Coreless technology in package substrate has been developed to satisfy the increasing demand of lighter,smaller and superior electrical performance regarding as the future trend in electronic application. However,there are major challenges of reducing coreless substrate warpage in terms of both substrate manufacturing and assembly process. Substrate manufactures typically provide substrate warpage within satisfying customer’s specification which does not allow much margin left in assembly considering the number of reflows and curing profiles which the package undergoes during assembly. However,it is very difficult to provide satisfying this level of warpage because coreless substrate is one-third as thin as conventional one and does not use stiff core material. The key element for success in coreless technology is to solve the warpage issue at manufacturing site because the decrease of bare substrate warpage is important to improve the assembly yield. To figure out these problems,design optimization,mechanical/thermal treatment and low CTE material are suggested in this study. Final part discusses assembly result and issue for future work.

Due to the obsolescence of SnPb BGA components,electronics manufacturers that use SnPb solder paste either have to use
lead-free BGAs and adjust the reflow process or re-ball these components with SnPb balls. The reliability of Lead-Free and
Lead-Containing solder joints for BGA’s has been investigated after re-balling using optimal microscopy. The goal was to compare the quality of the connections for both options. For the lead-free BGA,voids produced by the release of volatile species in flux during soldering were present. Large voids have been observed at the interface component/solder. Using components that were re-balled did not show the amount of voiding observed for the lead-free BGA. Kirkendall voiding has been observed for the lead-free component at the component/solder interface. It has been therefore concluded that the use of the reballed components is to be preferred to adjusting the reflow profile and using lead-free components.

Accelerated temperature cycling was used to evaluate the thermal fatigue reliability for the case of backward compatible
assembly (mixed alloy,Pb-free BGA/SnPb paste) of a 3162 pin count,extremely large body (51.0 mm x 59.5 mm) ball grid
array (BGA). The BGA component was fabricated with Sn-4.0Ag-0.5Cu (SAC 405) Pb-free solder balls and surface mount
assembly was done using SnPb eutectic soldering profiles. The profiles were selected to simulate situations involving
incomplete mixing in order to study the effect of various levels of Pb mixing and microstructure on solder joint quality and
thermal fatigue reliability. Although the most common criteria for acceptable mixed alloy assembly are uniform or 100% Pb
mixing throughout the solder joint and complete ball collapse during reflow,these criteria can be difficult to meet with larger
BGA packages due to thermal issues. The effect of such imperfect mixing on reliability of large packages is unknown. The
test program included Pb-free,SAC405 assemblies to provide a reliability baseline comparison. Testing was done using a 0
to 100 ?C temperature cycle with 10 minute ramp and dwell times and post-cycling failure analysis was conducted on
representative test samples. Baseline characterization and failure analysis included optical metallography and scanning
electron microscopy (SEM). The thermal cycling test data and failure analysis results are discussed in terms of the
relationship to the initial as well as evolving Pb-free and mixed alloy microstructures. The reliability data indicate that mixed
assemblies can provide acceptable reliability,even in some cases when Pb mixing is not complete or uniform. However,
these results also show that warpage effects can increase the operating risk by reducing the process margin. Further,it is
shown also that the reliability likely is influenced more by the underlying Pb-free microstructure than by the Pb introduced
by mixed assembly.

Commercial-off-the-shelf ball/column grid array packaging (COTS BGA/CGA) technologies in high reliability versions are now being considered for use in a number of National Aeronautics and Space Administration (NASA) electronic systems. Understanding the process and quality assurance (QA) indicators for reliability are important for low-risk insertion of these advanced electronic packages. This talk briefly discusses an overview of packaging trends for area array packages from wire bond to flip-chip ball grid array (FCBGA) as well as column grid array (CGA). It then presents test data including manufacturing and assembly board-level reliability for FCBGA packages with 1704 I/Os and 1-mm pitch,fine pitch BGA (FPBGA) with 432 I/Os and 0.4-mm pitch,and PBGA with 676 I/Os and 1.0-mm pitch packages.

- What is Pad Cratering?
- Pad Craters
- Pad Cratering… Opens Circuits
- How is the Electronics Industry dealing with this Defect Mode?
- What does this have in common with a Pad Cratering solution?
- Film Based Materials
- Material developments that are addressing Pad Cratering
- Examples of Fractures
- Fracture Barrier

Electronics assemblies with large flip-chip BGA packages can be prone to either pad cratering or brittle intermetallic (IMC)
failures under excessive PCB bending. Pad cratering cracks are not detected by electrical testing or non-destructive inspection
methods,yet they pose a long term reliability risk since the cracks may propagate under subsequent loads to cause electrical
failure. Since the initiation of pad cratering does not result in an instantaneous electrical signature,detecting the onset of this
failure has been challenging. An acoustic emission methodology was recently developed by the authors to detect the onset of
pad cratering [1,2]. The instantaneous release of elastic energy associated with the initiation of an internal crack,i.e.,
Acoustic Emission (AE),can be monitored to accurately determine the onset of both pad cratering and brittle intermetallic
(IMC) failures.
In this study,the AE technique is used to systematically investigate pad cratering in a daisy chain 40 x 40 mm Flip-Chip
BGA (FCBGA) package with lead-free SAC305 solder balls and 1 mm ball pitch. AE sensors have been attached to a fourpoint
bend test vehicle to determine the onset of either pad cratering or brittle IMC failures. A two-dimensional AE source
location method has been used to determine the planar location of failures on the test board. The test matrix is designed to
investigate the effects of normal or diagonal strain orientation,NSMD or SMD PCB pads,and single or multiple reflow
cycles. Physical failure analysis has been performed to correlate the test results with failure modes.

The increased temperatures associated with lead free processes have produced significant challenges for PWB laminates.
Newly developed laminates have different curing processes,are commonly filled with ceramic particles or micro-clays and
can have higher Tg values. These changes designed to reduce Z-axis expansion and improve the materials resistance to
thermal excursions through primary attach and rework operations have also produced harder resin systems with reduced
fracture toughness.
Celestica has undertaken an extensive “Spherical Bend Test” program to assess lead (Pb) free compatible materials and area
array packages. This work has confirmed “Pad crater / Pad Lift” as the dominant failure mode in Pb-free materials in
agreement with observations from multiple streams of field returned product. This work discusses the multiple phases of
testing and the implications for mechanical reliability of Pb-free product. The initial phase was designed to confirm or refute
the established relationship between strain rate and safe working strain in Pb-free materials. The second phase studied the
effect of extended thermal excursions for an extensively used standard loss laminate material. The third phase was designed
to directly compare standard loss laminate materials and has confirmed the impact of filled resin systems identified by other
investigators
This new work seems to confirm the relationship between board thickness and safe working strain established by in
IPC/JEDEC-9704: “Printed Wiring Board Strain Gage Test Publication”. Data is only available for a limited number of
package designs but these selected packages are believed to generate conservative strain limits for manufacturing process
guidelines. The design of the most recent test plan was intended to generate data that would allow investigators to generalize
the effect of package compliance on the safe working strain of the assembly by correlation of test data from multiple
packages to an existing simplified mechanical model.
Assembly processing,test methods and results will be documented in addition to discussion on resultant data,failure
analysis,distribution parameters. The effectiveness and predictive range possible from the simplified model will also be
discussed.

As technology advances,understanding thermal management issues of high frequency PCB’s increases. There are many different aspects to consider for PCB thermal management. This paper will investigate thermal management issues of high
frequency PCB’s as it relates to material properties,insertion loss and circuit design configurations. It will be shown that
there are many tradeoffs between these aspects which can be very beneficial for the circuit designer to be aware of.

With the emergence of high speed,controlled impedance circuits requiring increasingly tight tolerances,there is a realization among designers and fabricators that more precise data is needed than the normal “data sheet” information given by materials companies. To meet this need,an extensive study has been conducted over the past year to closely evaluate flexible circuits in “real world” transmission line structures. The outputs of this study are clearly understood impedance and loss data that can be used as a basis for designs and fabricated structures.
The following structures will be evaluated:
-Microstrip Lines
-Covered Microstrip Lines
-Microstrip Lines with ENIG Finish
The following materials will be evaluated:
-Standard FR4 (100 um thick),Mid-Grade Glass Reinforced Epoxy (100 um and 50 um thick) and Low Loss Rigid Glass Reinforced Epoxy (100 um and 56 um thick)
-Adhesiveless Polyimide (50 um and 100 um thick)
-Fluoropolymer/Polyimide Composite (50 um,75 um and 100 um thick)
Loss will be evaluated in terms of loss per unit length versus frequency at frequencies between 0.2 GHz to 25 GHz for long lengths. Impedance is measured utilizing typical TDR systems used by fabricators and compared to commercially available impedance calculation systems.

Creep corrosion normally happens in the end system,PCB,connectors and components are widely noted due to the exposure of
high sulfur environments under elevated humidity. In this study,the major focus is the investigation of PCBs with 3 different
types of surface finish (ImAg,Post-Treatment ImAg,HT-OSP),SMD vs NSMD and non clean organic acid flux residue from
simulating wave soldering process under MFG Test (Mixed Flowing Gas Test). The realistic mixed flowing gas (H2S,SO2,NO2,
Cl2) at certain concentration of each and relative humidity are designed to accelerate creep corrosion happening.
One of the purposes in this study is to investigate the effect of the mixed flowing gas with various H2S concentration (500 ppb,
1000 ppb,1700 ppb) at 5 days duration on the corrosion rate (nm/day) in the Cu coupon and Ag coupon in order to understand
how H2S drives the corrosion acceleration. The data are also verified by the methods of Weight Gain Analysis and X-Section
with SEM/EDX.
The result shows much higher corrosion rates are observed on Cu coupon in both Individual and Mixed Flowing Gas Tests. The
corrosion rate of Cu coupon rapidly increases with H2S concentration above 1000 ppb. Ag coupon have more active corrosion in
low H2S concentration than high H2S concentration. Flaking corrosion also happens on the Cu coupon with heavy corrosion
product in the high H2S concentration test condition. And more visible creep corrosion is observed on HT-OSP finished circuit
boards and SMD,as the residue of organic acid flux residue is not able to prevent corrosion occurrence.