Philips Semiconductors

PIP202-12M

DC to DC converter powertrain

Product data

Rev. 01 — 15 July 2002

16 of 20

9397 750 10031

© Koninklijke Philips Electronics N.V. 2002. All rights reserved.

15.2 Rework guidelines

Since the solder joints are largely inaccessible, only the side fillets can be touched

up. If there are defects underneath the package, then the whole package has to be

removed.

The first step in component removal is to reflow the solder joints. It is recommended

that the board is heated from the underside using a convective heater whilst hot air or

gas is directed at the upper surface of the component. Nozzles should be used to

direct the hot air or gas to minimize heating of adjacent components. Excessive

airflow should be avoided since this may cause the package to skew. An airflow of 15

to 20 liters per minute is usually adequate.

Once the solder joints have reflowed, the component should be lifted off the board

using a vacuum pen.

The next step is to clean the solder pads using solder braid and a blade shaped

soldering tool. Finally, the pads should be cleaned with a solvent. The solvent is

usually specific to the type of solder paste used in the original assembly and the

paste manufacturers recommendations should be followed.

16. Mounting

16.1 PCB design guidelines

The terminals on the underside of the package are rectangular in shape with a

rounded edge on the inside. Electrical connection between the package and the

printed-circuit board is made by printing solder paste onto the PCB footprint followed

by component placement and reflow soldering. The PCB footprint shown in Figure 20

is designed to form reliable solder joints.

The use of solder resist between each solder land is recommended. PCB tracks

should not be routed through the corner areas shown in Figure 20. This is because

there is a small, exposed remnant of the leadframe in each corner of the package, left

over from the cropping process.

Good surface flatness of the PCB lands is desirable to ensure accuracy of placement

after soldering. Printed-circuit boards that are finished with a roller tin process tend to

leave small lumps of tin in the corners of each land. Levelling with a hot air knife

improves flatness. Alternatively, an electro-less silver or silver immersion process

produces completely flat PCB lands.