Page 22 - ChipScale_May-June_2020-digital

Testing AiP modules in high-volume production for

5G applications

By Jose Moreira [Advantest]
T he arrival of 5G promises signals to the AiP antenna array with the For high-volume production testing,

enhanced mobile broadband
(eMBB), massive machine- needed gain and phase to each radiating the objective is to check functionality
of the DUT and not its compliance to
element. The module would then usually
type communication (mMTC), and ultra- only require power, digital control the standard. Low cost of test is critical
reliable low-latency communication signals, and modulated intermediate because most of the end applications
(URLLC). eMBB is already available frequency (IF) signals. are consumer-oriented. Also, to keep
to consumers, who can pu rchase AiP modules for 5G handsets need to costs down it is important to be able to
5G-capable handsets that can operate be extremely small to fit into the modern reuse as much as possible the test cell
on 5G networks deployed by carriers in cellphone form factor, and a multiple of infrastructure already used for testing
many regions throughout the world. But them need to be used in a single cellphone RF integrated circuits.
as 5G rolls out, the test community faces because the user’s hand position has a From a test engineering point of view
challenges and opportunities. That’s significant impact on the transmitted there are multiple possible steps in
particularly true regarding the antenna beam loss. Also, the AiP modules in a testing an AiP module. First, the RF chip
arrays that will connect handsets to base cellphone might not be all equal, but in (e.g., a wafer-level chip-scale package
stations. fact have different antenna configurations [WLCSP] part), is tested at wafer level.
Most initial 5G deployments will depending on the handset design. This test can be either very simple and
take place only using the sub-6GHz The 3GPP standard defines three low cost (e.g., mainly DC or even a
frequencies used for previous generations methods for the over-the-air (OTA) wire loopback on the mmWave ports),
of cellular technology, but they will be standard compliance testing of AiP or it can also include full mmWave
enhanced later with the possibility of modules: direct far field, indirect far parametric measurements using an
short-range high data rate connections field (e.g., compact antenna test range, appropriate probe card and automatic test
using mmWave frequencies. 5G new or CATR), and near-field to far-field equipment (ATE) system. After the AiP
radio (5G NR) defines two ranges, transformation. Each of these methods module is assembled, the same question
frequency range 1 (FR1) and frequency have advantages and disadvantages, on the types of tests to be performed
range 2 (FR2). FR1 includes the sub- but they all require relatively large test on the AiP module can be evaluated. It
6GHz frequencies, but FR2 opens up chambers and a complex manipulator to might consist of a simple low-cost DC
mmWave frequencies above 24GHz for rotate the AiP device under test (DUT) or test or even some kind OTA loopback
5G deployment. 5G NR leverages the FR2 the measurement antenna. test, to a full parametric OTA test with
frequencies to achieve larger modulation a measurement antenna. Finally, after
bandwidths (for example, 800MHz). But integration in the end product (e.g.,
because of the high transmission loss at a 5G handset) a system-level type of
these frequencies, it is necessary to use test might also be performed. The test
antenna arrays for multiple-input and strategy at each stage depends on the
multiple-output (MIMO) functionality overall test strategy for the AiP module.
and to focus the transmission beam (beam Another important point is the AiP
forming) in both the base station and the module calibration. For proper beam
consumer’s handset. These arrays come steering of the AiP module, it is critical
in the form of antenna-in-package (AiP) that one is able to accurately set the
modules, which are a critical part of the gain and phase at each antenna element.
current 5G wireless communication wave. If this accuracy cannot be guaranteed
For the handset, these AiP modules by design or a built-in self-test (BIST)
will usually have an array of dual calibr at ion tech n ique, t hen t h is
polarized patch antennas for top firing calibration step needs to be performed at
and, in some instances, also an array of one of the test stages of the AiP module
dipole antennas for side firing as shown testing, or worst case at system level
in Figure 1. To keep RF losses to the when the handset is assembled.
antenna radiators to a minimum, the AiP We will now concentrate on the case
module includes an RF integrated circuit that a parametric OTA test is required
that provides the modulated mmWave Figure 1: Drawing of an example of a generic antenna for an AiP module, but because of
array module, comprising 12 dual-polarized patch
antenna elements and seven dipole antenna elements.
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