Surface Insulation Resistance (SIR), as defined by IPC, is the electrical resistance of an insulating material between a pair of contacts, conductors, or grounding devices that is determined under specified environmental and electrical conditions.
In respect to the world of printed circuit boards (PCBs) and printed circuit assemblies (PCAs), SIR testing—also commonly referred to as Temperature Humidity Bias (THB) testing—is used to evaluate a product’s or a process’ ability to resist “failure” by means of current leakage or an electrical short (i.e., dendritic growth). SIR testing is typically performed under elevated temperature and humidity conditions—such as 85°C/85% RH and 40°C/90%—with periodic insulation resistance (IR) measurements obtained.
When developing an SIR testing strategy, the product or process selected for testing will help determine the most appropriate SIR test method as well as determine the most applicable test vehicle. Generally speaking, SIR testing is commonly used to classify, qualify, or compare soldering fluxes and/or cleaning processes. In respect to the latter, SIR testing is commonly used to evaluate one’s “no-clean” soldering operation. The table below summarizes the testing typically involved for each of these categories, as well as the typical sample “type.”
|Product/Process||Test Documentation||Test Coupon|
|Soldering Flux||IPC J-STD-004; IPC-TM-650 methods 184.108.40.206, 220.127.116.11, and 18.104.22.168||IPC-B-24, IPC-B-25A|
|Cleaning or "No-Clean" Processes||IPC-TM-650 method 22.214.171.124||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, mentioned in the table above. This assembly was developed under the guidance of the IPC 5-32b Task Group as a means for more in-depth SIR and Electrochemical Migration study. IPC-9201, known as the SIR Handbook, provides a significant amount of background for SIR testing while IPC-9202 was developed as a guide for using the IPC-B-52 test assembly.
NTS Baltimore has all of the resources and experience necessary to discuss, develop, perform, and interpret SIR testing and its results.
Updated May 07, 2015