PCB Technical - PCB circuit board cleaning standards

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 PCB 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.

Table 1. Summary of IPC cleanliness requirements

Standard Residue type Applicable scope Cleanliness standard

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

IPC-6012 Organic matter* All types of electronic solder mask before the light board without 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* Post-weld assembly of class 1 electronics <200μg/cm2

Class 2 electronic post-weld assembly <100μg/cm2

3 types of electronic assembly after welding <40μg/cm2

J-STD-001 Ion* All electronic types of post-weld assembly <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?"

Unlike the “good times” when rosin flux dominated the industry in the past, new surface coatings, fluxes, soldering and cleaning systems are constantly appearing. Obviously, there is no "one-size-fits-all" answer. For this reason, standards and specifications emphasize test procedures used to prove reliability, rather than a simple pass/fail number.

A closer look at the IPC standards-especially IPC-6012, technical indicators and performance of rigid printed boards-reveals that the cleaning of the light board after solder mask, solder or alternative surface coating should be specified in the document Degree requirements. 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 PCB manufacturernot 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. J-STD-001 also has general numerical requirements, as described in Table 1.

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 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.

But is there an easier way? Shorten the detours to increase learning by introducing the experience of others. Such as IPC, EMPF and Naval Avionics Center (US Naval Aviation Center) have conducted a series of tests and industrial studies on various cleanliness conditions; some of these findings are available in the public domain. These technical papers and manuals guide individuals or companies to understand this subtle, but also critical, element of process testing and effectiveness. A good example is the in-depth cleanliness and cleanliness testing program sponsored by IPC, the Environmental Protection Agency (EPA, Environmental Protection Agency), and the Department of Defense (DOD) in the late 1980s. This program investigates new materials and processes used in the cleaning process of PCB manufacturing to reduce the level of chlorofluorocarbon (CFC).

The next big wave in the PCB industry-the movement of lead-free solder and halide-free insulating layers-may trigger another extensive industry-wide study of cleanliness and cleanliness.