ACDi has noticed an increase in customer inquiries into the types of equipment required to perform efficient rework for simpler projects in house. So, we thought we’d poll our manufacturing engineering staff for advice regarding the top five “must haves” for simple rework. For my first blog assignment at ACDi, I enlisted the assistance of Kenny and Andrew, two of ACDi’s manufacturing engineers. Not only did they give some great advice, but I have been able to greatly expand my knowledge and gain insight into what it takes to provide quality rework for PCBs, and I am excited to have accomplished one of my first major tasks! I hope you enjoy.
Before beginning rework, there are challenges to consider outside of the obvious process of heating the component enough for removal from the board. First, while rework appears to be a rather basic process, careful consideration must be taken regarding all of the variables involved in the process. With the increased use of lead-free solders and thicker printed circuit boards with smaller surface area, different methods become necessary in order to preserve the functionality, reliability, and longevity of the surrounding components on the PCB. As the complexity of the PCB increases, so do the procedures necessary for the rework.
The two main processes involved in rework are either reflowing, or removal/replacement. Reflowing would be used if insufficient solder has been applied, or there are places missing solder altogether. Removal/replacement would require the removal of the component that was originally placed followed by the placement of a new component.
Hot air tools provide a comparatively inexpensive option for rework and the fact that only air is being applied can assist in reducing the likelihood of damaging components through contact. Temperature and air flow can be controlled manually or through profiling, and a machine with profiling capabilities is highly recommended as it provides a reduction in the number of cracked joints that can occur from rework and thermally stressing the components. Hot air tools have exchangeable tips to assist in the directing of the air to prevent damage to surrounding components, and also have the capability of heating large areas.
A solder extractor with a desoldering head contains a vacuum providing the removal of the solder as well as the component. This tool provides two functions in one hand, allowing the operator more freedom and stability during the process, as well a providing a less costly alternative to the use of solder braids. Caution has to be taken though, to prevent buildup in the tips used for removal as the solder cools.
Ovens or infrared (IR) hot plates can be used to preheat boards, reducing the risks of damaging the boards as well as ensuring that the boards stay within the suggested temperature profiles. Lead-free solder requires higher temperatures to turn to a liquid state, therefore preheating prevents extensive rework time that may overexpose the board and components to longer than recommended high temperatures. Preheating also assists in assuring that any heat sinks within the board reach the desired temperatures before beginning rework, and much like preheating used in the SMT or wave machines, it provides an even distribution of heat to prevent shocking components.
The ERSA HR 100 Hybrid has allowed ACDi greater control and flexibility when doing rework on the decreasing sizes of components required for the intricate projects requested by our customers. A rework essential item, the ERSA Hybrid allows for varying methods of rework depending on the complexity of the project. The hot air features allow for fast heating and removal of leaded and lead-free solders, as the temperatures can be adjusted to reach the necessary heat ranges for each application. For rework involving fine pitch components, the infrared (IR) features ensure the safety and reliability of the surrounding components. The IR allows the temperatures to be more easily controlled and evenly distributed, while decreasing the risks of thermally shocking surrounding components or blowing off components using only the hot air method. This model is also cost effective in comparison to other larger rework stations.
Lastly, ACDi recommends use of an AOI or x-ray machine to qualify the work done and to determine the conformance level of the rework. The focus of rework should always be to create an end product that does not differ from the original specifications of the client.
Do you have any other rework tips or questions you would like to share? Feel free to comment and ask away in the comment form below.