Research
Impractical Stencil Aperture Designs to Enable M0201 Assembly
Effectiveness of I/O Stencil Aperture Modifications on BTC Void Reduction
Microalloyed Sn-Cu Pb-Free Solder for High Temp
Selective Reflow Rework Process
Impact of Thermal Loading on the Structural Intergrity of 3D TSV Package
Design and Fabrication of Ultra-Thin Flexible Substrate
Influence of PCB Surface Features on BGA Assembly Yield
Last Will and Testament of the BGA Void
MORE RESEARCH
Latest Industry News
Print These Electronic Circuits Directly Onto Skin
Compal increasingly asked to diversify production bases
Intel's margins tumble as customers shift to cheaper chips, shares slide 10%
From Foldable Phones to Stretchy Screens
6 Considerations for Integrating Sensors in Vehicles
Bill Gates Says Unhappy Customers Are Good for Your Business. Here's Why.
iPhone 12 review: Upgrade for the camera, not 5G
Apple's shifting supply chain creates boomtowns in rural Vietnam
MORE INDUSTRY NEWS

Impact of Assembly Cycles on Copper Wrap Plating



Impact of Assembly Cycles on Copper Wrap Plating
This study quantifies the effects of copper wrap plating thicknesses through IST testing followed by micro sectioning to determine the failure mechanism.
Analysis Lab

DOWNLOAD

Authored By:


Hardeep Heer, Ryan Wong, Bryan Clark - FTG Corporation
Bill Birch, Jason Furlong - PWB Interconnect Solutions Inc.

Summary


The PWB industry needs to complete reliability testing in order to define the minimum copper wrap plating thickness requirement for confirming the reliability of PTH structures. Predicting reliability must ensure that the failure mechanism is demonstrated as a wear-out failure mode because a plating wrap failure is unpredictable. The purpose of this study was to quantify the effects of various copper wrap plating thicknesses through IST testing followed by micro sectioning to determine the failure mechanism and identify the minimum copper wrap thickness required for a reliable PWB.

Minimum copper wrap plating thickness has become an even a bigger concern since designers started designing HDI products with buried vias, microvias and through filled vias all in one design. PWBs go through multiple plating cycles requiring planarization after each plating cycle to keep the surface copper to a manageable thickness for etching.

The companies started a project to study the relationship between Copper wrap plating thickness and via reliability. The project had two phases. This paper will present findings from both Phase 1 and Phase 2.

Conclusions


Phase 1 data analysis showed that as long as there is some copper wrap plating, the main reason for failure was predominantly related to copper plating thickness in the barrel and not copper wrap plated thickness. Typically the failures were a fatigue type of failure. Since no coupon could be found which had no wrap plating at all it could not be categorically concluded that vias with no copper wrap plating would have followed the same failure mode. This led to the Phase 2 study.

The Phase 2 study showed that if coupons had IPC 6012 (C or D) Class 2 and Class 3 copper wrap plating thickness the failure mode would likely be barrel cracking, a fatigue type of failure. This was not true for Class 1 types with no wrap. Through vias with no wrap predominantly had unpredictable (butt joint) types of failure. Some sections also showed fatigue (barrel crack) failures.

This was not true for buried vias. All three types of copper wrap plating thickness coupons for buried vias had an average of 40.0 assembly cycles to failure. Even coupons with no wrap had an average of 31.3 assembly cycles to failure. Almost all failures for buried vias were fatigue related failures.

Weibull chart analysis, resistance plots, IST cycles and micro-sections analysis showed that barrel copper plating thickness has a major influence on cycles to failure rather than the copper wrap plating thickness, PTH via size and cap plating of buried vias.

It was also observed that plated through vias failed earlier compared to buried vias. There could be two factors which could cause the earlier failure. One being the length of barrel and the second being the greater volume of via fill material, which are both affected by z-axis expansion. Lead-free assembly (2450 C) accelerated the time to failure compared to leaded assembly (2300 C).

With a high degree of confidence, it can be stated that a board with Class 2 or greater wrap plating thickness is very reliable and any failure is not likely to be because of copper wrap plating thickness.

Initially Published in the SMTA Proceedings

Comments

No comments have been submitted to date.

Submit A Comment


Comments are reviewed prior to posting. You must include your full name to have your comments posted. We will not post your email address.

Your Name


Your Company
Your E-mail


Your Country
Your Comments



Board Talk
Causes of Blowholes
Tips When Moving a Reflow Oven
Assembling Boards with BGAs on Both Sides
Larger Stencil Apertures and Type 4 Paste
5 vs 8-Zone Ovens
Component Moisture Question?
BGA Components and Coplanarity
How To Verify Cleanliness After Rework and Prior to Re-coating?
MORE BOARD TALK
Ask the Experts
Initial Screen Print Test Board
HASL Surface Finish and Coplanarity
Legend Marking Discoloration
Cleanliness Testing
Stencil Cleaning Frequency
Exposed Copper Risk
Spotting After DI Water Cleaning
ESD Grounding - 1 Meg Ohm Resistor
MORE ASK THE EXPERTS