This is from a section of an ALtera EP2SGX130-5 STRATIX 2 leadfree 1,508 ball BGA. What can be causing this? It is from an unused board (not assembled in a unit, or in the field, but it did pass electrical and function test. There are three of them in the section we did. The lab is calling this pad cratering. The BGA was soldered in a 7 zone Vitronics Soltec oven and when thermocoupled we saw: Peak Temp: 245�C, Max Slope: 2.89, Time above liquidus: 62 seconds. We use SAC305 Indium paste. Any help would be appreciated.
Was this a lead-free capable material that fits into IPC 4101/126 or /129, like an Isola 370HR? I would not be surprised because from the picture I think I can see resin underneath the lifted copper, which is an interlaminate separate.
This is a well known occurence with phenolic lead-free materials, typically those with fillers like the 370HR has. My customers have successfully avoided this by switching to lead-free capable materials that fall into the IPC 4101/99 or /124 categories. Even though these materials are less robust from a purely thermal standpoint, they perform much better in terms of decreased moisture absorption and increased interlaminate adhesion strength.
IPC T-50, Revision H, Terms and Definitions for Interconnecting and Packaging Electronic Circuits, 96.2176 Pad Cratering. A separation of the pad from the printed board resin/weave composite or within the composite immediately adjacent to the pad as a result of mechanical and/or thermal stress.
Generally: * Lead-free solder connections are stiffer than tin-lead connections * Some lead-free laminate materials are more brittle than conventional tin-lead materials.
This reduced flexibility, combined with: * Higher soldering tempera�tures required for lead-free assembly * Greater flexing of BGA during these higher temperature swings caused by Cte mismatch between the BGA interposer and the the board ... could transfer more strain to the laminate, causing a pad seperation failure of the BGA, especially at corner pads.