NXP Semiconductors

PCA9537

4-bit I2C-bus and SMBus low power I/O port with interrupt and reset

• Process issues, such as application of adhesive and flux, clinching of leads, board

transport, the solder wave parameters, and the time during which components are

exposed to the wave

• Solder bath specifications, including temperature and impurities

14.4 Reflow soldering

Key characteristics in reflow soldering are:

• Lead-free versus SnPb soldering; note that a lead-free reflow process usually leads

to higher minimum peak temperatures (see Figure 20) than a SnPb process, thus

reducing the process window

• Solder paste printing issues including smearing, release, and adjusting the process

window for a mix of large and small components on one board

• Reflow temperature profile; this profile includes preheat, reflow (in which the board

is heated to the peak temperature) and cooling down. It is imperative that the peak

temperature is high enough for the solder to make reliable solder joints (a solder

paste characteristic). In addition, the peak temperature must be low enough that the

packages and/or boards are not damaged. The peak temperature of the package

depends on package thickness and volume and is classified in accordance with

Table 13 and Table 14

Package reflow temperature (°C)

Volume (mm³)

Package thickness (mm)

< 350

≥ 350

< 2.5

235

220

≥ 2.5

220

220

Table 13. SnPb eutectic process (from J-STD-020D)

Package reflow temperature (°C)

Volume (mm³)

Package thickness (mm)

< 350

350 to 2000

> 2000

< 1.6

260

260

260

1.6 to 2.5

260

250

245

> 2.5

250

245

245

Table 14. Lead-free process (from J-STD-020D)

Moisture sensitivity precautions, as indicated on the packing, must be respected at all

times.

Studies have shown that small packages reach higher temperatures during reflow

soldering, see Figure 20.

PCA9537

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© NXP B.V. 2021. All rights reserved.

Product data sheet

Rev. 7 — 8 September 2021

COMPANY PUBLIC

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