Nxp Semiconductors LPC2917 User Manual

LPC2917_19_1

© NXP B.V. 2007. All rights reserved.

There is no soldering method that is ideal for all surface mount IC packages. Wave 
soldering can still be used for certain surface mount ICs, but it is not suitable for fine pitch 
SMDs. In these situations reflow soldering is recommended.

Typical dwell time of the leads in the wave ranges from 3 seconds to 4 seconds at 250

°C 

or 265

°C, depending on solder material applied, SnPb or Pb-free respectively.

The total contact time of successive solder waves must not exceed 5 seconds.

The device may be mounted up to the seating plane, but the temperature of the plastic 
body must not exceed the specified maximum storage temperature (T

stg(max)

). If the 

printed-circuit board has been pre-heated, forced cooling may be necessary immediately 
after soldering to keep the temperature within the permissible limit.

Apply the soldering iron (24 V or less) to the lead(s) of the package, either below the 
seating plane or not more than 2 mm above it. If the temperature of the soldering iron bit is 
less than 300

°C it may remain in contact for up to 10 seconds. If the bit temperature is 

between 300

°C and 400 °C, contact may be up to 5 seconds.

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 16

) 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 32

 and

33