Is Water Good Enough?

When using water to clean assemblies, the question must be asked, “Is water good enough?” The answer to this can affect the end product. Water-soluble fluxes and solder pastes are used because they can be cleaned with water alone. Although with the transition from lead-based solder to lead-free solders, this may no longer be true. Additionally, as pitch and standoff height drop, the physical properties of water make it more challenging to achieve high levels of cleanliness.

The greatest benefit to water-soluble fluxes and solder pastes may be their greatest drawback. The good news is that water is plentiful and has little environmental impact after cleaning. However, if you have chosen water-soluble materials, you must ensure 100 percent removal of the residue. If there are any remaining residues, often they become corrosive, which will damage the assembly. Damage is not the only concern. Yield losses can add significant cost to assemblies, and not meeting reliability demands can cause embarrassment and loss of business. While water seems benign, it can influence a business’ profitability.

While water alone can be sufficient for simple applications, it may not be true for more demanding applications. As advanced packaging and electronics assembly density and complexity increases, the physical properties of water can get in the way of good cleaning. The surface tension of water is 72 dynes/cm and only changes nominally as temperature increases. This can make water difficult to penetrate and to flow under tight standoffs and around tight pitch leads. Once water has permeated the device, it can be difficult to remove. Water can be its own worst enemy. It may be time to consider an alternative.

As assemblers transition from lead-based materials to lead-free materials, the assembly temperatures have increased. This makes the flux residues more difficult to clean. Additionally, the increased flux activation produces added residue and ionic contamination that can affect the throughput, requiring added time to achieve a clean assembly. Some assemblers have found that an engineered cleaning solution can add significant benefit to yield and reliability without impacting profit. These cleaning solutions can be implemented cost effectively with little to no environmental consequence.

These engineered cleaning solutions are added at low concentrations within existing process cleaning equipment. Low concentrations of the cleaning fluid reduces the surface tension to roughly one-third that of water. This increases the ability to clean low standoff and tight pitch assemblies. While designed specifically for high-temperature and lead-free water-soluble fluxes and solder pastes, advanced cleaning materials help improve yield and reliability while maintaining or increasing throughput. Improvements to the bottom line far outweigh the costs of implementing a cleaning solution. So, is water good enough?