Research
Embedded Components from Concept-To-Manufacturing
Copper Foil Elements Affecting Transmission Loss with High Speed Circuits
pH neutral Cleaning Agents - Market Expectation & Field Performance
Reducing Dust Deposition on Electronic Equipment
New Requirements for Sir Measurement
Effects of Mixing Solder Sphere Alloys with Bismuth-Based Pastes
The Development of a 0.3 mm Pitch CSP Assembly Process
Generalizations About Component Flatness at Elevated Temperature
MORE RESEARCH
Latest Industry News
iPhone 12 Production Could Be Delayed
Acer sees PC component shortages
Bio-Ink for 3-D Printing Inside the Body
Covid Seen Driving the Security Sector
U.S. Eases Restrictions on Private Remote-Sensing Satellites
EMS Manufacturing quote complexity drives OEMs to look behind EMS curtain
U.S. Manufacturing Rebounds to 14-Month High
IBM's New AI Tool Parses A Tidal Wave of Coronavirus Research
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
Solder Paste Beyond The Shelf Life?
Issues With Fillets on Via Holes?
Can Tape Residue Contaminate a Clean Tank?
Suggested Stencil Wipe Frequency?
Reflow Oven Zone Separation Challenges
When To Use Adhesive To Bond SMT Components
How To Clean a Vintage Circuit Board Assembly?
PCBA Inspection Concerns
MORE BOARD TALK
Ask the Experts
Lifted Lead on SOT Component
Allowable Bow and Twist on Round PC Fab
Mixed MSL Baking
Step Stencil Squeegee Angle
Solder Balling Splash After Reflow
Application Using No-Clean and Water Soluble Fluxes
IPC SOIC Defect Question
Mixed Process Solder Joint Appearance, Smooth or Grainy?
MORE ASK THE EXPERTS