PCB News - Standards for PCB circuit board cleaning

A question often asked through our technical support hotline is, "What is the IPC standard for cleanliness?". This is a simple and straightforward question often asked by novices in the industry, so a simple and straightforward answer is generally what they want. However, in most cases, this is not professional enough for their personal needs.

In order to answer this question, we must first understand the simple standards: IPC standards being used, types of residues, scope of application and cleanliness standards. Table 1 answers these questions, the old way-fast and simple.

Standard Residue type Applicable scope Cleanliness standard

IPC-6012 Ion All types of electronic solder mask before coating <1.56μg/cm2NaCl equivalent

IPC-6012 Organics* All types of electronic solder mask before the light board No contaminant precipitation

J-STD-001 All types, all types of electronic solder mask before the light board, enough to ensure solderability

J-STD-001 Granules All electronic types of post-weld assembly non-loosing, non-volatile, minimum electrical separation

J-STD-001 Rosin* Class 1 electronic post-weld assembly <200μg/cm2

Post-weld assembly of class 2 electronics <100μg/cm2

Post-weld assembly of class 3 electronics <40μg/cm2

J-STD-001 Ion* Post-weld assembly of all electronic categories <1.56μg/cm2NaCl equivalent

IPC-A-160 Visible residues Post-weld assembly of all electronic categories Visual acceptability

* When testing is required

But do these answers provide the necessary facts? Unfortunately, the caller is rarely satisfied. In fact, these answers usually lead to more questions, such as: "Is it this?"; "What if the contaminants have more chlorides?"; "What about flux residues in the no-clean process?" ; "What if I use a conformal coat to protect the assembly?"; Or, "What about other non-ionic contaminants?"

A closer look at the IPC standards-especially IPC-6012, Technical Specifications and Performance of Rigid Printed Boards-reveals that the cleanliness of the light board after solder mask, solder or alternative surface coating should be specified in the document Require. This means that the assembly manufacturer must tell the circuit board manufacturer how clean they want the bare board. It also leaves room for assembly manufacturers using no-clean processes to impose stricter cleanliness requirements on incoming circuit boards.

The assembly manufacturer not only needs to specify the cleanliness of the incoming board, but also agrees with the user on the cleanliness of the assembled product. According to J-STD-001, unless specified by the user, the manufacturer should specify cleaning requirements (either no-washing or one or two assembly surfaces to be cleaned) and test cleanliness (or not requiring testing, surface insulation resistance testing, or testing ion, Rosin or other organic surface contaminants). Then the cleaning system is selected on the basis of the compatibility of the welding process and the product. The cleanliness test will depend on the flux and cleaning chemicals used. If rosin flux is used, J-STD-001 provides digital standards for products of 1, 2, and 3. Otherwise, the ion contamination test is the simplest and least costly.

If chloride content is a concern, industrial research results involving ion chromatography have shown that the following guidelines are reasonable breakpoints for chloride content. When the chloride content exceeds the following levels, the risk of electrolysis failure is increased:

For low solid flux, less than 0.39μg/cm2

For high solid rosin flux, less than 0.70μg/cm2

For water-soluble flux, less than 0.75-0.78μg/cm2

For tin/lead metallized light board, less than 0.31μg/cm2

Discussions on cleaning often come to this final answer: The true cleanliness of PCBs depends on the product and the desired end-use environment. But how do you decide what cleaning is sufficient for a specific end-use environment? Through thorough and rigorous analysis, each potential pollutant and end use situation are studied, and long-term reliability testing is carried out.