PCB Fabrication
Ionic contamination is one of the common reasons to PCB assembly failure, which can lead to serious quality issues and huge disaster lost once happen in the mass PCB assembly production.
Sometimes the PCB quality issues is a headache once your expensive printed circuit board not worked as expected. It will bring disaster lost if your expensive boards failed in the mass assembly production even after rigorously verified and tested in prototype process. One of common reasons for circuit board failure is ionic contamination due to it’s exposure to moisture, dust, environment and residues left on the PCB board.
More and more PCBs used in harsh environments, specially in some critical-safety applications such as nuclear energy, requires adequate electron-chemical reliability to control ionic contamination. The PCB production process includes at 20 chemical procedures, most of them involve extensive use of chemical ionic. Generally, contaminants can exist as ionic and non-ionic residues. Non-ionic residues are resin, oils, and grease. They don’t have conductive properties to remain on the printed circuit board surface after PCB assembly. Additionally, ionic contaminants can be organic/inorganic acids, salts, flux activators, and plating chemistries. Therefore, to maintain a high-quality manufacturing process, it is very important to identify and control them.
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Ionic contamination issues usually arise due to the ionic residues from bare printed circuit board production or from the chemical materials used in PCB assembly process. These residues can exist as various of substances including plastic, metal, and fiberglass granules, salts, oils, moisture, and dust. These ionic residues have a zero net charge (the composition of negative anions and positive cations) and get charged when a bare printed circuit board passes through multiple production processes. While in PCB assembly process, the electronic components also possibly carry various ionic/conductive contaminants along with fluids, biocides, and corrosion preventatives, etc. The treatment of the circuit board in the production process is also a major cause of ionic contamination in a bare printed circuit board.
Chemical etching and plating in PCB etching process are highly conductive and corrosive. It must be neutralized or rinsed them as they are a potential cause of leakage current.
Commonly, the conductive flux residues from the soldering process include various binders, unreacted activators, saponifiers, and rheology elements. To avoid the potential risk of PCBA lifetime, these residues must be thoroughly removed by using solvent cleaning, say vapor degreasing, or by aqueous chemistries in the common batch.
Before assembling the components on the bard printed circuit boards, you need to ensure no contaminants left from operation process.
These must be removed to ensure non contaminants left on the circuit boards
A family of chemicals that work as surfactants and emulsifying ingredients in cleaning PCB assemblies.
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In all PCB failure cases, approximately 15% of these occur due to contamination issues. In the PCB manufacturing process, the bare PCB can carry ionic contaminants in the form of left-over flux, etching chemical, and solder material. Once these residues remaining on the board, some major issues such as Electrochemical Migration (ECM), corroded traces, parasitic leakages, and dendritic growth, can directly have impacts on the printed circuit boards life-cycle.
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Electrochemical migration commonly occurs in the electric field in which metal gets dissolved, resulting in ion formation between two copper conductors. Once the electric field is applied, the metal dissolves at the Anode and gets deposited to the Cathode resulting in the growth of dendritic structures between anode and cathode. Because dendrites grow from conductive ions, they can misdirect PCB currents from what should be, leading to short circuits. Dendrites create alternative current paths that can affect the accuracy of current measurements in a printed circuit board.
Commonly, bare printed circuit boards corrode due to its material. Ionic contamination can expedite the corrosion of a PCB. When the ionic residue get in contacts with moisture, the short-circuit risk increases. The corroding metal falling off, need to know more about the chemical properties to have the operation correctly.
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Don’t hesitate, contact us to start discussing your projects. We prioritize your inquiries and aim to respond within 12 hours.
Bad quality control and poor production process during PCB manufacturing, components assembly, and a substandard final cleaning are some of the major issues that lead to ionic contamination. It is critical to identify, control and avoid this issues. It can be done through proper ionic contamination testing and analysis via specific equipment. Typically, some well-known methods such as ROSE testing, ion extraction,and ion chromatography can do this well. Usually, it is necessary and worth to do humility validation testing at the beginning of the production.
