PGA Substrate Anchoring Elements Pin Tilt Control
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Solution Overview
Problem
Pin tilt failures occur during the flip chip attach process of microelectronic dies to pin grid array (PGA) substrates due to the softening and vaporization of pin-attach solder, especially with lead-free solder metallurgy and NiPdAu surface finishing, leading to weak mechanical and electrical bonds and increased void entrapment.
Innovation Solution
The implementation of anchoring recesses and elements on land pads and pins, respectively, that mate to inhibit tilting, forming a robust pin-attach solder joint by acting as tilt stops, preventing pin movement during reflow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If reflow temperature is reduced to control pin-attach solder softening, then pin tilt is improved, but C4 die attach reliability deteriorates due to insufficient solder joint strength and increased void entrapment
Solution Approach 1:
The patent applies preliminary action by providing anchoring elements on pins and corresponding anchoring recesses on land pads before the reflow process. These anchoring features are pre-configured to mechanically constrain pin movement during subsequent high-temperature reflow, eliminating the need to reduce reflow temperature and allowing C4 die attach to proceed at optimal temperatures without pin tilt issues
Solution Approach 2:
The patent segments the pin structure into distinct functional zones: a pin body for electrical conduction, an anchoring element for mechanical constraint, and a head for solder attachment. This segmentation allows each component to perform its specific function independently, with the anchoring element specifically addressing pin stability without interfering with the C4 die attach process
2Strength
If lead-free SnAg solder is used for C4 bumping, then solder joint strength is improved, but pin-attach solder softening worsens due to overlapping melting ranges
Solution Approach 1:
The patent segments the soldering process into two distinct operations using different solder materials: SnAg solder for C4 bumping (providing strong joints) and SnSb solder for pin attachment (providing thermal stability). This segmentation allows each solder type to be optimized for its specific function without compromise
Solution Approach 2:
The patent applies local quality by specifying different solder compositions for different locations: SnAg solder is used specifically for C4 bumps where high strength is required, while SnSb solder is used for pin attachment where thermal stability and resistance to softening are critical. Each location receives the material property most suited to its functional requirements
3Adaptability or versatility
If pin count and pin density are increased, then package functionality is improved, but pin tilt susceptibility worsens due to lighter and smaller pins
Solution Approach 1:
The patent applies preliminary action by incorporating anchoring elements and recesses into the pin and land pad structures before assembly. This pre-configured mechanical interlocking system provides immediate constraint against pin tilt regardless of pin size or weight, enabling high pin density designs without compromising manufacturing precision
Solution Approach 2:
The patent uses the anchoring element-recess mechanism as a counterbalancing mechanical constraint that opposes the destabilizing effects of reduced pin weight and size. The anchoring features provide a counteracting mechanical force that prevents pin tilt even as pins become smaller and lighter to accommodate higher densities
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Substantially reduces pin tilt and enhances the formation of strong, void-free pin-attach solder joints, improving the mechanical and electrical reliability of PGA connections.
Implementation Method 1
The pins and land pads are provided with mating anchoring elements and anchoring recesses, respectively, that inhibit tilting of the pins on the land pads
Implementation Method 2
The reflow process softens and melts not only the solder bumps on the PGA substrate, but also the solder, such as SnSb, that is typically used to attach the pins of the PGA to lands on the package substrate
Implementation Method 3
During reflow of the solder bumps on the PGA substrate volatile material trapped in the pin-attach solder tends to vaporize
Data Source
AI summary
A microelectronic package substrate and an electrically conductive pin. The substrates includes: a die-side surface adapted to receive a die thereon; a printed circuit board (PCB)-side surface adapted to be mechanically and electrically bonded to a PCB; an array of land pads on the PCB-side surface, the land pads defining anchoring recesses therein; an array of electrically conductive pins electrically and mechanically bonded to respective ones of the land pads, the pins having anchoring elements thereon mated with corresponding ones of the anchoring recesses of the land pads, the anchoring elements and anchoring recesses being configured such that a mating thereof inhibits a tilting of the pins on the land pads; and a plurality of pin-attach solder joints mechanically and electrically bonding the pins to corresponding ones of the land pads.