Ball Impact Responses of Ni- or Ge-Doped Sn-Ag-Cu Solder Joints

Abstract

In this work, we present ball impact test (BIT) responses and fractographies obtained at an impact velocity of 500 mm/s on Sn-4Ag-0.5Cu, Sn-1Ag-0.5Cu, Sn-1Ag-0.5Cu-0.05Ni, Sn-1.2Ag-0.5Cu-0.05Ni, and Sn-1Ag-0.5Cu-0.05Ge package-level solder joints. The solder joints are bonded on substrate pads of either immersion tin (IT) or direct solder on pad (DSOP) surface finishes. Differences of BIT results with respect to multi-reflow are also reported. Taking the impact energy as an indication of board-level drop reliability of the solder joints, the BIT results indicate that better reliability can be achieved by adopting Sn-Ag-Cu solder alloys with low Ag weight contents as well as IT substrate pad finish rather than DSOP. Moreover, the addition of Ni or Ge to the solder alloy provides a large improvement; Ni alters the interfacial intermetallic compound (IMC) structure while Ge enhances the mechanical behavior of the bulk solder.

Interfacial reactions and mechanical properties between Sn–4.0Ag–0.5Cu and Sn–4.0Ag–0.5Cu–0.05Ni–0.01Ge lead-free solders with the Au/Ni/Cu substrate

“…The k value is increased as the aging temperature is increased in the SACNG/substrate couples. These results are similar to that in the SAC/substrate couples and literature data [25,26]. The IMC evolution in both couples is listed in Table 3.…”

“…Massive research groups have studied interfacial reactions between Sn-Ag and Sn-Ag-Cu alloys with Ni or Cu or Au/Ni/Cu substrates [5,[11][12][13][14][15][16][17][18][19][20][21][22], and several literatures had regarded with interfacial reactions and the mechanical properties of Sn-Ag-Cu alloys by adding a minor amount of Ni or Ge elements to the Au/Ni/Cu substrate [8,21,[24][25][26][27][28][29][30][31]. The Sn-4.0Ag0.5-Cu alloy is one of popular lead-free solders and the Au/Ni/Cu multi-layer is the common UBM structure in electronic packaging.…”

Nanotribological Characteristics of Cu6Sn5, Cu3Sn, and Ni3Sn4 Intermetallic Compounds

“…[2][3][4][5][6] Binary IMCs, such as Cu 6 Sn 5 , Cu 3 Sn, and Ni 3 Sn 4 , and ternary or multi-element IMCs, such as (Cu 1Àx ,Ni x ) 6 Sn 5 and (Ni 1Ày ,Cu y ) 3 Sn 4 , are typical species present on the interface between the Sn-based solder and the Cu or Au/Ni/Cu pad metallization. 7,8 Because of the irregular shapes and micrometer scales of these IMCs in a solder joint, their mechanical properties are difficult to obtain by conventional test methods for bulk materials.…”

Impact Behavior of Thermomechanically Fatigued Sn-Based Solder Joints

“…The rapid increase in the number of miniaturized consumer electronics which can be easily dropped by the user has resulted in significant interest in the impact response of such interconnects. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] Impact reliability tests carried out by dropping the device, either once or a specific number of times, from a chosen height provide a simple means of quantitative joint system evaluation. 16 However, such studies do not provide sufficient information to select solder materials and/or joint geometries for improving the impact reliability of solder interconnects.…”

“…These studies impose impact loading on the bonded solder balls, providing results from a better controlled impact loading scenario. [5][6][7][8][9] However, it is still difficult to realize the true nature of impact loading experienced by solder joints present in electronic interconnects from these studies. Solder interconnects are part of a multicomponent system, and the loading realized by the solder region is a consequence of the impact imposed at some other location in the system.…”