PCF8564A datasheet(38/45 Pages) NXP

38 / 45 page

PCF8564A

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Product data sheet

Rev. 02 — 30 September 2010

38 of 45

NXP Semiconductors

PCF8564A

Real time clock and calendar

All NXP WLCSP packages are lead-free.

19.2 Board mounting

Board mounting of a WLCSP requires several steps:

1. Solder paste printing on the PCB

2. Component placement with a pick and place machine

3. The reflow soldering itself

19.3 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 35) than a PbSn process, thus

reducing the process window

• Solder paste printing issues, such as 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) while being 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 36.

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 35.

Table 36.

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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