Pb-Free option of SRAMs

Question:

What are the differences in reflow/assembly process required by Pb-Free devices?

 

Answer:

There are requirements and conditions for the Pb-Free devices reflow process and are tabulated in the Cypress Pb-Free reflow profile shown below. The product must meet two stringent requirements, zero lead and high temperature (260 ?C) reflow capability. Higher temperature reflow capability is needed because Pb-Free solder pastes melt at higher temperatures. The Pb-Free devices are marked with an 'X' on the package in the standard parts number.

For leadframe-based packages, Nickel Palladium Gold (Ni-Pd-Au) and Matte Tin (Sn) are the primary options. Nickel Palladium Gold (Ni-Pd-Au) for internally manufactured product and Tin (Sn) for subcontract manufactured products.

BGA packages will use Tin-Silver-Copper (SnAgCu) instead of Tin-Lead (SnPb) balls 

Cypress Semiconductor 260 Pb-Free Reflow Profile 

                                                                                                                    
   

PROFILE ELEMENTS

  
   

IR - INFRA RED REFLOW

  
   

Ramp Rate 217 ?C

  
   

3 ?C /sec max 

  
   

Preheat Temperature 150 ?C (+/-25?C)

    

 

  
   

60 to 120 seconds max 

  
   

Time 50 ?C to Peak Temperature 

  
   

3.5 minutes, 6 seconds max 

  
   

Temperature maintained above 217 ?C 

  
   

60 to 150 seconds 

  
   

Time within 5 ?C of actual peak

    

temperature 

  
   

10 to 20 seconds 

  
   

Peak temp range

  
   

260 ?C (-5/+0) ?C 

  
   

Ramp-down rate 

  
   

6 ?C /second max