Nxp Semiconductors SA58670A 用户手册

SA58670A_2

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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 19

) 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 7

 and

8

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 19

.

°

≥

< 2.5

235

220

≥

 2.5

220

220

°

< 1.6

260

260

260

1.6 to 2.5

260

250

245

> 2.5

250

245

245