In the assembly of

integrated circuit An integrated circuit (IC), also known as a microchip or simply chip, is a set of electronic circuits, consisting of various electronic components (such as transistors, resistors, and capacitors) and their interconnections. These components a ...

packages to

printed circuit board A printed circuit board (PCB), also called printed wiring board (PWB), is a Lamination, laminated sandwich structure of electrical conduction, conductive and Insulator (electricity), insulating layers, each with a pattern of traces, planes ...

s, a head-in-pillow defect (HIP or HNP), also called ball-and-socket,https://aimsolder.com/sites/default/files/head-in-pillow_bga_defects.pdf is a failure of the

soldering Soldering (; ) is a process of joining two metal surfaces together using a filler metal called solder. The soldering process involves heating the surfaces to be joined and melting the solder, which is then allowed to cool and solidify, creatin ...

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 pu ...

(BGA) package, the pre-deposited

solder ball In integrated circuit packaging, a solder ball, also a solder bump (often 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 ...

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, which requires a higher processing temperature. The defect can be attributed to a chain of events during soldering. Initially, the ball is in contact with solder paste. During heating, the board and components undergo thermal expansion, can flex, and some of the balls can be lifted off the paste. Oxidation occurs rapidly at elevated temperature, and when the surfaces come in contact again, the residual flux activity may not be sufficient to disrupt the oxide layer. The solder paste composition, eg. flux with higher activation temperature, together with the wetting characteristics of the solder ball, are the most significant mitigation factors. 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. Intermit ...

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 Transmission line, electrical lines by observing Signal reflection, reflected Pulse (signal processing), pulses. It can be used to characterize ...

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

References

Further reading