RoHS Compliant ClearONE™  printed circuit assembly Guidelines Introduction

The standard ClearONE terminator is the industry leader in performance and reliability. The need to  provide a lead free solution for resistor terminator networks in compliance with the RoHS initiative has  required CTS to add a new material set to the ClearONE product line.

Many manufacturers have chosen to utilize Tin/Silver/Copper (Sn/Ag/Cu or SAC) spheres in their BGA  products as a means of eliminating lead. The SAC spheres collapse into the interface solder during the  reflow process, providing an unwanted and less than desirable variation in performance.

This new RoHS ClearONE material set takes advantage of the existing designs while eliminating leadbearing solders. ClearONE solder spheres (10/90 Tin/Lead) and the eutectIC interface solder (63/37  Tin/Lead) are replaced with Tin/Nickel-plated copper spheres and high temperature Tin/Silver/Copper  (Sn/3.5Ag/0.5Cu) interface solder for the RoHS ClearONE terminators. As with the 10/90 spheres, the  copper spheres do not collapse during solder reflow. By utilizing spheres that do not collapse, the RoHS  ClearONE terminators maintain a predictable, consistent standoff height, and the performance  established in the previous non-RoHS product.

The standard ClearONE Ball Grid Array (BGA) terminator material set is described in Figure 1. The  ClearONE product designs provide identical performance in each channel through the use of symmetrical  element layouts and by maintaining predictable standoff spacing.

Figure 1. ClearONE terminator with lead bearing material set

The RoHS Compliant ClearONE terminators continue to take advantage of the symmetrical layout  designs and predictable standoff spacing by utilizing copper spheres that maintain their shape, as shown  in Figure 2.

Figure 2. ClearONE Terminator with RoHS compliant material set

Description

PCB Land Pad Design

The shape of the CBGA land pads on the PCB should be round. The diameters of the PCB  land pads are recommended to be equal to the nominal CBGA solder ball diameter as  provided on the product data sheets, see Figure 3. Tolerance for the CBGA land pad  diameter is + 0.001 inches (+0.025mm). The absolute minimum land pad diameter shall be  0.020" and 0.025" for 1.0mm and 1.27mm pitch parts respectively.

Figure 3. CBGA Solder Ball and PCB Land Pads are equal size

The solder mask surrounding the land pad should not overlap the land pad to ensure maximum thermal cycling reliability, see Figure 3.

The electrical trace leading into the CBGA land pads requires a minimum width trace per the PCB board manufacturing technology used.

CBGA land pads are not to be located on top of any vias.

Vias connected to the CBGA land pads, should have a minimum width connecting trace, with a minimum length of 0.010 inches (0.254 mm), see Figure.

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