What type of solder paste is needed for smart wearables?

Intelligent wearable devices in the production process on the choice of solder paste need to consider the welding process, component characteristics, reliability requirements and environmental standards, the following is a specific analysis:

1. Types of soldering processes

Reflow soldering (SMT process)

The motherboards, sensors, and other precision components of smart wearable devices usually use surface mount technology (SMT), which requires the use of special solder paste for reflow soldering. This type of solder paste needs to have the following characteristics:

Low residual active agent: Reduces the need for cleaning and avoids corrosion of sensitive components (e.g. MEMS sensors, flexible circuits).

Fast melting characteristics: Adapt to the temperature rise curve of high-speed reflow ovens to prevent components from shifting or standing monuments.

Fine Pitch Compatibility: Supports soldering of components with a pitch of 0.3mm and below (e.g. 0201, 01005 packages).

Wave soldering (THT process)

If the device contains through-hole components (e.g. connectors, buttons), special solder paste for wave soldering is required, and its characteristics include:

High viscosity: prevents solder paste from dripping or bridging during the soldering process.

Thermal shock resistance: to adapt to the wave soldering process of high temperature immersion tin (usually 260-280 ℃).

2. Component characteristics and material compatibility

Lead-free requirements

Smart wearable devices need to comply with RoHS and other environmental regulations, give priority to lead-free solder paste (such as SAC305, containing 96.5% tin, 3% silver, 0.5% copper).

Advantages: environmentally friendly, moderate melting point (about 217-220°C), compatible with most components.

Note: Need to match the lead-free soldering process to avoid cold soldering due to insufficient temperature.

Special Component Adaptation

Flexible Printed Circuit Board (FPC): Low residue, low stress solder paste is required to prevent the flexible substrate from cracking due to thermal expansion or residue.

High-frequency components (e.g., Bluetooth, Wi-Fi modules): low hygroscopicity solder paste is selected to avoid signal attenuation due to moisture absorption after soldering.

Micro components (such as 0201, 01005 package): need ultra-fine powder solder paste (such as Type 5 or Type 6 powder) to ensure solder uniformity.

3. Reliability requirements

Temperature Resistance

Smart wearable devices may experience extreme temperatures (e.g., low temperatures during outdoor exercise or high temperatures during charging), high reliability solder pastes need to be selected to ensure that the solder joints are free from cracking or peeling off in the range of -40℃ to +85℃.

Vibration Resistance

Devices need to withstand the vibration of daily movement, solder paste needs to have good wettability, the formation of uniform solder joints to reduce the risk of false soldering.

Long-term stability

Select solder paste with strong oxidation resistance and long storage period to avoid degradation of printing performance due to long storage time.

4. Environmental Protection and Compliance

Halogen Free Requirements

Some devices are required to meet halogen-free standards (e.g., IEC 61249-2-21), and halogen-free solder pastes need to be selected to avoid halogen residues that could be harmful to components or the human body.

Certification Standards

Ensure that the solder paste meets the relevant industry standards (e.g. IPC J-STD-004, J-STD-005) and passes the reliability tests (e.g. high-temperature and high-humidity storage, temperature cycling tests) of the equipment manufacturer.

Recommended solder paste types

SMT process (motherboards, sensors):

Lead-free reflow solder paste (e.g. SAC305) is recommended, with features such as low residue, fine pitch compatibility, and fast melting.

Wave soldering (through-hole components):

Recommended lead-free wave solder paste (high viscosity type), with thermal shock resistance, anti-bridging and other characteristics.

Flexible Printed Circuit (FPC):

We recommend low-stress lead-free solder paste with low residue, low thermal expansion, and compatibility with flexible substrates.

Miniature components (0201/01005 package):

Recommended ultra-fine powder lead-free solder paste (Type 5/6), with uniform printing, anti-monumentation, high reliability and other characteristics.

High frequency components (Bluetooth/Wi-Fi):

Recommended low moisture absorption lead-free solder paste, with low dielectric loss, stable signal transmission and other characteristics.

Overall:

Smart wearable devices need to choose solder paste according to the specific process (SMT/wave soldering), component type (lead-free, miniature, high-frequency) and reliability requirements. Priority is given to recommending lead-free, low-residue, high-reliability solder pastes, and ensuring compliance with environmental regulations and industry certification standards. In actual production, it is recommended to verify the compatibility of solder paste with equipment materials through sample testing to optimize solder quality.