Lead-Free BGA TerminationsLead-Free BGA Terminationswith Tin/Lead Pastewith Tin/Lead Paste

Bob WillisBob Willis

The Story So Far!!!!The Story So Far!!!!This is a simple trial to show what happens when BGAs are reflowed with tin/lead paste, when the balls are lead-free. If you maintain existing profiles BGAs with tin/silver/copper or tin/silver may not reflow. Depends how high your tin/lead profile is ???

If the coplanarity is fine and there is no difference on delta T over the complete BGA then fine. If there is a difference across the BGA, which there normally is open joints can occur as some balls reflow others don’t but the paste obviously does.

If the BGA’s PCB warp which some do and the balls do not go into a liquid phase but the paste does opens can still occur.

Many thanks to Rob Horsley for the BGAs and mini stencil for the trial, no BGAs Many thanks to Rob Horsley for the BGAs and mini stencil for the trial, no BGAs

were harmed in the making of this feature film!!!!were harmed in the making of this feature film!!!!

Lead-Free BGA with Tin/Lead PasteLead-Free BGA with Tin/Lead Paste

uBGA 196 Sn-3.5Ag balls (221oC)Tin/Lead Paste 62/2/37 (179oC)Stencil thickness 0.005”Nickel/gold pad surfacesReflowed on 5 zone oven with tin/lead profile in air

Also videos reflowing on hot plate with tin/lead profile to compare the process result and the simulation

Lead-Free BGA with Tin/Lead Paste VideosLead-Free BGA with Tin/Lead Paste Videos

BGA Reflowing, balls did not reflow invideo simulation or during reflow. Profile was designed to do this!! (video01)

BGA compressed during simulatedreflow just to show non ball reflow on samples reflowed on hot plate (video02)

Lead-Free BGA with Tin/Lead PasteLead-Free BGA with Tin/Lead Paste

Balls have not reflowed paste has this is not as clear on these images, must try harder. Both reflow and simulation provided the same views.

Lead-Free BGA with Tin/Lead PasteLead-Free BGA with Tin/Lead PasteBalls have not reflowed paste has wettedpads this is shown by the perfect ball circle of the x-ray image after reflow

The second x-ray does show the wetting of the paste to the ball and the pad after reflow

Lead-Free BGA with Tin/Lead PasteLead-Free BGA with Tin/Lead PasteBalls have not reflowed as planned but tin/lead paste has reflowed and wetted the joint interfaces

This was the same in the simulation providingthe same type of image in the sections. Sample sections are from reflow.