At Rush PCB Inc., we understand the importance of keeping the circuit board clean during the assembly processes, and effectively cleaning it again at the end. Usually, PCB assemblies collect various contaminants during the production process, and if the assembly line does not take proper care of cleaning, the contaminants could impact the ability of the board to function as intended.
Although PCB manufacturers follow various industry standards, Rush PCB Inc. prefers to follow international standards such as IPC-A-610 and IPC Test Methods 650 for ensuring proper cleanliness of our customers’ boards. As a contract manufacturer, we have the necessary processes in place for inspecting and cleaning assembled boards. Here, we would like to explain why cleanliness is important, and why we insist on PCB cleanliness at all stages.
Why is PCB Cleanliness so Important?
Fabrication takes the circuit board through several processes, starting from etching of copper to the deposition of solder paste during assembly. We use various chemicals during these processes, and all of them have the potential of leaving different residues and contaminants on the surface of the board. Several short-term and long-term problems may result from these residues and contaminants.
Short-Term Issues: poor aesthetics is the main short-term issue that residues and contaminants exhibit. While they may not actually cause damage to the assembly, their obviously visible presence raises concerns. For instance, no-clean flux leaves visible residues that, by themselves, are harmless, but the board nevertheless looks very unclean.
There are cleanable fluxes, and they leave residue on the board, which, if not cleaned properly, can cause problems later, such as during testing. Some contaminants can also cause functional problems of intermittent nature, which may be difficult to trace or reproduce.
Long-Term Issues: inadequate cleaning can cause long-term issues and these are a larger threat. Uncleaned residues and contaminants can reduce the reliability of the completed assembly.
For instance, ionic contamination, if not cleaned thoroughly, may turn conductive in the presence of moisture. This can lead to dendritic growth of conductive metallic slivers causing possible electrical short-circuit between traces. Another effect of these conductive molecules is they accelerate corrosion.
Several types of ionic residues may collect on a PCB during various manufacturing processes. These include:
- Perspiration acids
- Etching acids
- Plating chemicals
- Flux activators
- Various salts
Inadequate cleaning can lead to poor adhesion of conformal coatings, causing long-term environmental issues. Board mounted switches and relays may start to malfunction and sockets, edge connector fingers, and cable connectors may start to exhibit issues of intermittent connections. These are only a few of the problems why Rush PCB Inc. insists on cleanliness in all our manufacturing processes.
Cleaning PCB Assemblies and Testing Them
With shrinking conductor widths and spacing, ionic contamination propagating dendritic growth is becoming an increasing risk. In general, for military boards, we abide by the universal specification of maintaining contamination levels below 10.06 µg/in2 or 1.56 µg/cm2 of Sodium Chloride. However, this is true for production panels before we have applied the solder mask. The reason is higher levels of ionic contamination may remain entrapped below the solder mask, eventually affecting solder mask adhesion, causing blistering, voiding, and ultimately leading to peeling-off of the solder mask.
At Rush PCB Inc., we clean boards in-line with warm jets of deionized or DI water. For setting the water pressure we follow guidelines from solder and equipment manufacturers. Depending on the type of contaminants, we may also use additional cleaning processes such as wiping with isopropanol or IPA, and ultrasonic cleaning for removing no-clean flux residues. We follow documented requests from our customers for more specialized cleanings.
To ensure that cleaning is adequate, we regularly test our processes. Initially we inspect the finished assembly to ensure it passes our internal standards. Periodically, we submit samples for testing to a third-party service provider, for which we use the standard resistivity of solvent extract or ROSE test, conforming to IPC 6012.
To assure our customers that we thoroughly clean their boards, Rush PCB Inc. claims the following:
- We have a company culture promoting attention to detail, and we possess and use a facility for cleaning during our operations.
- We have a long experience of conforming to PCB manufacturing cleanliness standards.
- We use proper equipment and processes for adequately cleaning circuit boards.
- We can use several specialized cleaning processes, depending on the customers’ requests.
Cleanliness Standards for Unpopulated Boards
We follow the standard IPC-5704 for cleanliness of unpopulated boards. For this, we resort to Ion Chromatography testing. However, this is an expensive test and we conduct this test against specific requests from customers only for boards such as those necessary for medical electronics and the aerospace industry.
Rush PCB Inc. always puts quality and reliability before everything else, and this includes proper cleaning of circuit boards during assembly. Our certification includes ISO9001, and we have top-level equipment and fully documented processes for cleaning. Furthermore, our cleanliness procedures confirm to international standards. We confirm our commitment to the highest level of quality for our customers.