NEWS // FEATURES // NEW PRODUCTS
Spray-In-Air Equipment There is a great variety of equipment using Spray-In-Air to provide the mechanical energy in our cleaning process. Depending on the manufacturer and the equipment
model, heating and rinsing may or may not be available as standard features or even as options.
Ultrasonic Equipment We can also fi nd a wide range of equipment using ultrasonics as mechanical energy for the cleaning process. Once again, manufacturer and equipment model will
determine whether heating and rinsing may or may not be available as standard features or options. While Spray-In-Air stencil cleaning equipment tends
to be automatic, ultrasonic equipment can be automatic and semi-automatic. In an automatic system, the user introduces the stencil in the cleaning chamber and the equipment will automatically wash, rinse (if available), and dry the stencil. In a typical semi-automatic system, the user has to manually move the stencil from the wash to the rinse and to the drying cycle. The rinse and the drying cycle could be completely manual steps. If heating is available, it can be very useful to speed up the cleaning of diffi cult soils such as some Pb-free pastes and some SMT adhesives. In any case, the temperature needs to be <50°C (122°F) and preferably, ≤45°C (113°F). If the temperature goes above these recommended settings, we could face serious compatibility issues with the stencils and if cleaning SMT adhesives, they could be cured rather than cleaned, thus making them almost impossible to clean. We recommend that equipment and chemistry be
chosen together when possible. If this is not possible, the key is to fi nd the balance in the Process Cleaning Rate (Rp = Rs + Rd).
V. Process Validation Stencil cleaning processes also require a thorough evaluation of the key elements and cleaning process parameters to verify that the process performs as expected. We, the chemistry suppliers, can provide a complete solution to our customers by using the knowledge and expertise about cleaning processes, no matter what the process is.
26 EIU
Manual Stencil Cleaning Manual cleaning is the least desired/recommended option for stencil cleaning. This process provides poor repeatability as it is operator dependent.
The operator is also directly exposed to chemicals, which in some cases could be hazardous to the health of the operator (caustic products, IPA, etc.) as sometimes proper safety measures are not taken. The picture on the right shows how stencil apertures could look if a manual cleaning process is not closely watched.
Summary In conclusion, as stated in the previous chapter of this series, the main elements to consider when creating or evaluating your stencil cleaning process are virtually the same as in PCB cleaning, the Soils (not all soils are equal), the Substrates (design, compatibility, etc.), the Chemistry (static energy) and the Equipment (dynamic energy). Cleaning chemical suppliers can be instrumental in selecting the correct cleaning process by providing the expertise and the laboratories needed to fi nd a complete cleaning solution that will meet your needs. Part 4 of this series will discuss Maintenance Cleaning and the fundamental considerations to have an effective and cost effi cient process.
Fernando Rueda is the Sales Manager for Kyzen BVBA. E-mail:
fernando_rueda@kyzen.com
References: Stach, S.; Bixenman, M. (2004, Sep.) Optimizing Cleaning Energy in Batch and Inline Spray Systems. Stach, S.; Bixenman, M. (2006) Optimizing Cleaning Energy In Electronic Assembly Spray In Air Systems: Phase II. Bixenman, M., Rueda, F., and Tuerlings, S. (November 2008). Innovative printed circuit board cleaning fl uid designed to remove process soils from populated assemblies, stencils, and rework in batch and inline cleaning equipment. Global SMT Romania Technical Conference. Romania. Bixenman, M. (2010, Sep.) Electronic Assembly Cleaning Process Considerations. Breed, S.; Pernice, R.; Stencil Printing SMT Adhesives: A Technology Review.
www.electronicscomponentsworld.com /
www.electronicsproductionworld.com January 14th 2012
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