South Central

Since the 1980s, manufacturers have used barcodes to tag PCBs at the start of their way
around the production cycle. Traceability is becoming more important as flexible
manufacturing gains popularity; different versions or models of an electronic product can be
produced based on the same PCB with different combinations of components mounted on it,
depending on the demand for the various models. The product a PCB is intended for could
even be changed half way around the cycle. Traceability is also very important in safetyrelated
applications such as the aerospace sector, because if certain components malfunction
and the parts have to be traced, data on the PCB’s history is required in as much detail as
possible, as quickly as possible. Tracking goods around the manufacturing process therefore
needs to be done in an automated, machine readable way.
Barcodes are simple and inexpensive to implement although they have limited features. The
barcode pattern is printed onto a paper label which is glued onto the PCB, taking up a
relatively large amount of space on the board (not good for modern PCBs, where board
space is critical since the boards are as densely populated as possible). The barcode is read
by a scanner which needs to be able to “see” the paper label to read it, meaning it cannot be
read from outside an enclosure. The PCB has to be in the right orientation with the barcode
visible to the scanner. If the barcode gets torn, burnt, stained or greasy, it may render it
unreadable.
Low information density
The data a barcode holds is simply a number which identifies the PCB. Data about that PCB
can has to then be retrieved from a database. 2D barcodes have been introduced in recent
years which are more reliably read by barcode scanners, even after being soiled or torn. They
have a higher information density than their 1D cousins and can be read faster and more
reliably. However the scanning technology for these barcodes requires high resolution
camera equipment and the cost may outweigh the benefits.
RFID (radio frequency identification) devices have been proposed as a solution to tracking
PCBs around the manufacturing process. An RFID chip, mounted on the board and combined
with an antenna, provides a durable way of attaching a large amount of data about the PCB
to each board. RFIDs can be read from a scanner at larger distances than barcodes, and do
not require line of sight; the RFID chip can be read regardless of whether it is on the
underside or opposite side of the PCB and can even be read from outside an enclosure.
Increased readability is of paramount importance.
Another feature of RFIDs is that they can be programmed and reprogrammed to store
additional information about each individual PCB, such as:
? Manufacturer data
? Part number or order number
? Production date
? Configuration status
? Software version
This information can be updated part way around the cycle if any of these parameters
changes. There should be an ample amount of storage on an RFID chip for the traceability
data required.
Challenges for RFIDs
Implementing RFID technology is not without challenges. A major roadblock in adoption to
date has been that mounting an RFID chip requires specialised knowledge of RF design, for
such key elements as design of the antenna and the associated filters and impedance
matching circuit.
The antenna matching circuitry is necessary to achieve the required sensitivity, and can be
complex to design, especially considering the limited PCB board space. The size of the RFID
chip itself also contributes to the board space required, and it has to be placed and soldered
precisely onto the antenna pattern on the board. A wide band pass UHF filter is required if the
RFID is to respond to the different frequencies used worldwide, and this would be very
difficult to achieve without the matching circuit.
Technology that overcomes some or all of these challenges has been developed by leading
ceramic components manufacturer Murata.
MAGICSTRAP® ceramic module
Murata has used its LTCC (low temperature co-fired ceramic) technology to create an RFID
device which combines the latest in ceramic materials with innovative design to produce a
tiny module, called MAGICSTRAP® (see figure 1). The MAGICSTRAP® RFID module
requires little RF expertise and no soldering or conductive glue to mount. Murata has
developed and patented inductive-coupled terminals especially for the MAGICSTRAP®
module, which do not require direct connection to the antenna – proximity is enough. It can
simply be mounted onto the antenna using ordinary adhesive or even sticky tape. In terms of
placement, sticking the chip on the antenna pattern to the nearest millimetre is sufficient –
traditional package types for RFID modules require micron accuracy, so this is a huge step
forward.

The module comprises Murata’s LTCC (low temperature co-fired ceramic) substrate, plus IC
and packaging. All the necessary RF circuitry is embedded within the LTCC substrate of the
module, with the IC then mounted on top (see figure 2). The LTCC substrate incorporates the
wideband antenna filter circuit, the antenna impedance matching circuit and 10kV ESD
protection. It is only 550um thick

The antenna itself utilises a metal pattern and the ground plane of the PCB as part of a dipole
antenna (see figure 3). The ground plane of the PCB receives the RF wave from the air while
the antenna pattern fixes the centre frequency and bandwidth of the RFID. It is important to
note that a change in PCB supplier may result in even the slightest change to the properties
of the PCB ground plane material, and affect the accuracy of the circuit.

The embedded wideband antenna filter circuit, plus a single wideband antenna (for which
Murata provides a reference design), allow MAGICSTRAP® to be readable over the band
860-960 MHz at a range of up to 5m. This means the same module and antenna pattern can
be used worldwide (in Europe, the US and Japan), saving cost and inventory for
manufacturers. It is possible to use different size/shape antenna patterns which trade off
surface area versus read distance (see figure 4). Since the RFID recognizes the ground
plane of the PCB as part of the dipole antenna, it’s also dependent on the size of the PCB.
The largest antenna shown here is 32 by 13mm and gives a read range of 5m, but bigger
antennas are possible on larger PCBs for applications such as white goods.

Several options for memory capacity are available by selecting a different RFIC without
changing the antenna design. MAGICSTRAP® modules with memory between 512bit and
2kbit are available.
In summary, RFID technology allows tracking data to be attached to a PCB in an easy and
machine readable way. Some of the challenges associated with use of RFIDs include design
of an associated RF circuit, mounting the RFIC or module accurately and making sure the
band pass filter is wide enough to accept frequencies used for RFID chips worldwide.
Murata’s MAGICSTRAP® is a tiny RFID module that incorporates all the necessary RF
circuitry, embedding it within the multilayer ceramic substrate to remove the need for RF
expertise. It can be mounted with only millimeter accuracy using ordinary adhesive or sticky
tape, with the ease of handling of an SMD component. Murata’s strengths in multi-layer
ceramic devices are the enabling technology for this product, which will ultimately drive
widespread adoption of RFID technology.