SC28L92 datasheet(69/73 Pages) NXP

69 / 73 page

SC28L92_7

Product data sheet

Rev. 07 — 19 December 2007

69 of 73

NXP Semiconductors

SC28L92

3.3 V/5.0 V Dual Universal Asynchronous Receiver/Transmitter

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 27) than a PbSn 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 69 and 70

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 27.

Table 69.

SnPb eutectic process (from J-STD-020C)

Package thickness (mm)

Package reﬂow temperature (

°C)

Volume (mm3)

< 350

≥ 350

< 2.5

235

220

≥ 2.5

220

Table 70.

Lead-free process (from J-STD-020C)

Package thickness (mm)

Package reﬂow temperature (

°C)

Volume (mm3)

< 350

350 to 2000

> 2000

< 1.6

260

1.6 to 2.5

260

250

245

> 2.5

250

245

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