stm7007 STMicroelectronics, stm7007 Datasheet - Page 13

• Manufacturer Part Number: stm7007
• Description: Single-chip Hardware Accelerated Encryption Engine For Computer And Peripherals Applications
• Manufacturer: STMicroelectronics

1.2.5
Rework guidelines
Because solder joints are not fully exposed with QFN packages, any touch-up is limited. For
defects underneath the package, the whole package must be removed. Because reflow of
adjacent parts is not desirable during rework, the proximity may complicate the rework
process. Because of the product-dependent complexities, the following provides only a
guideline and a starting point for the development of a successful rework process for this
package.
The rework process comprises the following steps:
1.
2.
3.
4.
Component removal
The first step in removal of the component is the reflow of solder joints attaching the
component to the PCB board. Ideally the reflow profile for part removal and attachment
should be the same, but this is not always possible.
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Site redress
After removing the component, clean the site properly.
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Solder paste printing
To achieve a uniform and precise deposition, use a miniature stencil specific to the
component.
Avoid tinning the lands, because the amount of solder applied to the lands cannot be
controlled.
Component placement and attachment
Although this type of package does display self-centering abilities, use care in its
placement.
Ideally, the reflow profile for part removal and attachment should be the same, but this
is not always possible.
Heat the board from the top side of the component.
Heat the board from the top side of the component.
Use a special nozzle to direct the heating in the component area.
Minimize the heating of adjacent components.
Start with an air velocity of 15 to 20 liters per minute.
Avoid excess heating and pad liftoff.
Use de-soldering braid to remove excess solder.
Once the residual solder is removed, clean the lands with solvent. The solvent is
usually specific to the type of paste used in the original assembly.
Doc ID 022239 Rev 1
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