Page 52 - Chip Scale Review_November December_2021-digital

because of its long signal length and its high manufacturing should be matched. For this, the signal diameter of the coaxial
cost [3]. To address these disadvantage, a coaxial elastomer spring socket should be smaller than the ball pitch. For this
socket based on the elastomer socket is proposed. Such a coaxial reason, when the diameter of the signal becomes very small,
elastomer socket solves the crosstalk problem, and has the the manufacturing cost of the coaxial spring socket increases as
advantages of a shorter length, lower transmission loss, and a the mechanical components, such as the spring and barrel that
lower manufacturing cost than the spring socket. make up the spring socket, must be made smaller. Therefore, the
demand for a high-frequency test socket with a short conductive
Crosstalk in an elastomer socket and a spring socket path and low manufacturing cost is growing.
When the test socket is used at high frequency, an
electromagnetic wave is generated from the signal—this wave Elastomer socket with metal housing to prevent
affects the adjacent signal line through the insulating part. This crosstalk
effect is called crosstalk, and the smaller the interval between In this article, we propose the use of a coaxial elastomer
signals and the higher the frequency, the greater the crosstalk socket with a metal frame instead of the typical elastomer socket
effect. In the same position as the package ball, the test socket configuration that uses a silicone rubber for the insulating part.
has a conductive path made of powder with gold plating applied The ground is configured to form a ground connection notch
to nickel material. Crosstalk also occurs in silicone rubber inside the housing hole so that the conductive path and the metal
(Figure 1a), which is an insulator in the elastomer socket. housing are short circuited, so that the reference to which the
Crosstalk occurs in an insulator housing made of ULTEM™ and return path of the signal is realized becomes the metal housing.
PEEK material comprising the spring socket (Figure 1b). It has Figure 3 shows the structure of the coaxial elastomer socket.
a conductive path composed of BeCu or Pd alloy material with a
gold-plated barrel and a spring that acts as an elastic body.

Spring socket with metal housing to prevent crosstalk
In the case of the spring socket, a coaxial spring socket with
an insulating housing applied to a metal housing is proposed as
a way to prevent crosstalk. The coaxial spring socket with an
insulating housing applied to a metal housing prevents signal
interference of the electromagnetic wave generated from the
signal to the adjacent signal as the metal housing acts as an
electromagnetic shielding. If, however, the housing is made of
metal but does not have an insulating housing, a short circuit
occurs. As shown in Figure 2, when the outside of the signal is
composed of an insulator, a short circuit is prevented.

Figure 3: Structure of a coaxial elastomer socket.
The coaxial elastomer socket also needs to implement a small
Figure 2: Structure of a coaxial spring socket. signal diameter for impedance matching, but there is no significant
increase in manufacturing cost to do so. This is because of the
Through the structure shown in Figure 2, the coaxial spring implementation of powder gathering by magnetic force rather
socket has the advantage of improving the signal transmission than because of the miniaturization of various parts made by
characteristics by shielding the electromagnetic wave of the machining compared to a spring socket. Because the length of
signal at high frequency, but it has the disadvantage that the the conductive path in a coaxial elastomer socket is much shorter
signal length is long. If the signal length is long, the inductance than that of the spring socket, the inductance value is low and
value increases, and that leads to a degradation of signal the signal transmission characteristics are excellent. Moreover, it
transmission characteristics. In order to optimize the reflection has a crosstalk shielding effect because it is completely wrapped
characteristics of the signal, the characteristic impedance around the signal with a metal frame. It has the same shielding

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