To conduct heat resistance testing on PCB boards, it is necessary to combine industry standards and specific application requirements. The following is a detailed guide that integrates multiple testing methods:
Table of Contents
1、 Core testing methods and standards
1. Thermal shock test (simulating extreme temperature changes)
-Purpose: To evaluate the stress resistance of PCB under rapid temperature changes, detect delamination, cracks, or electrical performance failures.
-Equipment: Two box or three box thermal shock testing machine, supporting rapid switching between high temperature (such as 125 ℃) and low temperature (such as -55 ℃) environments.
-Standard:
-IPC-TM-650 2.6.7 series: specifies the heat shock resistance requirements for conformal coating, solder mask, and overall PCB, such as temperature cycling times (usually 500-1000 times) and holding time (15 minutes/cycle).
-GB/T 39342-2020 (Aerospace Standard): It is required to cycle 100 times from -65 ℃ to 125 ℃, with an interconnect resistance change rate of ≤ 10%.
-Steps:
1. Place the sample in a high temperature zone (such as 125 ℃) for 15 minutes, quickly switch to a low temperature zone (such as -55 ℃) for 15 minutes, and repeat the cycle.
2. After testing, check the appearance (without delamination or bubbles) and measure the resistance change. Slice and analyze whether the copper holes are cracked.
2. Thermal stress testing (evaluating the heat resistance limit of the substrate)
-Purpose: To verify the structural stability of PCB at high temperatures and detect defects such as board bursting and delamination.
-Equipment: Constant temperature tin furnace (temperature accuracy ± 5 ℃), TMA (thermal mechanical analyzer).
-Standard:
-IPC-TM-650 2.6.8: The sample is required to be immersed in a 288 ℃ tin furnace for 10 seconds without delamination or solder mask detachment.
-Industry experience: FR-4 substrates typically require at least 5 cycles of 288 ℃ tin immersion, while HTg materials require at least 10 cycles.
-Steps:
1. Sample a 10 × 10cm substrate, polish the edges, and bake in a 105 ℃ oven for 2 hours to remove moisture.
2. Immerse in a 288 ℃ tin furnace for 10 seconds and observe whether there are bubbles or layers on the surface. If it does not fail, repeat the test until the board bursts, and record the number of cycles.
3. Glass transition temperature (Tg) test
-Purpose: To evaluate the heat resistance of materials based on their thermal characteristics. The higher the Tg value (such as ≥ 150 ℃), the better the dimensional stability at high temperatures.
-Equipment: Differential Scanning Calorimeter (DSC), heating rate of 20 ℃/min, scanning to a temperature higher than the expected Tg value.
-Standard: IPC-TM-650 2.4.24, requires repeated scanning twice and taking the average Tg value.
4. Explosion board test (evaluating the temperature resistance limit of the substrate)
-Purpose: To quantify the delamination time of PCB at high temperatures, and the longer the board explosion time, the better the heat resistance.
-Equipment: TMA tester, set probe pressure to 0.005N, heating rate from 10 ℃/min to 260 ℃, and maintain constant temperature for 60 minutes.
-Steps:
1. After sample pretreatment (baking at 105 ℃ for 2 hours), raise the temperature to 260 ℃ in TMA and maintain it, and record the time of stratification.
2、 Other auxiliary testing methods
1. High temperature storage test
-Purpose: To evaluate the material aging of PCB under long-term high temperature environment (such as discoloration of solder mask and oxidation of copper foil).
-Equipment: Constant temperature chamber, usually set at 125 ℃ or 150 ℃, lasting for 24-1000 hours.
2. Lead free soldering test
-Purpose: To verify the reliability of solder joints at high temperatures and simulate lead-free soldering conditions (260 ℃ tin bath, 3-5 seconds).
-Equipment: lead-free soldering furnace, flux, 10x magnifying glass for checking wetting effect.
3. Acid and alkali resistance test
-Purpose: To evaluate the chemical stability of solder mask at high temperatures and prevent the dissolution of green oil during welding.
-Step: Immerse the sample in a 10% sulfuric acid or sodium hydroxide solution for 30 minutes, dry it, and test the adhesion with tape.
3、 Preparation and precautions before testing
1. Sample processing:
-Cut the sample to standard size (such as 6.35 × 6.35mm) and polish the edges to avoid stress concentration.
-Moisture absorbing materials (such as FR-4) need to be baked in a 105 ℃ oven for 2 hours to remove moisture and prevent bursting during testing.
2. Equipment calibration:
-The temperature of the tin furnace needs to be calibrated with a contact thermometer to ensure an accuracy of ± 5 ℃.
-The thermocouple should be firmly fixed (such as high-temperature solder or tape) to avoid detachment during testing and affect data accuracy.
3. Environmental control:
-The testing environment should be kept dry to avoid humidity affecting insulation performance.
-After high temperature testing, the sample needs to be cooled to room temperature in a dryer to prevent damage from condensed water.
4. Data analysis:
-Record the temperature curve, resistance change rate, and appearance defects during the test, and slice and analyze the internal structure (such as copper cracking).
-Compare IPC or customer standards to determine if it is qualified (such as resistance change ≤ 5%, board burst time ≥ industry threshold).
4、 Industry differences and special requirements
-Consumer electronics: Usually adopts a cold and hot shock test of -40 ℃ to 125 ℃, 500 cycles, with a focus on the integrity of the solder mask.
-Automotive electronics: It needs to pass the AEC-Q200 standard, with more stringent testing (such as -55 ℃ to 150 ℃, 1000 cycles), and requires solder joints to resist vibration fatigue.
-Aerospace: Following GB/T 39342-2020, the temperature shock range is wider (-65 ℃ to 125 ℃), and the resistance change rate requirement is stricter (≤ 10%).
5、 Recommended testing equipment
-Cold and hot shock testing machine: Three box type (such as ESPEC SH-662) supports high-precision temperature control and fast switching.
-DSC and TMA: TA Instruments Q2000 (DSC) and Q400 (TMA) are used for material thermal property analysis.
-Automatic testing machine: such as the equipment in X technology patent, integrating heat-resistant zone and tin dipping zone to achieve automated testing.
By using the above methods, the heat resistance of PCB boards can be comprehensively evaluated to ensure their reliability in high-temperature environments. Actual testing needs to combine industry standards and product requirements, flexibly adjust parameters, and strictly follow operating procedures.
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