The Surface Insulation Resistance (SIR) defined by IPC is the electrical resistance between an insulating material, a pair of contacts, conductors or grounding devices specified under specified environmental and electrical conditions.
In the world of printed circuit boards (PCBs) and printed circuit assemblies (PCAs), the SIR test, also called the Temperature Humidity Tendency (THB) test, is commonly used to evaluate the resisting ability of a product or process. SIR testing is typically performed under elevated temperature and humidity conditions (eg 85 ° C / 85% Relative Humidity and 40 ° C / 90%) with the periodic insulation resistance (IR) measurements obtained.
While developing an SIR test strategy, the product or process selected for the test will help determine the most appropriate SIR test method and determine the most appropriate test tool. Generally speaking, the SIR test is commonly used to classify, qualify or compare solder fluxes or cleaning processes.
Regarding the latter, the SIR test is often used to evaluate the “clean” soldering process. The table below summarizes the tests typically performed for each of these categories and the typical sample “type”.
| PRODUCT / PROCESS | TEST DOCUMENTS | TEST COUPON |
| Soldering Flux | IPC J-STD-004; IPC-TM-650 methods 2.6.3.3, 2.6.3.6 and 2.6.3.7 | IPC-B-24, IPC-B-25A |
| Cleaning or "No-Clean" Processes | IPC-TM-650 method 2.6.3.7 | IPC-B-36, IPC-B-52 |
The idea of SIR testing has progressed in recent years with the development of the IPC-B-52 assembly specified in the table above. This assembly was developed as a tool for the in-depth SIR and Electrochemical Migration study under the guidance of the IPC 5-32b Task Group. IPC-9201, known as the SIR Handbook, provides a substantial background for the SIR test, while IPC-9202 was developed as a guide for the use of the IPC-B-52 test setup.
As the gap and part sizes decrease in PCBs, the need to validate Conductive Anodic Filament (CAF), Surface Insulation Resistance (SIR) and Electrochemical Migration Resistance (ECM / EMR) has steadily increased. These tests use high temperature / humidity environments to understand the reliability of a product by speeding up faults that may occur. The electrical properties are evaluated during or after accelerated environmental exposures to further determine the performance of the product under these severe conditions.
Conductive Anodic Filament (CAF) its formation is a well-studied phenomenon, guided by chemical, humidity, voltage and mechanical means. It is characterized by a sudden loss of insulation resistance occurring internally in the PCB. CAF dendrites can occur between adjacent Plate Holes (PTH) or between a plate hole and a line on the PCB. Coating chemistry, material consistency, damage caused by multiple soldering steps, and overvoltages (beyond designed stresses) accelerate the start of the CAF. The CAF mechanism is the electrochemical transport of ions along the electrical potential between the anode and cathode.
Surface Insulation Resistance (SIR) testIt is a methodology used to characterize PCB manufacturing and electronic assembly process residues and their impact on reliability. It is usually performed in industry standard test board coupons containing models, typically interlocking comb test patterns designed for process testing. Patterns are exposed to a high humidity environment that contaminates any surface and reduces the insulation resistance of the test pattern.
Applying a new assembly process step or chemistry can damage the end product performance. The new IPC-9202 is designed to help verify and record the effects of new processes on surface insulation resistance (SIR). Residues left on the boards after assembly may cause contamination and corrosion, which can affect the long-term reliability of the assembly.
EUROLAB provides the highest Surface Insulation Resistance (SIR) test available today. For the new IPC-9202 standard, our tests use the IPC-B-52 test tool, which is intended to represent electronic circuits in your production.
Reporting through industry best practices, test methods and active participation and our leadership, EUROLAB's expert team helps create standards, processes and test methods for IPC-9202, which provides both quantitative and qualitative data. EUROLAB's SIR / CAF and ECM testing ensures your assemblies meet new standards.
Electrochemical Migration Resistance (ECM / EMR) is the transport of surface materials resulting from the gradual movement of ions in a conductor due to the momentum transfer between conductive electrons and diffused metal atoms. The effect is important in applications where high direct current densities are used, such as microelectronics and related structures. As the structure size in electronics decreases, the practical significance of this effect increases. Electrochemical Migration reduces reliability electronics by causing the circuit's high resistance shorts. In the worst case, it leads to the eventual loss of one or more connections and intermittent malfunction of the entire circuit. The reliability of interconnections is of great interest not only in the field of space travel and for military purposes, but also in civilian applications such as the vehicle's anti-lock braking system and telecommunications.
EUROLAB has years of experience in Environmental Simulation and Accelerated Life tests, including CAF, SIR and ECM / EMR tests, and can help you understand the reliability and performance of your product. EUROLAB provides the fastest possible return and the highest level of technical support to test your products. Using the latest technology, EUROLAB has the technical expertise to meet your most demanding test requirements, and BELLCORE GR-78-CORE can test in military and commercial applications such as specific customer standards and IPC test methods.
The AUTO-SIR System measures insulation resistance typically during test coupons during artificially elevated temperature and humidity cycles. The purpose of SIR, CAF and ECM testing is to capture dangerous trends for malfunction mechanisms such as unacceptable electrical leakage, corrosion or metal migration under humid conditions.
EUROLAB has all the necessary resources and experience to discuss, develop, perform and interpret the SIR test and its results.
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