What are the required characteristics of PTC thermostat heaters?
PTC heater manufacturers will generate force during the use of the PTC constant temperature heater, determine the power requirements of the PTC constant temperature heater, and ensure that the PTC constant temperature heater can be firmly connected. The mechanical characteristics of PTC thermostat heater are:
1. Insertion and extraction force
Purpose: To confirm that the force generated by the PTC constant temperature heater during use is sufficient to maintain the function of the PTC constant temperature heater and the feel suitable for consumers.
Test method: EIA-364-13 or MIL-STD-1344A, 2013.1.
Test points: a. The test object is the entire PTC constant temperature heater.
b. The test axis is the normal use direction of the PTC constant temperature heater.
c. Unless otherwise specified, the test speed is defined as 25.4mm/minute.
Specification requirements: a. The insertion force is generally set to a large value. (35N Max.).
b. The pull-out force is generally set to a small value. (7N Min. initial; 3N Min. Final), there are also customer requirements to set a large value.
The definition of the insertion force is to suit the consumer's hand feeling, and the definition of the pull-out force is to ensure that the PTC thermostatic heater remains connected under the condition of unexpected force, and does not cause the disconnection of the two connected products due to the unexpected force.
The insertion force is the force generated by the two matched PTC constant temperature heaters from completely separated to the working state; the pull-out force is the force generated by the two matched PTC constant temperature heaters from working state to the completely separated state. Plugging force is generated when consumers use the product, only the docking end (io/plug, jack/plug) will produce the plugging force, generally there is no docking end. The force curve produced during the test contains a lot of information. From the force curve, you can understand the stress state of the connection system during the insertion and removal process, and find out abnormal points for design improvement.
2. Locking force
Purpose: To confirm that the PTC constant temperature heater is subjected to unexpected conditions (force) during use, and the contact interface does not separate, so as to ensure the function under unexpected conditions (force).
Test method: N/A.
Test points: a. The test object is the entire PTC constant temperature heater.
b. The test axis is the normal use direction of the PTC constant temperature heater.
c. Unless otherwise specified, the test speed is defined as 25.4mm/minute.
Specification requirements: generally set a small value (30N Min.).
The locking force is the force produced by forcibly making two PTC thermostat heaters that match each other from working to complete separation under the condition that the locking mechanism is still working. This test is a destructive test, and the locking force in a self-locking or semi-self-locking system is equivalent to the pull-out force.
3. Retention
Purpose: to ensure the state (position) of the contact terminal (conductor) of the PTC constant temperature heater during the manufacturing or use process, and avoid external forces (such as the pulling of the wire during the manufacturing process; the thermal deformation force of the SMT process; the force when plugging and unplugging. The force generated by process shock or vibration, etc.) causes the contact terminal (conductor) to deviate from the working position, resulting in loss of connection function.
Test method: EIA-364-29 (EIA-364-05).
Test points: a. The test object is the entire PTC constant temperature heater.
b. The test axis is the normal use direction of the PTC thermostat heater (the opposite direction of the terminal assembly).
c. Unless otherwise specified, the speed is 25.4mm/minute.
e. It is a destructive test.
Specification requirements: generally set a small value (4.9N Min.).
The definition of the terminal retention force is to ensure that the terminal (conductor) is fixed in the plastic. The terminal assembled in the plastic is in the manufacturing process (such as welding/pulling during product handling/SMT process) and during use (such as male and female pairs). The plugging process, or the product is subject to vibration and impact) will receive external force, so the retention force of the terminal and the plastic must be sufficient, so that the terminal will not generate a PIN after being subjected to an unexpected force, which will cause the connection to be interrupted and the connection function to fail.
4. Positive force
Purpose: to maintain the positive contact stress of the PTC constant temperature heater during use, to ensure that the PTC constant temperature heater maintains sufficiently low contact resistance and friction during use; to ensure the connection function (no instantaneous interruption).
Test method: N/A.
Test points: a. The positive contact stress generated by the elastic contacts in the system under working conditions.
b. Unless otherwise specified, the speed is 25.4mm/minute.
Specification requirements: generally defined between 60-150gf (within the working period).
The definition of the positive force of the elastic terminal is to maintain a sufficiently low contact impedance and to prevent the product from being subjected to vibration or other unexpected forces during use to cause signal disconnection. The positive force refers to the force required to make the elastic terminal from the initial state to the working state.
It must be ensured that the positive force of the PTC thermostat heater is maintained before and after the life test or environmental test.
The relationship between the forward force of the terminal and the contact resistance is a reciprocal relationship. The positive force increases and the contact resistance decreases. When the positive force increases to 60gf, the magnitude of the decrease in contact resistance becomes very small. In addition, the greater the positive force, the greater the friction force generated during the contact process (f=F*u; f----friction force, F----positive force, u----coefficient of friction), The wear on the contact interface is more beneficial, so the general definition of the positive force does not exceed 150gf.
5. Life
Purpose: To confirm that the PTC constant temperature heater meets the functional requirements within the use limit.
Test method: EIA-364-09 or MIL-STD-1344A, 2016.1.
Test points: a. The test axis is the normal use direction of the PTC constant temperature heater.
b. Unless otherwise specified, the speed is generally 200-500cycles/H.
c. Generally, there is no current load during the test. (Unless additional requirements).
Specification requirements: a. The parameters to be determined during the test process and after the test: plug-in force (or positive force), contact resistance (terminal or iron shell), insulation resistance, withstand voltage, tightness, etc. meet the product specifications.
b. Visual inspection: wear, slack or fatigue, metal fragments, terminal displacement or bending damage, etc.
Life is also called durability (durability), which refers to the life span of the product. It is usually defined as the number of times of use to evaluate the wear condition of the terminal plating layer and the changes of the mechanical/electrical characteristics before and after the insertion and removal of the PTC thermostat heater after continuous use (plugging or positive pressure). The force curve generated during the life test can analyze the change and trend of the plug force before and after the life to assist in design correction. Before the life test, it is necessary to confirm that the sample has gone through a complete manufacturing process. For example, board end products need to pass SMT before entering the test program.
6. Appearance and size inspection
Purpose: To confirm the appearance and dimensional quality of the product (system).
Test method: EIA-364-18.
Test points: a. The appearance part defines the vision, light environment, sample placement, visual distance and time.
b. The size part defines the measuring instrument and measuring method, the requirements of the sample, etc. (such as the measurement after the molded plastic part is placed for 24 hours, etc.).
Specification requirements: a. Surface treatment requirements (such as plastic surface roughness; terminal plating), appearance requirements (such as no crushing; burrs).
b. The size meets the drawing requirements.
Other mechanical characteristics, PTC constant temperature heaters involve strength in the use process, such as the stability of the fit (such as the swing of the male and the female) and the stability of the combination (such as the anti-fall performance of the upper and lower shells of the finished product), etc. It needs to be added to the definition of the product specification when necessary.