Rework (electronics)

Rework is a term which refers to the rework or repair of electronic assemblies (English printed circuit board assembly, PCBA ) in the Surface Mount Technology ( surface mount technology ). The various work processes require most technically complex machines and concrete expertise of trained staff.

Reasons for rework

Production modules in the various test methods are used. These include, for example, the visual inspection by production staff, the ( automated optical inspection ) ( AOI), automated x-ray inspection, in-circuit test exam, the function test and the high voltage test.

If a missing or bad solder joint, a missing, misplaced, bent or defective component or a missing or defective circuit function is determined by a test procedure is done a rework of the assembly, where this is economically sensible. The rework station can include a soldering rework or replacement of components in this case.

In addition, the rework is also in the field of after-sales service (eg, warranty repair ) are used. Here is the repair of the module or device in the foreground.

In the course of a research or development project can be removed by a rework components replaced or additionally equipped.

Steps of the repair process

A repair process for SMD components is generally of the following steps:

When repairing, make sure that surrounding components are not melted and out of place. In practice, the IR soldering this is achieved by bonding of protective films that need to be checked at each step and, where necessary, re- placed. Hot gas repair stations provide this security by the design of the solder nozzle and the settings of the soldering profile. Adds a further optimized for the board soldering profile for safety. Here are systems that provide an intelligent heating for top and bottom heat, first choice. Any unnecessary thermal load of the module leads to premature aging and should be avoided whenever possible. Both the short term and the temperatures are to be kept only as low as it set the specifications of the component manufacturer, so as not to damage the component.

Value chain

When desoldering of an individual SMDs of the PCBA all solder connections between these two parts are melted and the components separated.

The array ( grid ) is cleaned on the circuit board from the solder sucker. By again heating up to the melting region, it is relatively easy to remove remaining residues of the dissolved solder joints. To avoid damaging the PCB, solder the rest should be paid to a non-contact distance. Furthermore, make sure that this process is kept as short as possible to avoid unnecessarily burdening the thermal circuit board.

For the exact positioning of the new SMD on the prepared pad array of expert needs a rework station, which is due to the optical resolution to be able to bring the ball of SMD as closely as possible to the contact surfaces of the circuit board cover. The smaller the pitch of the component, the higher the requirements to the rework station. Due to the change by the introduction of lead-free solders properties of the solder, the placement accuracy of the system should be higher at 10 microns or. An automatic device is not a prerequisite for precise placement, only the stability of the system and determine the optical resolution on the accuracy.

Finally, to solder the SMD just placed on the PCB. In order to produce reliable and high quality solder joints all solder joints between the new module and the PCBA heated with the appropriate soldering profile above the melting point and cooled properly.

Additional aspects

The value chain for the rework described above can be supplemented by special processes.

High quality standards or specific types of SMDs make the application of solder paste inevitable before placement may. For example, components in Quad Flat No leads package ( QFN / MLF ) or Quad Flat Package ( QFP ) are supplied without solder deposit. In order for a solution for the job fresh solder paste must be found. For this purpose, there are two possibilities:

For easy application of solder paste in the repair of Lotpastdruck recommend using stencil and squeegee. This method can easily, quickly and highly accurately performed. It is crucial that the same amount of solder as in the production, to the contact surfaces is applied. The second, but technologically more sophisticated variant is the dispensing of solder paste.

Sometimes the desoldered BGA or CSP can be reused. In this case, the component must be freed of residual solder. As with the printed circuit board are to be preferred herein contactless method, in order to protect the device from damage. Currently, it is already possible to the contact surfaces of a BGA 35x35 to clean without contact in a single step. Using a reballing Modules, which also works with templates that new ball will be applied to the component. The template is positioned exactly on the BGA and then populated with solder balls. In reflow process should be to improve the result to an inert atmosphere - be respected - as in the reflow oven.

Application in industry

Instruction to high quality and rework the correct function of the electronic assemblies restored. The life of the printed circuit board is hardly affected by the proper implementation of the rework value chain. Therefore, the rework is widely used in all sectors of the electronics industry. Its users include manufacturers of telecommunications equipment, entertainment and home appliances, industrial equipment, automotive, medical, aerospace and other high-power electronics, as well as their service providers.