The soldering temperature distribution of lead-free solder AOS products

Purpose
 

       This document specifies the recommended soldering temperature profiles applicable to all Alpha and Omega Semiconductor (AOS) products. During installation, using temperatures and durations that do not exceed these conditions can prevent component damage and help ensure the quality and reliability of AOS components.

Scope
 

      This procedure applies to all AOS products/components that require soldering on printed circuit boards (PCBs).

Reference document
 

       JESD22-A113 Preconditioning of Non-hermetic Surface Mount Devices Prior to Reliability Testing IPC/JEDEC J-STD-020D, Moisture/Reflow Sensitivity Classification for Non-hermetic Solid State Surface Mount Devices.

Overview
 

      The soldering curve is used for PCB assembly. Since different customers use different systems, components, and solder materials, the optimal soldering conditions to ensure solder integrity and reliability can only be determined by the user (customer).

The recommended soldering profile reflects the commonly used range during the PCB assembly process, with thermal stress lower than our reliability qualification preconditioning. This will ensure the long-term reliability of AOS parts.
      During reliability qualification, AOS parts will be subjected to very stringent conditions as per the IPC/JEDEC J-STD-20D document (see the curve in Appendix A). This includes one week of moisture soaking at 85°C and 85% relative humidity, followed by three reflow simulations with peak temperatures ranging from 255°C to 260°C, each lasting ≥30 seconds. Using temperatures and durations that do not exceed these recommended conditions will not damage the AOS parts.

Recommended soldering temperature profile

Reflow soldering curve

Figure 1. Recommended general soldering temperature profile for printed circuit board assembly. Ranges 1 to 5 correspond to

Table 1. Recommended General Welding Curves

Note:

         The maximum thermal deviation allowed during the reflow soldering assembly process is as follows:

1. Temperature: 255°C to 260°C

2. Peak insulation duration: 30 seconds

3. Return count: 3 times

    

Wave soldering curve
 

Figure 2 Recommended JEDEC standard-defined wave soldering curve 1-5 corresponds to Table 2

Table 2 Recommended Wave Soldering Profile

Lead-free components assembled on the back of the printed circuit board

Overall, wave soldering is suitable for the assembly of through-hole components. It is not recommended to assemble lead-free components on the backside of the printed circuit board. Additionally, all wave soldering operations must adhere to the standard temperature profile set by the Joint Electron Device Engineering Council (JEDEC).

If you need to mount components on the back of the printed circuit board using surface mount reflow soldering first, you must use special fixtures to prevent the components from falling into the wave soldering bath.

If adhesive is used to mount the device on the back of the printed circuit board, it is the customer's responsibility to ensure that the device does not fall off during the wave soldering process.

Surface-mount device packages suitable for wave soldering

According to the JESD22-A111 standard, surface-mount devices (SMD) with gull-wing leads and a moisture sensitivity level of 1 (MSL1) are suitable for wave soldering (IWS).

• Applicable package examples (but not limited to): SOT23, TSOP6, SOP-8, DPAK.

Surface-mount device packages not suitable for wave soldering

Surface-mount devices (SMD) with flat leads and a moisture sensitivity level of 1 (MSL1) are not suitable for wave soldering (IWS) due to the risk of leads being suspended caused by red glue.

Examples of such packages include (but are not limited to): DFN8x8, DFN5x6, DFN3x3, UltraSO8 (MSL1), TOLL (MSL1).

AOS does not recommend using any surface-mount device packages with a moisture sensitivity level of 3 (MSL3) during the wave soldering circuit board assembly process.

Manual welding

Not recommended for large-scale production. However, in engineering projects or rework situations, manual soldering is allowed but should be handled with caution.                                                                                                                       

Table 3 Manual Welding Parameters