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Pad and Fixture Design for Reliable Solder Ball Bond Process Disclosure Number: IPCOM000036116D
Publication Date: 2005-Jan-28
Document File: 4 page(s) / 829K

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The present invention provides for reliable contact between a read/write recording head for a Hard Disk Drive (HDD) and its electrical leads.

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Pad and Fixture Design for Reliable Solder Ball Bond Process

   The solder ball bond process for establishing electrical contact between the pads of a recording head's electrical leads in an HDD may be prone to the creation of defects. This can be due to a temperature gradient during the soldering and cooling process, in which one of the contact pads may cool faster than the other. This can result in the solder on that pad solidifying first, and then the solder on the other contact may condense and solidify later. The result of this process is the creation of a boundary between the 2 regions which is highly stressed, and may lead to cracks or other failure, which degrades or completely breaks the electrical contact between the pads.

   An example illustrating this is shown in the figures below. A solder ball initially placed in contact with the pads is first partially melted, lightly bonding it with the pads ( Figure 1). In this figure, the pads on the recording head are shown in vertical position, and the pads for the electrical leads are shown as horizontal, with the electrical contact leads going away from the pads, to the side of the photo. After a second laser heating pulse, the solder ball is completely melted and flows to form a filet, covering both pads ( Figure 2). It should be noted in Figure 2 however, a circular line runs along the surface of the solder separating the 2 regions of the solder which have crystallized at different times. The larger cross section of the electrical l leads coming away from the lower pad draws more heat from the lower pad, causing the solder on the lower pad to solidify first. The resulting potential impact of this region within the hardened solder is shown in figures 3,4,and 5. The weakened bond is subject to cracking and breaking, under the action of little or no external mechanical stress. In an HDD, the degradation or loss of electrical contact to the read/write recording head would result in poorer error rate or potentially complete loss of functionality. This may render the HDD useless, potentially leading to data loss, and may require the HDD to be replaced.

The present invention solves this problem by a design of the pads and fixture which will put them in good thermal contact, so that the solder on both pads will solidify at the same time. This will eliminate the possibility of a defect region in the solder, thereby assuring the solder contacts' reliability.

We disclose here a design for the contact pads and fixturing for a solder ball bond process in which the pads are placed in direct physical...