The height selection of conductive silicone strips and the problem of incomplete display

The Height Selection Of Conductive Silicone Strips And The Problem Of Incomplete Display

Table of Contents

As an efficient and low-cost connector, conductive silicone strip is commonly used between the display and the circuit board of electronic products. Choosing the right type of conductive silicone strip, especially the height, is important to improve the display.

Introduction to the conductive silicone strip of the connector and its design principle

Conductive silicone strip

Commonly used conductive silicone strips are divided into YL type, YP type, YS type, YI type, YE type, of which YS type conductive silicone strip is a commonly used humidifier type. Different types of conductive silicone strips have different insulation, conductive and outer hardness. The spacing of silicone strips is also divided into 0.05P, 0.10P and 0.18P. Among them, 0.18P conductive silicone strip is more commonly used and cheaper, and 0.18P YS type conductive silicone strip is used on the thermostat.

Design principle of conductive silicone strip connector

Length (L)/mm: The length of the glass where the gold finger is located is reduced by 0.5mm Height (H)/mm: The height between the LCD and the PCB × (1.10-01.15), that is, the compression ratio is 10%-15%.

Width (W)/mm: LCD edge width × (0.9-0.95) P value (pitch): The ratio of the width of each gold finger on the PCB to the glue strip is ≥3-5, that is, each gold finger has 3-5 conductive strips Layer contact, good electrical conductivity.

Application of conductive silicon connectors in electronic products

Due to the different types of displays (LCDs), the surface of the gold finger is also different, and the number and type of conductive connectors required are correspondingly different. In addition to displays and circuit boards, other structural components are required to support their applications. The length, width and height of the conductive silicone strip used depend on the specific circuit board and display.

A thermostat is a household product terminal that can precisely control the indoor temperature by controlling the switch of the central air conditioning system. As an electronic product with a user interface, it is also a conductive silicone strip used between the display and the circuit board. There is a gold finger on one side of the LCD screen, so conductive silicone strips are often used as a connector between the LCD and the PCB.

The thermostat display shows poor analysis results

Design dimensions of each component

In this structural module using conductive silicone strips, the housing of the thermostat is used as the outer frame bracket of the LCD, the light guide plate is used as the internal support of the LCD, and the conductive silicone strip is embedded in the cavity formed by the housing, LCD and light guide plate. Finally, cover the PCB board and secure it with screws. Figure 1.1 is the front view of the thermostat. As you can see, multiple sets of character information are displayed on the LCD. Figure 1.2 shows the structure and associated dimensions around the conductive silicone strip. As can be seen from the figure, although there are many structures near the conductive silicone strip, A and D play a key role in the size of the cavity in which the conductive strip is placed. Height space. (Although E and F are also in the mix, they are not directly related to the height of the conductive silicone strip.) According to the theory of cumulative tolerances, the spacing between the gold finger of an LCD and the PCB is 0.1043621″±0.0069″. Determine the placement space for the conductive silicone strip. According to the design principle of conductive rubber connectors, the compression ratio is best controlled between 10% and 15%. The limit value of the rubber strip that can be placed in the 0.1043621″ ±0.0069″ space can be calculated. Finally, delete the values at both ends (0.12795142″ and 0.1172346″ and take only the average of the median values (0.12238831″ and 0.112081415″) of 0.1172346″. The theoretical height (2.98mm) of this conductive silicone strip has a compression ratio of 12.4% relative to the theoretical gap. Based on the calculated height of the conductive rubber strip (2.98mm), a small batch of conductive rubber strips was customized and adjusted on the thermostat prototype. The connection effect is good and the display is normal.

Design dimensions of each componentDesign dimensions of each componentDesign dimensions of each component

The problem of poor display of the thermostat

The LCD screen used by the thermostat is a segment display and each character is displayed in segments. The thermostat equipped with this LCD was successfully produced, but in the subsequent series of functional verifications, it was revealed that some products had incomplete display characters. There are many reasons for this kind of failure, such as the screw is not firmly fixed, the display itself has display problems, PCB board problems, assembly problems, and connection conduction problems. We have ruled out and confirmed this one by one, and believed that the deviation of component tolerances resulted in insufficient height of the originally designed conductive silicone strips, resulting in poor connection between LCD and PCB. We measured the depth of space where conductive silicone strips can be placed at 3 positions A, B, and C of 5 groups of samples (LCD structural components). It was found that a 0.125″ high silicone strip should be placed. In order to better verify this choice, 0.123″, 0.125″, 0.126″ height silicone strip samples were arranged for the actual assembly test, and the three types of silicone strips were all normal function, but the conductive rubber strip with a height of 0.125″ (3.18mm) was used in the official production. The conductive silicone strip that was put into use later did not have poor contact and incomplete display fields in mass production.

In conclusion

As an efficient and low-cost connector, conductive silicone strips are widely used in electronic products. In the specific application, the appropriate type of conductive silicone strip should be selected, and the quality of the contact is closely related to the selection of its height. Since the conductive silicone strip needs to have a certain pre-compression deformation in the connected state, the choice of how much pre-compression is related to the quality of the conduction. The experience is that if the connection height is less than 4mm, the upper limit of the compression rate is about 15%; if the height is much larger than 4mm, the lower limit of the compression rate is 10%; if the height is in the middle, it is recommended to use the compression rate of about 13%.