Electronics Assembly Knowledge, Vision & Wisdom
Pad Cratering Evaluation of PCBs
Pad Cratering Evaluation of PCBs
This paper reviews major publications and research reports with regard to pad cratering on various PCB materials.
Materials Tech

Authored By:
Dongji Xie, Ph.D.
Dongkai Shangguan, Ph.D.
FLEXTRONICS, San Jose, CA

Helmut Kroener
Multek, Schongau, Germany
,{url:'http://www.circuitinsight.com/videos/programs_final.mp4'}], clip:{autoBuffering:true, autoPlay:true, scaling:'scale' } }).ipad();
Summary
Pad cratering in the PCB is a new failure mode encountered in electronic assemblies, particularly in lead-free products. The failure mechanisms and root causes are not yet fully understood, and lack appropriate industry standard tests for PCB qualification with regard to pad cratering. This paper reviews major publications and research reports on various PCB materials from industry studies in this field. Various PCB tests, such as flexural strength test and pad strength test, have been studied. It is recommended that the qualification of the PCB can be done in two stages: PCB board level and PCBA product level. From those results, a new qualification method is suggested for screening out PCB pad cratering failures
Conclusions
Pad cratering occurs from the cracking of the laminate and/or prepreg materials. Several tests can be used at the PCB materials level, board level, and system level. The flexural strength is not sensitive enough for capturing pad cratering because the prepreg layer normally fails earlier than the core PCB. Three types of board level testing on the pad strength can be used: ball shear, ball pull, and pin pull. Among them, the pin pull test may capture more pad cratering modes than ball shear and pull
tests.

The pin pull test is similar to the peel test for BGA pads and can be used as a good indicator of pad health. The prepreg may crack even if the PCB strain is controlled under 500ue. Solder mask defined pads are preferred in the prevention of pad cratering as it provides more contact area and hereby reduces the stress in the prepreg layer. A new system level PCB qualification process is suggested to mitigate the pad cratering risk. The qualification test uses actual PCBA and simulates multiple reflows and board handling as well as stresses in the field.
Initially Published in the IPC Proceedings
Submit A Comment

Comments are reviewed prior to posting. Please avoid discussion of pricing or recommendations for specific products. You must include your full name to have your comments posted. We will not post your email address.

Your Name


Company


E-mail


Country


Comments


Authentication

Please type the number displayed into the box. If you receive an error, you may need to refresh the page and resubmit the information.



Related Programs
bullet Tacky Substance Under Zero Clearance Parts
bullet Analysis of Laminate Material Properties for Correlation to Pad Cratering
bullet What Causes Black Pad?
bullet Reducing Defects with Embedded Sensing
bullet Can Water Contamination Cause Failure?
bullet Comparison of Solder Paste Residues
bullet Risk and Solution for No-Clean Flux Not Dried Under Components
bullet What is Causing Oxidation?
bullet Hand Sanitizers and Risks to Electronics
bullet What Causes Solder Voids In Leadless Packages?
More Related Programs
About | Advertising | Contact | Directory | Directory Search | Directory Submit | Privacy | Programs | Program Search | Sponsorship | Subscribe | Terms

Circuit Insight
6 Liberty Square #2040, Boston MA 02109 USA

Jeff Ferry, Publisher | Ken Cavallaro, Editor/Business Manager

Copyright © Circuitnet LLC. All rights reserved.
A Circuitnet Media Publication