July 6, 2020

CONFIDENTIAL INFORMATION v3.6

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ESS TECHNOLOGY, INC. 237 South Hillview Drive, Milpitas, CA 95035, USA. Tel (408) 643-

8800 • Fax (408) 643-8801

Reflow Process Considerations

For lead-free soldering, the characterization and optimization of the reflow process is the most important factor you need to

consider.

The lead-free alloy solder has a melting point of 217°C. This alloy requires a minimum reflow temperature of 235°C to

ensure good wetting. The maximum reflow temperature is in the 245°C to 260°C range, depending on the package size

(Table RPC-2). This narrows the process window for lead-free soldering to 10°C to 20°C.

The increase in peak reflow temperature in combination with the narrow process window makes the development of an

optimal reflow profile a critical factor for ensuring a successful lead-free assembly process. The major factors contributing to

the development of an optimal thermal profile are the size and weight of the assembly, the density of the components, the

mix of large and small components, and the paste chemistry being used.

Reflow profiling needs to be performed by attaching calibrated thermocouples well adhered to the device as well as other

critical locations on the board to ensure that all components are heated to temperatures above the minimum reflow

temperatures and that smaller components do not exceed the maximum temperature limits (Table RPC-2).

To ensure that all packages can be successfully and reliably assembled, the reflow profiles studied and recommended by

ESS are based on the JEDEC/IPC standard J-STD-020 revision D.1.

Figure RPC-1. IR/Convection Reflow Profile (IPC/JEDEC J-STD-020D.1)

Note: Reflow is allowed 3 times. Caution must be taken to ensure time between re-flow runs does not exceed the allowed time by the

moisture sensitivity label. If the time elapsed between the re-flows exceeds the moisture sensitivity time bake the board according to the

moisture sensitivity label instructions.

Manual Soldering:

Allowed up to 2 times with maximum temperature of 350 degrees no longer than 3 seconds.