The future of batch PCB cleaning
21 January 2013
There are many reasons why companies clean boards, for example to ensure no flux-residues are left in test areas, conformal coating or for high reliability circuits.
Despite all the research and R&D that has taken place already, cleaning still requires more evolution because there are still problem areas and new technologies have also inspired change.
Modern component technology such as BGA, Flip-Chip or low-profile components make flux residue entrapment more probable. Solder balls might also be present although they are difficult to see and find. Therefore, a comprehensive cleaning system that can get rid of unwanted residues is becoming a necessity with many manufacturers. If cleaning can keep up with production at negligible cost, process integrity can be maintained and manufacturers are more able to guarantee quality.
Previously, the available choices boiled down to either high-speed in-line or lower volume batchIn-line high-speed systems tended to be huge aqueous systems that were very expensive to buy and run and required a lot of space and money to clean high speed circuit volumes. Volumes are still high but the world has become more conscious of economy, both in terms of cost and floor space. Therefore we need batch systems that can cope with high speeds, are more floor efficient and have a low cost-of-ownership.
CEM’s need to provide this service but they also need to watch budgets carefully as margins are already thin. This does not mean that huge in-line systems have become dinosaurs, but they are no longer the immediate cleaning solution of choice. The need for high speed cleaning still exists though. If cleaning can be carried out without major impact on the production process, why not do it?
Kolb Cleaning Systems has been developing chemicals and equipment for electronics cleaning applications for many years. The economics versus speed debate stimulated a lot of R&D activity and the result is its new PSB500/600 range that can clean eurocard-sized boards in around 10 seconds. This is due to the increase in the vertical height of the machines, which allows a capacity of 8.6 square metres of circuit boards in one batch. They are still compact machines and occupy the same floor area as previous machines (about 2 square metres with an allowance for maintenance access) and so they fulfil the need for low floor space.
Clearly, the total cost of ownership depends on the choice of chemistry and other factors such as the amount of de-ionised water consumed. In any case the consumption of energy needs to be kept to an absolute minimum. Energy is consumed to power electric motors or pumps, operate driers and purify water if required. Other factors such as switches, controls or sensors also consume energy but at lower levels. The crucial energy factors are motors, pumps or driers. A Kolb system is designed to use around 2.3Kw of energy per process cycle.
Batch machines, as their name implies, are not intended to fit into a line but work alongside it. But they must be capable of keeping up with the required production rate. Batch systems offer huge flexibility; products of any size or shape can be cleaned whenever required. There are no conveyors to adjust and so a batch of eurocards can be followed by a batch of back-planes for example.
More and more products are being conformally coated. Batch cleaning machines reduce the risk that a product may be contaminated in some way prior to conformal coating, as it can be cleaned within the process cycle at a negligible cost.
Although “bed-of-nails” test fixture systems are becoming less popular, they are still used by a lot of companies. Most users accept that one cost was replacing spring test pins if they became contaminated by flux residues. Cleaning off flux residues at low cost and within cycle time is now a realistic possibility this makes replacement of pins a mechanical issue and not a chemical one.
Low cost of ownership plus high speed make a potent cocktail and open the doors for products to be cleaned that might otherwise not have been cleaned. They also offer users a much better budget opportunity and the extra cost of cleaning a product can be measured in tiny amounts so that the on-cost to customers is not noticeable even it is applied. We are still faced with hundreds of choices in production but the choice of “clean or not clean” should now be insignificant. Cleaning is here to stay.
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