Electronics Assembly Knowledge, Vision & Wisdom
Mechanical Shock and Drop Reliability Evaluation of the BGA Solder Joint Stack-Ups
Mechanical Shock and Drop Reliability Evaluation of the BGA Solder Joint Stack-Ups
This paper investigates the Mechanical Shock and Drop Reliability of SnAgCu ball Flip Chip BGA solder joints.
Production Floor

Authored By:
Olivia H. Chen and Al Molina
Intel Corporation
Folsom, CA, USA

Raiyo Aspandiar, Kevin Byrd, and Scott Mokler
Intel Corporation
Hillsboro, OR, USA

Kok Kwan Tang
Intel Corporation
Kulim, Malaysia
,{url:'http://www.circuitinsight.com/videos/programs_final.mp4'}], clip:{autoBuffering:true, autoPlay:true, scaling:'scale' } }).ipad();
Summary
Printed circuit boards (PCB) used in the consumer electronic products such as smart phones, tablets and mobile client personal computers are commonly assembled by reflow soldering with lead-free SnAgCu (SAC) solder pastes with peak relow temperature in the 240C to 260C ranges. However, due to the decreasing size of electronic devices which demands lower z-height stackup, the ultra-thin flip chip ball grid array (FCBGA) often experienced SMT soldering challenges with typical lead-free solder reflow due to dynamic warpage on package substrate and PCB.

As a result, low temperature solder pastes of the Bi-Sn metallurgical system have been proposed as alternatives to SnAgCu solder pastes for assembly of boards in the mobile consumer electronics market segments. Besides improvements in solder joint yield due to lower package and board warpages at the peak reflow temperatures, the lower melting points of these solder pastes will also enable significant cost savings.

However, presence of significant amounts of Bi in Sn based solder has previously been shown to induce embrittlement in the solder joints which leads to lower mechanical shock resistance. Hence, solder pastes, containing resin, have been developed recently to provide a post reflow polymeric reinforcement encapsulation around the mixed BiSn+SnAgCu BGA solder joints to mitigate this risk by enhancing the shock reliability of these solder joints.

This paper will investigate the Mechanical Shock and Drop Reliability of SnAgCu ball Flip Chip BGA solder joints soldered with BiSnAg (BSA), and Resin Reinforced BiSn system solder pastes (termed Joint Reinforced Pastes, JRP). This data will be compared to that obtained for SnAgCu ball Flip Chip BGA solder joints soldered with standard SAC solder paste, with and without board level adhesive reinforcement.

Reflow processing conditions, the solder joint shape, microstructure, morphology and failure modes, for each of these cases, will also be described and discussed. Based on in-situ failures recorded during shock event, JRP and SAC305 showed comparable performance, while BSA showed lowest number of drops to failure (less shock resistant). BSA leg showed more failure propagation on additional package locations while SAC305 and JRP legs did not show additional failures at other package locations other than the first two rows of solder joints from the package corners.

In summary, BSA shock margin was significantly improved after the addition of L-shaped corner glue on all four package corners. No failures were seen on the BSA+CG leg. Hence board level adhesive and polymeric joint reinforce pastes, JRP both showed promising result to mitigate shock margin loss due to the brittle nature of BSA paste.
Conclusions
The brittleness of Bi-Sn alloys, even after addition of Ag to the system, limits its use in consumer products where the risk of multiple shock impacts is high. Resin reinforcement solder pastes have been developed recently to provide a polymeric reinforcement around the mixed BiSn+SnAgCu BGA solder joints to mitigate the risk of embrittlement in Bi-Sn solder joints in order to enhance shock reliability.

In summary:

Based on in-situ failures recorded during shock event, JRP and SAC305 showed comparable performance, while BSA showed lowest number of drops to failure (less shock resistant).

BSA leg showed more failure propagation on additional package locations while SAC305 and JRP legs did not show additional failures at other package locations other than the first two rows of solder joints from the package corners.

BSA shock margin was significantly improved after the addition of L-shaped corner glue on all four package corners. No failures were seen on the BSA+CG leg, outperforming both the SAC305 and JRP legs.
Initially Published in the SMTA 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 attempt to submit information and receive an error, you may need to refresh the page and insert the information again.



Related Programs
bullet Drop Test Performance of BGA Assemblies
bullet Expanding IEEE Std 1149.1 Boundary-Scan Architecture
bullet Analysis of Voiding Under QFN Packages
bullet Effective Test-Probe Assignment
bullet A Packaging Physics of Failure Based Testing Methodology
bullet TDI Imaging: An Efficient AOI and AXI Tool
bullet On-Board Package Decapsulation Techniques for Failure Analysis
bullet Tools and Techniques for Material Assessment in Advanced Technologies
bullet Mechanical Shock and Drop Reliability Evaluation of the BGA Solder Joint Stack-Ups
bullet PCBA Inspection Concerns
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