CMA3000 Assembly Instructions

6

Rework Guidelines

There are several rework systems on the market. Some will heat solder joints directly from the

sides of component package, while others will direct heat on the top of component. Occasionally,

very rough rework methods are used such as hand placement and heating with a soldering iron.

However, these rough methods are not recommended for CMA3000 component. It is

recommended that the heat flow of hot-air convection directed at the edge and under the

component body directly to the solder joints and component pad areas would be used. Secondary

methods include a horizontal flow method, a conduction method, and a conduction heating from

the top of the package.

6.1

Preparations

Prior to the rework process, PWBs and components should be free from moisture. If necessary,

baking and drying processes should be performed.

The reflow profile for the component removal should be similar to the normal reflow process. A

carefully adjusted reflow profile is essential for the successful rework operation. A proper reflow

profile should be measured with thermo-couples. During the reflow profiling, at least the solder

joints, the top of the component, and the bottom of the PWB should be monitored. If there are

other components near the component to be reworked, the temperatures of those should also be

monitored. The bottom side heating of the PWB is recommended in order to reduce the PWB

warpage during the rework operation.

6.2

Component removal

Once the solder joints have been fully melted, the component can be carefully removed from the

PWB. The common rework methods for the component removal can be used, i.e. a vacuum nozzle

etc. It is absolutely necessary to ensure the complete melting of the solder joints before the

component lifting. If the solder joints are not fully melted before the lifting operation, pad damage

may occur on the PWB and the component.

6.3

PWB cleaning

After the component is removed, the pad areas of the PWB should be cleaned using common

rework methods. These include the applying of a rework flux, an excess solder and flux removal

using a vacuum solder removal tool or a solder wick and a soldering iron with a wide chisel tip, and

the cleaning of solder pads with alcohol and brush. The PWB cleaning process should be

performed gently as too high force or a scrubbing motion can cause pad lifting and trace damage.

6.4

Component reuse

It is not recommended to reuse the component.

6.5

Applying flux or solder paste

Prior to the placement of a replacement component onto the reworked PWB, solder paste or flux

should be applied onto the cleaned PWB pads. Recommended methods for applying solder paste

or flux are the usage of a micro-stencil or dispensing. If the micro-stencil is used, it should be

cleaned after each paste application to prevent clogging. For the solder paste and the stencil, the

same guidelines as for the normal reflow process should be used. The usage of solder paste over

mere flux is recommended due to an increased stand-off.

Subject to changes

TN68

15/18

Rev.09

PRELIMINARY

VTI Technologies Oy

www.vti.fi