In the assembly of

integrated circuit An integrated circuit or monolithic integrated circuit (also referred to as an IC, a chip, or a microchip) is a set of electronic circuits on one small flat piece (or "chip") of semiconductor material, usually silicon. Large numbers of tiny ...

packages to

printed circuit board A printed circuit board (PCB; also printed wiring board or PWB) is a medium used in Electrical engineering, electrical and electronic engineering to connect electronic components to one another in a controlled manner. It takes the form of a L ...

s, a head-in-pillow defect (HIP or HNP) is a failure of the

soldering Soldering (; ) is a process in which two or more items are joined by melting and putting a filler metal (solder) into the joint, the filler metal having a lower melting point than the adjoining metal. Unlike welding, soldering does not involv ...

process. For example, in the case of a

ball grid array A ball grid array (BGA) is a type of surface-mount packaging (a chip carrier) used for integrated circuits. BGA packages are used to permanently mount devices such as microprocessors. A BGA can provide more interconnection pins than can be p ...

(BGA) package, the pre-deposited

solder ball In integrated circuit packaging, a solder ball, also a solder bump (ofter referred to simply as "ball" or "bumps") is a ball of solder that provides the contact between the chip package and the printed circuit board, as well as between stacked pa ...

on the package and the solder paste applied to the circuit board may both melt, but the melted solder does not join. A cross-section through the failed joint shows a distinct boundary between the solder ball on the part and the solder paste on the circuit board, rather like a section through a head resting on a pillow. The defect can be caused by surface oxidation or poor wetting of the solder, or by distortion of the integrated circuit package or circuit board by the heat of the soldering process. This is particularly a concern when using

lead-free solder Solder (; NA: ) is a fusible metal alloy used to create a permanent bond between metal workpieces. Solder is melted in order to wet the parts of the joint, where it adheres to and connects the pieces after cooling. Metals or alloys suitable ...

, which requires higher processing temperature. Since the warping of the circuit board or integrated circuit may disappear when the board cools, an

intermittent fault An intermittent fault, often called simply an "intermittent", (or anecdotally "interfailing") is a malfunction of a device or system that occurs at intervals, usually irregular, in a device or system that functions normally at other times. Intermitt ...

may be created. Diagnosis of head-in-pillow defects may require use of X-rays or EOTPR (

Electro Optical Terahertz Pulse Reflectometry A time-domain reflectometer (TDR) is an electronic instrument used to determine the characteristics of electrical lines by observing reflected waveforms. It can be used to characterize and locate faults in metallic cables (for example, twisted pa ...

), since the solder joints are hidden between the integrated circuit package and the printed circuit board.

See also

References

Further reading