Mechanical Enabling for the Intel® Pentium® 4 Processor in the 478-Pin Package October 2001 Order Number: 290728-001 Copyright © 2001, Intel Corporation 1
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Table of Content Mechanical Enabling Reference Design Overview Critical Mechanical Design Requirements Design Effectiveness 3
Reference Design Overview Mechanical Enabling Reference Design is: Intel-developed enabling solution for the Intel® Pentium® 4 processor in the 478-pin package and the Intel® 845 MCH Developed for general industry use Targeted at low-cost, high volume manufacturing & integration approach 4
Reference Design Overview Full Assembly Processor Fan Housing Processor Clip MCH Heatsink Processor Heatsink MCH Clip Processor Retention Mechanism (RM) 5
Critical Design Requirements Power Dissipation Traditionally the driving design requirement Mechanical Retention Strongly impacted by power dissipation requirements Has gained importance with increasing heatsink mass 6
Critical Design Requirements Mechanical Requirements Withstand environmental load conditions 50g board-level mechanical shock 3.
Critical Design Requirements Design Challenges During shock and vibration events: Avoid processor package pull-out Protect against processor socket solder joint damage Protect against MCH solder joint damage Prevent Thermal Interface Material (TIM) thermal performance degradation Allow chassis-independent solution 8
Engineering Strategy Compressive Preload Induced through cam rotation Helps protect against package pull-out and solder joint damage Improves thermal performance Clip Lever (with cam) Clip Frame Motherboard (MB) Surface Mount Component Lever Fully Engaged For additional information on Reference Solution Assembly, see reference [6] slide 25.
Reference Design Overview Intel® Pentium® 4 Processor in the 478-Pin Package Enabling Assembly Clip Fan/Housing Provides clip bearing surface and load transfer to heatsink Comes pre-assembled to clip Heat sink Generates preload Comprised of frame and mechanical advantage levers Carries preload through fins to processor Retention Mechanism Engages clip hooks through windows Attaches to board with Tuflok* fasteners Note: The weight of the Intel Reference Solution is approxi
Reference Design Overview Intel® 845 MCH Enabling Assembly Clip Lever Clip Frame Generates preload Engages with clip frame Point contact to heatsink, centered on die Carries preload to board Attaches to board using throughhole mount anchors Maintains heatsink position on die Heatsink Distribute the load evenly onto the die 11
Design Effectiveness How does the Intel reference design meet these challenges? Avoid processor package pull-out Avoid socket solder joint damage Avoid MCH solder joint damage Prevent TIM (thermal interface material) thermal performance degradation Allow chassis-independent solution 12
Design Effectiveness Processor Package Pull-Out - 1 Both vertical and lateral shock conditions can produce pull-out Pull-out occurs when heatsink moves up or shifts laterally excessively during shock Primary factors Clip Load Heatsink mass TIM adhesion Package Integrated Heat Spreader (IHS) area Package pin geometry Socket retention force Heatsink Inertial Load Current solution approach: Compressive preload Stiff retention clip Socket Package pull-out in vertical shock 13
Design Effectiveness Processor Package Pull-Out - 2 How much preload is required? Linear spring-mass model used for 1st order assessment Assume zero socket retention force Heatsink inertial load FHS = (Heatsink Mass)*(Acceleration input)*(dynamic amplification) kclip Mheatsink Clip stiffness Acceleration under shock Required preload Preq = FHS kMB kMB Local MB stiffness kclip + kMB Required Preload is a Function of Clip and Board Stiffness 14
Design Effectiveness Processor Package Pull-Out - 3 Increase in clip stiffness Allows reduction in required preload Reference design leverages this relationship to minimize required preload: Clip stiffness = 1100 lb/in Required preload ~ 55 lb minimum ~ 70 lb nominal Required preload (lb) 100 90 80 70 Preq = FHS kMB kclip + kMB 60 50 40 30 20 10 Assumptions: MB local stiffness ~ 1300 lb/in HS load, FHS ~ 100 lbf 0 0 200 400 600 800 1000 1200 1400 TotalStiffness clipstiffness
Design Effectiveness Solder Joint Considerations - 1 Solder ball damage Caused by MB flexure under mechanical shock loads Heatsink inertial load reacted through MB bending Heatsink inertial load reacted through MB bending Solder joint subjected to tensile and shear strains CPU heatsink Board curvature sets up critical solder ball strains Severe board flexure under socket and MCH 16
Design Effectiveness Solder Joint Considerations - 2 Current Reference Solution Strategy Limit local board curvature in critical areas through two-point strategy: 1. 2.
Design Effectiveness Solder Joint Considerations - 3 Local Board Stiffening RM and clip create stiff load path between board and package Limits amount of local board flexure during +z shock condition Shock load RM /Clip Reaction at MB mounts Top-side stiffening limits MB flexure 18
Design Effectiveness Solder Joint Considerations - 4 Compressive Preload Places MB into concave curvature in local region surrounding socket and MCH Outer row solder balls placed in compression Delays onset of critical tensile load during shock RM /Clip Note: Pre-stresses critical solder balls with compression Applying a compressive preload on the processor package and on the MCH creates a bow to the board as described reference [6], slide 25.
Design Effectiveness Intel® Pentium® 4 Processor in the 478-Pin Package Clip Design Clip design tailored to achieve target stiffness: Mechanical advantage levers generate preload: 1100 lb/in Mechanical advantage levers used to produce 75 lb preload 60 lb minimum 75 lb nominal Performance under shock load (+z): Compressive load between heatsink and package maintained: no package pull-out Solder ball load prevents from excessive tensile loads, and provides protection to socket sold
Design Effectiveness Intel® 845 MCH Clip Design Clip design tailored to achieve target stiffness of 300 lb/in Mechanical advantage levers used to generate 36 lb preload Performance under shock load (+z): Local board flexure is reduced Solder ball load prevents from excessive tensile loads, and provides protection to MCH solder joint.
Design Effectiveness Thermal Performance Test data indicates 60+ lb preload necessary to optimize TIM performance (Chomerics* T454 - phase change) Reference design preload target: 60 lb minimum 75 lb nominal TIM Resistance (C/W) TIM Thermal Resistance Chomerics* T454 Trendline 0 30 60 Preload (lb) 90 120 *Other names and brands may be claimed as the property of others.
Design Effectiveness Summary Processor Package Pull-Out Socket Solder Joint Protection Use preload coupled with stiff clip to avoid excessive tensile loads on solder joint Thermal Requirements Use preload coupled with stiff clip to avoid excessive tensile loads on solder joint MCH Solder Joint Protection Use preload coupled with stiff clip to prevent pull-out Use preload to achieve TIM performance Chassis-Independent Solution Allows motherboard design flexibility Supports
In Summary Five primary challenges addressed: During shock and vibration events: Avoid processor package pull-out Protect against socket solder joint damage Protect against MCH solder joint damage Prevent TIM thermal performance degradation Allow chassis-independent solution Preload is critical element in addressing each challenge Stiff clip is critical in preventing package pull-out and protecting solder joint Intel Reference Design combines both strategies to meet all critica
Collateral Vendor information for the Intel Thermal Mechanical Enabling Reference design is available at the following web site: http://developer.intel.com/design/Pentium4/components/478pin.htm The following collateral is available in the Pentium® 4 Processor section of the developer.intel.com web site (http://developer.intel.com/design/pentium4/): 1. 2. 3. 4. 5. 6. The following collateral is available in the Chipset section of the developer.intel.com web site (http://developer.intel.
