PCF8574; PCF8574A
NXP Semiconductors
Remote 8-bit I/O expander for I2C-bus with interrupt
• 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
17.4 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 21) 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 11 and 12
Table 11. SnPb eutectic process (from J-STD-020D)
Package thickness (mm) Package reflow temperature (C)
Volume (mm3)
< 350
235
350
220
< 2.5
2.5
220
220
Table 12. Lead-free process (from J-STD-020D)
Package thickness (mm) Package reflow temperature (C)
Volume (mm3)
< 350
260
350 to 2000
> 2000
260
< 1.6
260
250
245
1.6 to 2.5
> 2.5
260
245
250
245
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 21.
PCF8574_PCF8574A
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© NXP B.V. 2013. All rights reserved.
Product data sheet
Rev. 5 — 27 May 2013
23 of 33
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