PCA2000USLASHAB datasheet(24/28 Pages) NXP

24 / 28 page

PCA2000_2001_5

Product data sheet

Rev. 05 — 11 November 2008

24 of 28

NXP Semiconductors

PCA2000; PCA2001

32 kHz watch circuit with programmable adaptive motor pulse

13.4 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 18) 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 14 and 15

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 18.

Table 14.

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 15.

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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