PCB

Halogen-free PCB Reliability Test and Failure Analysis

The Printed Circuit Board (PCB or PWB) is the base of electronic products. A PCB integrates and connects various electronic components to form a product assembly.

PCB has a history of several decades. In the recent trend of miniature and light-weight electronic products added with promotion of lead-free processes, the assembling temperature of either reflow soldering or wave soldering gets higher, therefore the potential influence resulting from the additional thermal stress against the traditional PCB becomes worse, hence product defects attributed to PCBs also worsen when compared to that before the transfer to lead-free processes. Although material suppliers developed high Tg substrate or improved hardening agents to overcome the thermal stress issue, other problems occurred, e.g., reduced Bond Pad Strength, poor hole-drilling quality, and Conductive Anode Filament (CAF) effect. Therefore PCB Reliability Test once more becomes highly focused.

Apart from the issue of lead-free application, international non-government organizations (NGO) actively promote Halogen Free processes. Meeting requirements of lead-free processes and Halogen limitations, DEKRA has developed a reliability test addressing properties of PCB materials to assist customers in obtaining certificate of preliminary product reliability tests or product sampling analyses.

Temperature Cycling Test and Dynamic Low-Resistance Measurement
Wet/dry Thermal Shock Tests
Electrochemical Migration Test
Copper Trace Tension Test and solder pad bond strength test
Simulation of Heat Resistance Dynamic thermal oil test
CTE and Tg Measurement
Bending Test
Mechanical Shock Test
Failure Analysis

In the past, cross-sectioning is the major resort for the failure analysis of PCBs. When products get thinner and smaller and high-end multi-layer configuration becomes the mainstream, a failure analysis that only relies on cross-sectioning is no longer adequate. In addition, due to lengthy procedures in the PCB production, disputes continued endlessly, arguing whether user-end failures derived from the assembly process or resulted from PCB raw materials.

We apply advanced technologies for analyzing PCB products, such as Focused Ion Beam (FIB) for analyzing micro structures, preventing micro problems from being blurred by the ductile copper material in PCB cross-section process. Auger Electron Spectroscopy (Auger) is used for analyzing existence of trace substances, assisting the customer finding root causes of product defects, it is especially effective for surface analyses. Scanning Electron Microscopy and Energy Dispersive Spectrometer (SEM/EDS) are effective tools for verifying Black Pad causes, minimizing production and assembly risks, and clarifying early failure issues. In addition, equipment including Thermal Mechanical Analyzer (TMA), Atomic Force Microscope (AFM), is very helpful to PCB analyses.

We provide high-tech equipment for carrying out analyses, assisting customers to clarify application problems and implement product improvement solutions. With comprehensive field experiences, we provides customers with various services.

In mid 2009, International Patent Classification (IPC) announced a new verification method 2.6.27 “Thermal Stress, Convection Reflow Assembly Simulation”, which appeared to replace the traditional one - Thermal stress T288. This has been a good news to end users of system, but an extended mishap to PCB suppliers, meaning their products are to face more harsh challenges.

Before the lead free issue in PCBA applications can be fully overcome, international organizations actively begin to promote application development of halogen free PCBs to cope with environmental requirements. This is a further mishap to the PCB industry. PCB attributes enabled evasion of total halogen control issues in the last transfer of RoHS; however the current appeal for halogen free has created more obvious impacts to the industry.

For necessary changes of material properties that cope with the transfer, main problems in halogen free PCBs include hardening and crisping effects, reduced bonding force of copper foil that leads to reduced pad bond strength, pool quality of drill holes due to material hardening, and an increase of wick effects. These problems lead to reduced time of Conductive Anode Filament (CAF), high-frequency instability and Pad Cratering, therefore the design of verification has to make different considerations than the traditional ones, test vehicles must be designed to facilitate product verification. For overcoming Pad Cratering and the Pad bonding strength issue, SMD design overrides NSMD design, which is a totally different approach from the conventional PCB design. Also, PTH pitch and arrangement are key considerations for slowing down the happening of Conductive Anodic Filaments (CAF).

We have developed verification methods for halogen free PCBs, including design of test vehicles, which may be of help to the customer in carrying out preliminary verification of product durability or sampling analysis, assisting the customer to enter into mass production smoothly.