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9 SMT Board Assembly Process
Recommendations
9 SMT Board Assembly Process Recommendations .......................................................................9-1
9.1 Introduction............................................................................................................................9-2
9.2 Solder Paste Printing..............................................................................................................9-2
9.3 Component Placement ...........................................................................................................9-2
9.4 Reflow Soldering ...................................................................................................................9-3
9.4.1 Pb-free vs SnPb Reflow Soldering ................................................................................9-3
9.4.2 Reflow Profile Development Considerations ................................................................9-3
9.4.2.1 Reflow Profile Board Preparation .............................................................................9-4
9.4.2.2 Minimum Solder Joint Peak Temperature.................................................................9-5
9.4.2.3 Maximum Solder Joint Peak Temperature ................................................................9-5
9.4.2.4 Time Above (Initial) Melting Point...........................................................................9-5
9.4.2.5 Rising and Falling Ramp Rate...................................................................................9-6
9.4.2.6 Reflow Equipment .....................................................................................................9-6
9.4.2.7 Reflow Atmosphere ...................................................................................................9-6
9.4.2.8 Board Warpage ..........................................................................................................9-7
9.4.2.9 Double Sided SMT Board Assembly ........................................................................9-7
9.4.3 Sample Reflow Parameters............................................................................................9-7
9.4.4 Sample Reflow Profiles .................................................................................................9-8
9.4.4.1 Sample Desktop Reflow Profile ................................................................................9-9
9.4.4.2 Sample Mobile Reflow Profile ..................................................................................9-9
9.4.4.3 Sample Server Reflow Profile .................................................................................9-10
9.5 Rework.................................................................................................................................9-10
9.5.1 Pb-free vs SnPb Rework..............................................................................................9-10
9.5.2 Risk of SnPb and Pb-free Mixing................................................................................9-10
9.5.3 Rework Profile Board Preparation...............................................................................9-10
9.5.4 Pad Cleanup After Component Removal ....................................................................9-11
9.5.5 Paste Printing Methods at Rework ..............................................................................9-12
9.5.6 Re-balling BGAs Not Recommended .........................................................................9-13
9.5.7 Sample Rework Parameters.........................................................................................9-14
9.5.8 Rework Profile Development ......................................................................................9-15
9.5.9 Sample Rework Profiles ..............................................................................................9-16
9.5.9.1 Sample BGA Rework Profile ..................................................................................9-16
9.5.9.2 Sample Socket Rework Profile................................................................................9-17
Intel Packaging Databook 9-1 Board Reflow Process Recommendations
Revised 12-2007
9.1 Introduction
This chapter addresses the surface mount technology (SMT) board assembly process for reflow
soldering SMT components to boards, as well as rework soldering for removing and replacing
individual components on already-assembled boards.
The information in this document is for reference only. Manufacturing processes are unique, and may
require unique solutions to ensure acceptable levels of quality, reliability, and manufacturing yield.
Due to differences in equipment and materials, customer-specific process parameter development and
validation is required.
9.2 Solder Paste Printing
Standard tin-lead (SnPb) solder paste alloy is composed of 63% tin (by weight) and 37% lead, which is
commonly expressed as 63Sn/37Pb or Sn/37Pb, a eutectic composition that melts at 183C.
Although there are a number of lead free (Pb-free) alloys, the most commonly used compositions
contain tin, silver, and copper, commonly expressed as SAC, for SnAgCu. Within SAC solders, by far
the most common usage is Sn/3Ag/0.5Cu, a near-eutectic which melts between 217