The management of temperature and humidity sensitive components (such as humidity sensitive components HSM, some semiconductor devices, etc.) is crucial in the production process of PCBA (Printed Circuit Board Assembly). Improper environmental control may lead to component failure, poor soldering, and other issues, affecting product quality and reliability. The following will explain from the aspects of management points, operational norms, common problems, etc.:
Table of Contents
1、 Definition and classification of temperature and humidity sensitive components
1. Humidity Sensitive Components (HSM)
-Definition: Refers to components that are prone to absorbing moisture in humid environments and can cause packaging cracking, delamination, or internal damage due to water vapor expansion during welding, such as QFP, BGA, CSP and other packaged ICs, some LED devices, connectors, etc.
-MSL (Moisture Sensitivity Level): According to JEDEC J-STD-020 standard, it is divided into 1-6 levels, with higher levels being more sensitive to humidity and exposure time (for example, MSL Level 3 components should not be exposed to non dry environments for more than 48 hours).
2. Temperature sensitive components
-Definition: Refers to components such as electrolytic capacitors, crystal oscillators, and some sensors that may experience performance degradation or damage if the operating or storage temperature exceeds the specified range.
-Characteristics: High temperature may cause electrolyte evaporation in electrolytic capacitors, while low temperature may cause crystal frequency shift.
2、 Core management objectives
-Control environmental humidity: Avoid damage to components due to thermal stress during welding after moisture absorption.
-Control environmental temperature: prevent component performance degradation or physical damage caused by abnormal temperature.
-Standardize storage and operation processes: reduce component failures caused by human errors.
3、 Storage Management Standards
1. Storage environment requirements
-Humidity control:
-For MSL Level 1 components: can be stored in a normal environment (humidity ≤ 60% RH).
-For MSL 2-6 level components: they need to be stored in a drying cabinet with humidity ≤ 10% RH, or sealed in a moisture-proof bag with desiccant.
-Temperature control:
-Most components are recommended to be stored at a temperature of 15-30 ℃, avoiding direct sunlight or being close to heat sources such as heaters or equipment vents.
-Temperature sensitive components (such as electrolytic capacitors) must be stored strictly according to the specifications (such as -10 ℃~40 ℃).
2. Key points for storage operations
-Moisture proof bag management:
-Unopened moisture-proof bags need to check the humidity indicator card (HIC). When the indicator card shows that the humidity exceeds the threshold (such as MSL level 3 corresponding humidity ≥ 20% RH), it needs to be re dried.
-After opening, the components must be welded within the specified time (according to MSL level, such as 48 hours for MSL level 3), otherwise they need to be resealed or placed back in the drying cabinet.
-Drying cabinet usage:
-The drying cabinet needs to be powered on 24 hours a day, with real-time monitoring of humidity (≤ 10% RH) and temperature (15-30 ℃), and regular calibration of sensors.
-When placing components in the drying cabinet, it is necessary to record the placement time, quantity, and MSL level.
3. Labels and Identification
-Each component packaging must be labeled with MSL grade, opening time, expiration date (exposure time limit), and storage temperature/humidity requirements.
-Example tags:
| ┌──────────────────────────────────┐ │ Component Name: XXX IC │ MSL Level: Level 3 │ Opening time: July 1, 2025 09:00 │ │ Allowable exposure time: 48 hours │ │ Storage conditions: Temperature 15-30 ℃, humidity ≤ 10% RH │ └──────────────────────────────────┘ |
4、 Operational standards during the production process
1. Workshop environment control
-Temperature and humidity monitoring: It is recommended to maintain a temperature of 22 ± 3 ℃ and a humidity of 40% -60% RH in the production workshop (for MSL level 3 and above components, the humidity should be ≤ 50% RH).
-Equipment heat dissipation management: Reflow soldering, wave soldering and other equipment need to be well cooled to avoid local high temperatures affecting surrounding components.
2. Material retrieval and unpacking operations
-When retrieving materials from the drying cabinet, it is necessary to wear finger cots or gloves to prevent sweat from touching the components.
-Before unpacking the moisture-proof bag, the components need to be equilibrated in the workshop environment for at least 1 hour (to prevent condensation), and the HIC should be checked again.
3. Welding process control
-Reflow soldering temperature curve: Set according to the temperature resistance level of the component, for example, the peak temperature of MSL level 3 components usually does not exceed 260 ℃, and the insulation time needs to meet the requirements of the specification (to avoid overheating and water vapor expansion).
-Preheating treatment: For components exposed to a humid environment for a long time (beyond the exposure time), pre baking and dehumidification are required:
-Common baking conditions: 125 ℃± 5 ℃, baking for 24 hours (for MSL Level 3 components), to be carried out in accordance with JEDEC standards or manufacturer recommendations.
4. Handling of unused components
-The MSL 2-6 level components that were not used up on the day need to be resealed in moisture-proof bags and placed in a drying cabinet, while updating the opening time record.
-Components that have exceeded the exposure time need to be re baked and tested (such as visual inspection, functional testing), and confirmed to be qualified before use.
5、 Personnel training and record management
1. Personnel training
-Operators need to receive training on temperature and humidity sensitive component management, master MSL level recognition, use of drying cabinets, baking processes, and other knowledge.
-The training content includes: calculating the exposure time of moisture-proof bags after opening, reading humidity indicator cards, and handling procedures for abnormal situations (such as component moisture).
2. Recording and tracing
-Establish a ‘Temperature and Humidity Sensitive Component Management Ledger’ to record component models, MSL levels, storage times, storage locations, opening times, usage batches, and remaining quantities.
-Record the temperature, humidity, and workshop environment data of the drying cabinet daily, and keep them for at least 2 years for traceability.
6、 Common Problems and Solutions
| Problem scenario | Possible causes | Solution |
| Cracks or delamination occur after component welding | Component expands upon moisture absorption | Strictly control storage humidity and use within the exposure time after opening; If it exceeds the time limit, it needs to be baked and dehumidified. |
| Abnormal capacity of electrolytic capacitor | Excessive storage temperature leading to electrolyte deterioration | Ensure that the storage temperature is within the specification range and away from heat sources; Check the appearance and parameters of temperature sensitive components before use. |
| After opening the moisture-proof bag, the humidity indicator card changes color | Poor sealing or desiccant failure | Replace with a new desiccant, reseal and check the seal; Calibration or maintenance is required when the humidity in the drying cabinet is abnormal. |
| Crystal oscillator frequency offset | Welding temperature too high or storage temperature fluctuation large | Optimize reflow soldering temperature curve to avoid local overheating of crystal components; Maintain temperature stability during storage. |
7、 Extension: The combination of ESD (electrostatic discharge) and temperature and humidity management
-Humidity control and ESD protection complement each other: when the environmental humidity is below 30% RH, the risk of static electricity increases, so the workshop humidity needs to balance the requirements of “anti moisture absorption” and “anti-static” (usually controlled at 40% -60% RH).
-Wear an anti-static wristband during operation, and lay anti-static pads on the workbench to avoid damage to sensitive components caused by electrostatic discharge.
Summarize
The management of temperature and humidity sensitive components in PCBA production needs to run through the entire process of “storage retrieval welding inspection”. Through standardized environmental control, operating procedures, and record traceability, the risk of component failure can be effectively reduced and product reliability can be improved. It is recommended that enterprises develop detailed management manuals based on JEDEC standards, component manufacturer specifications, and their own process characteristics, and regularly optimize processes.
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