Authored By:
Andrew Mawer, Mollie Benson, X.S. Pang,
Stephen Lee, J.Z. Yao and Alvin Youngblood
NXP Semiconductor
Austin, Texas USA
Summary
Plastic Leaded Chip Carrier (PLCC’s) packages with J leads were developed during the time of widespread adoption of surface mount technology (SMT) in the 1980’s [1]. By the 1990’s, Quad Flat Pack (QFP) packages with gull wing leads had become the mainstream SMT packaging technology for products with pin counts ranging from 40 to 200 plus leads [2]. Many improvements have been made to QFP’s over the decades including increased thermal performance with bottomside exposed pads and other enhancements, automotive reliability with MSL3 performance, stacked die, lead pitch decreases down to 0.4 mm and even 0.3 mm and pin counts as high as 304.
This paper will discuss a novel QFP package called the MaxQFP [3-8] which combines the J leads of a PLCC with the gull wing leads of the traditional QFP within the same package to result in a cost-effective solution with roughly twice the IO density of a standard QFP at a given body size. The MaxQFP package also provides the cost benefits of a leadframe based package on products that would normally be packaged in a plastic BGA. Typically, a singular MaxQFP leadframe design can be used to accommodate multiple SoC designs. The package construction and some of the unique component assembly challenges will be discussed, but the paper will focus primarily on all aspects of SMT assembly of the MaxQFP. Additionally, the robustness of the assembly in automotive type board-level thermal cycling will be demonstrated.
Conclusions
The following can be concluded as a result of this MaxQFP package development effort and associated assembly and reliability evaluations:
- A novel and evolutionally package was developed that combines the J-leads of a PLCC and the gullwing leads of a conventional QFP to greatly increase IO density.
- Besides being a potential replacement for conventional QFP where increased density and/or smaller form factor are required, MaxQFP may also provide an acceptable and more economical packaging solution than BGA at lower lead counts.
- MaxQFP has been demonstrated to meet or exceed AEC Grade 1 component-level reliability requirements including the additional requirements placed upon Cu wirebond devices.
- SMT studies showed that excellent soldering yields and robust solder joints could be achieved. Three different PCB pad geometries were evaluated and all resulted in 100% SMT yield. A PCB pad geometry where the gullwing and J-lead pads were both 1.45×0.28 mm resulted in the best cycles to first failure.
- Future extensions of the technology may include an exposed pad for better thermal performance, finer pitches including 0.5 mm and additional body sizes than the 10×10 and 16×16 mm that have been implemented to date.
Initially Published in the SMTA Proceedings
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