is from 175 to 225V.

The increment in the packing density of elements on the printed circuit boards increases smaller conductor track spacing. Thus, the PCB CTI value in the base material data sheets becomes increasingly more essential. This is the scale for resistance tracking.

Comparative Tracking Record

Comparative tracking record is the technique for estimating a material as an electrical encasing and is given as the voltage at which while going through a trial of normalization, the outside of materials separates. Comparative tracking index numbers for products are published by the Printed circuit board laminate manufacturers.

Here comparative tracking index is an item of good quality which is applicable to Copper Clad laminate which is mostly used in domestic electronics or electrical apparatus with a voltage at a high rate (110V, 220V). It is a dummy situation that the Printed circuit board in its work environment suffers from pollution, which leads to short-circuiting or leakage at the track gap of the Printed circuit board surface, of which charring and heat-releasing is the companion.

The method of experimentation is that continuous 50 drops of 0.1% ammonium chloride solution are released along with the dual points on the Printed circuit board surface, half a minute per drop, switching on high voltage AC current to do the testing.

The first instance is trying 300V to generate a 1A current. On the outside layer, there is a solution with ammonium chloride, so after switching on the current, resistance will be produced which also generates heat, after which the solution evaporates slowly. The second drop is on and goes till 50 drops to observe if there is leakage with the Printed circuit board or not. Once there is a creepage of 0.1A and goes above 0.5 seconds, it’s said to have failed.

There are high PCB CTI (increased CTI 600 pcb material backed by aluminum, CTI 300, and CTI 600v PCB) which works in such a difficult environment of humidity, filth, and high voltage.

It must be stated that the most important aim of all standards for electrical safety is preventing any danger caused by shock. On that basis, the creepage and clearance allowance among its conductors that are prone to the voltage that is hazardous can be the lowest that guarantees the circuit will be functioning and not deteriorating.

IEC-60950-1 highlighted five accelerating levels of compulsory insulation that are related to the physical location of a circuit that is relative to contact by humans, operating environment, and the voltage. Naturally, the best approach in avoiding the degrading circuit or danger of shock is to space traces distance away apart as much as possible, but most times, that distance doesn’t/ will not meet the requirements of creepage.

If looking towards the angle of a material with a good Comparative tracking index seems impossible, routing a slot between two traces can add to the creepage distance. The loss of electricity due to faulty insulation from one trace to the other on the laminate surface would need to move around the air gap. However, a vertical hindrance of insulating components could be stationed in the space, which would add to both the clearance distance and that of creepage.

Importance of Comparative Tracking Index

CTI 600 pcb material

HVTR testing and other high-standard voltage arcing tests are carried out on dry, solid insulation materials. Comparative tracking index testing is carried out with the application of liquid to the board surface. It is aimed at evaluating the opposition of the board’s insulation to track. In the presence of contamination, which is most likely for industrial boards, especially when entrenched in manufacturing equipment, as discovered in advanced industrial processing environments.

The Comparative tracking index is significant as it gives a quantitative metric by which materials that differ can be compared and a selection possible based on its chances to cope with its intended environment. Most especially, the Comparative tracking index can be adopted to ascertain clearance distance and creepage for your board’s design.

Comparative Tracking Index Testing Options

  1. UL testing facility: The best option is by testing by anUl facility if testing is needed. The Comparative tracking index test can be carried out with the related surface tracking estimation.
  2. Facility for other testing facilities: There are several companies that can carry out testing of materials for you. The benefit here is that you are not mandated to acquire or have the equipment that is necessary or the environment that meets the standards’ requirements.
  3. In-Door: if your anticipation is on the need to carry out this type of testing regularly, the expenses might worth acquiring equipment and expertise to get it done whenever it is required.

Additionally, you may make use of the result of past studies that are available, and that is compatible with your design. If accurately utilized, Comparative tracking index testing can assist you in picking the best materials, PCB layout, and coating that are protective for your industrial board.

Understanding CTI in line with PCB routing

In case when two PCB traces similarly and often happening at the same time, the dielectric materials should not at any time break down, and the dual traces should have the ability to carry current without any glitch. There are fewer chances of dielectric breaking down and direct shots. The dielectrics make sure that there is a presence of resistance at the dual traces.

One of the basic reasons why the dual traces might have a loss of electricity is as a result of the formation of contamination between traces, the voltage applied, temperature, and ecological conditions.  Comparative tracking index is the proportion of the susceptibility of the printed circuit board’s insulating materials to the electrical breakdown. Mathematically, the Comparative tracking index represents the voltage, which results in failure by breakdown after 50 drops of 0.1% ammonium chloride solution have failed on the material.

Creepage Distance and Comparative Tracking Index Value

Creepage distance is the shortest available path between the measured dual Printed circuit boards along the insulation surface. Depending on the Comparative tracking index value of the Printed circuit board, the creepage wild will experience a difference in value.

 If the Comparative tracking index records a higher value, then the minimal creepage value is needed. Lastly, a high Comparative tracking index value indicates the close tie between the Printed circuit boards.

Conclusion

In the fabrication of printed circuit boards, CTI is the measurement of the capability of the laminate external layer to be able to hold the outside layer, upon the release of an electrolyte between them.