DocID024655 Rev 3

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TN1037

Rework

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5.3

Reassembly and reflow

After preparing the site, the new package can be placed onto the PCB and the leads

inserted into the holes. Regarding placement accuracy and placement force, the process

should be comparable to the (automatic) pick & place process.

During the soldering process, it should be assured that the package peak temperature is not

higher and temperature ramps are not steeper than for the standard assembly process.

Soldering wire can be used to re-solder the leads. Use only no-clean solder paste, solder

wire, and flux for repair.

5.4

Coating of assembled PCBs

In some applications, coatings are used to prevent damage due to external influences such

as:

• Mechanical abrasion

• Vibration

• Shock

• Humidity

• Hand perspiration

• Chemicals and corrosive gases

These influences may cause:

• Electrical leakage due to humidity.

• Corrosion that leads to degradation of conductor paths, solder joints, and any other

metalized areas; and/or formation of electrical leakage paths. These can eventually result

in electrical shorts (electrical leakage) or open contacts.

• Mechanical damage to conductor paths, solder joints, and components. This damage can

lead to electrical failures.

Coatings act as electrically isolating and impervious covers that adhere well to the different

PCB materials.

A wide variety of different coatings are available on the market. They differ in:

• Price

• Simple processability (spray, dip, casting, curing, etc.)

• Reparability

• Controllability

• Homogeneity

In any case, please be aware of the chemical, electrical, mechanical and thermo-

mechanical interaction between the coating, the PCB and its components. Coatings can

affect component reliability.