Rework of Underfilled Components
When looking at surface mount technology, the field of rework appears more and more important due to economic considerations. Valuable raw materials and components, complex productions engineering and long value chains make advanced rework profitable. The difference between non-underfilled component removal and underfilled component removal mainly results from one specific preparation stage: mechanical clamping at the component and mechanical cleansing in order to remove residual underfill. By choosing an appropriate selection of tools and devices, a damage of the PCB with its pads, wires, circuit paths or the solder resist can be avoided. The local arrangement of heating systems and tools will protect the components placed at the bottom side and those neighboring the defective component. The rework process can be supported by using novel reworkable underfill materials which can be obtained in the market.
The whole rework process consists of the following steps:
- Preprocessing of the component
- Desoldering
- Residual underfill removal
- Solder removal
- Soldering of new component
- Underfilling and curing
Additional challenges are brought to the table by ever smaller components and increasingly smaller packing sizes. They demand a rework process capable of both, big and small-sized components with high or low stack heights. It also has to be ensured that underfill components neighbouring the defective component will not be damaged, deplaced or lifted together with the defective component.
When manually reworking underfilled components with soldering gun and tweezer, the process can hardly be controlled when it comes to fusibility. As soon as the solder is molten, conventional observation is no longer possible because of the typical characteristics of SMD components. Furthermore, the heat distribution is significantly determined by the underfill materials used in the process.
If the operator tries lifting the component while the solder is not yet molten enough, there is an extremely high risk that several pads will be destroyed. In this case the board will be damaged irreparably. On the other hand, the lifespan of a board and its interconnections could be drastically reduced when heated too long or at higher temperatures than recommended (thermal stress). Due to that fact, a hand rework of underfilled component will turn out very hard to control and poorly repeatable. Furthermore, a manual use of tools will be more and more impossible with densely packed next generation boards (pitch between components down to 300 µm!).
The intelligent COMISS reflow system allows a precise control of all environment variables having an impact on the rework process. The application-specific soldering process has to be created only once. Afterwards, this defined process can be reproduced for all rework cases of this application. This ensures that all rework processes will proceed under identical conditions – 100% independent of extraneous influences. This is as easy as manual rework can get! |
