DEK has developed wafer bumping and ball placement solutions for packaging applications by using efficient screen printing techniques and enabling technologies such as enclosed print head material deposition.

“Customers are looking for reduced costs on several levels,” says Richard Heimsch, president. “Manufacturers want lower initial equipment investment, long-term ownership and tooling costs. DEK has responded to these requirements by delivering a flexible platform that can deposit paste and place solder flux and solder balls, while handling devices in different input formats.”

For bumping at the wafer and substrate levels, a simple print and reflow method allows for single stroke, unlimited bump quantity with bump height targets of 80 to150 microns on pitches of 150 to 500 microns. This technique requires strict application of design rules when creating the stencil, which is generally electroformed.  The design of the bond pads must allow sufficient contact area to achieve good solder joint strength for a given stand-off.  The technologies that allow printing platforms to meet these semiconductor packaging requirements include automated wafer handing systems, Vortex clean-room compatible paperless cleaning systems and ProFlow enclosed print head technology which is said to deliver paste volume transfer and uniformity.

When pitch and bump size is appropriate, placing instead of forming solder bumps at the wafer and substrate levels is an alternative. DirEKt Ball Placement places solder balls as small as 0.3 mm in diameter onto substrates or wafers, with fine-pitch accuracy and first-pass yields reportedly better than 99%. Flux is deposited at each interconnect site. Then, the fully enclosed ProFlow ball transfer head guides each solder ball directly to the surface of the stencil and a controlled placement force seats each ball into the flux. Cycle time is fast and completely independent of I/O count.

DEK, www.dek.com

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