A Practical Guide to Understanding and Doing Away with this Common Defect

A Practical Guide to Understanding and Doing Away with this Common Defect

A well-known and often-seen defect, mid-chip solder balling has been plaguing electronics manufacturers for decades. Though some would argue that mid-chip solder balls can, in some cases, be more a defect of aesthetics rather than reliability, their elimination is nevertheless desirable. The mid-chip solder ball occurs when solder is squeezed under the component and away from the pad and is unable to coalesce back during reflow, remaining hidden under the component or appearing out to the side of the device. Several causes for mid-chip solder balling have been suggested and include excess solder paste on the pad, poor hot slump and insufficient wetting. The mid-chip solder ball phenomenon tends to occur more frequently with chip resistors due to the fact that they have tinning on three sides and a reduced solderable surface as compared to capacitors, though capacitors may also be subject to this defect. The reported occurrences of mid-chip solder balls have changed as the industry has moved toward more miniaturized components and lead-free solder paste materials.

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