For the FPC antenna design guidelines, we mainly talk about the below four points. FPC antenna structure design guidelines FPC antenna material selection FPC antenna assembly process requirements FPC antenna reliability test requirements

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FPC Antenna Design Guidelines
For the FPC antenna design guidelines, we mainly talk about the below four points.
FPC antenna structure design guidelines
FPC antenna material selection
FPC antenna assembly process requirements
FPC antenna reliability test requirements
For handheld, wearable design, smart home, and other small size IoT products, rarely use an
external antenna, generally use the built-in antenna, built-in antenna mainly includes ceramic
antenna, PCB antenna, FPC antenna, spring antenna, etc. The following article is for the
introduction of built-in FPC antenna design guidelines.
FPC antenna advantages: applicable to almost all small electronic products, can do 4G LTE
full-bands such as more than ten bands of complex antenna, good performance, the cost is
relatively low.
FPC antenna disadvantage: need to debug according to each product individually.
FPC antenna structure and tolerance specification
1. FPC antenna design size tolerance
FPC antenna size tolerance is generally ±0.15mm if more than 80 less than 100 according to
±0.20mm.
Antenna tolerance of ± 0.30mm, because the ink diffusion in the printing process will overflow.
The positioning hole center's distance tolerance ± 0.10mm, the minimum slot width of 0.8mm.
Due to material deformation, mold punching deviation, to meet the product performance and
appearance of the premise, the appropriate relaxation of tolerance, one is conducive to
production operations; the second is conducive to improving the product qualification rate,
reducing costs.
2. FPC antenna structure Stress hole/slot design

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FPC antenna in the intersection of the bend lay copper, the width as far as possible to control
within 1.0mm, otherwise must set the stress relief hole/slot or needle cut line to reduce the
internal stress.
3. FPC antenna housing design
If FPC antenna in the outer housing surface, the FPC antenna area need to sink 0.3mm (FPC
thickness 0.15mm) and housing surface made of 22~24# spark pattern, grain surface than glossy
paste effect is good, not easy to warp.
FPC antenna commonly used positioning method is divided into positioning column/hole
positioning or boundary positioning; (positioning column diameter Φ0.8X0.3H; boundary
positioning single side gap 0.05-0.1mm.)
FPC antenna area tries not to make curved surface because the curved surface stick FPC will
wrinkle, long time placing will also warp, thus affecting the antenna performance and beauty.
Solution:
Try to change the curved surface into a slope. If you can only do the curved surface, it must be a
single-direction curved surface.
Such as some FPC antenna is printed double-sided ink leads to local buckling. A curved surface or
bevel can effectively avoid buckling if the shell is designed in a single direction.
Antenna FPC and antenna cover film are often used on the top surface and the surrounding side,
need to bend, bending easily to produce warping problems. The antenna warping problem has
occurred in many models. Three sides are single surfaces. Although the curvature is not large, the
production found warping. After analysis and verification, the antenna can effectively improve
the warping problem by changing the curved surface of the side to a flat surface.
1) The gluing width A of the side plane should be more than 4mm.
2) Side plane bending angle B Side plane bending angle can be from 0-90 degrees. The larger the
angle is, the wider the side plane should be after overbending.
(3) Excessive R angle R0.2-0.4mm can be taken.
(4) FPC in the excessive R angle to hit the process hole (recommended diameter of ≥
0.8-1.2mm) can reduce the bending stress.
4. FPC antenna structure corner design
The FPC antenna laying copper edge is at least 2mm from the PI edge for the shape corner parts.
When the antenna must lay copper to the edge of the FPC antenna, it is necessary to continue
extending the FPC antenna and then bending it to the inside of the structural part.

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5. FPC antenna design structure cracking slot design
It is necessary to set the cracking width> slot (slot width 1mm) to prevent wrinkling and warp in
some large shell arc surfaces.
6. Adhesive sticker in FPC antenna design
The antenna release paper must be cut in sections according to the pasting steps to ensure that
the
The operator will not touch the adhesive backing. It is recommended to place the positioning
pillar on the first step of the paste. It is to facilitate effective positioning. The release paper open
line is usually set in the middle of the two positioning holes to tear off half of the alignment first
and then tear off the other half of the sticker.
The choice of FPC antenna material
1.FPC antenna ink is mainly composed of epoxy resin plus related filler.
Usually with the thermosetting oil after a dummy, silk ink needs to be heated and baked to dry.
Generally, choose light black bright white green; printed resist thickness of 0.015mm-0.02mm.
The most common problem is ink cracking, so wear resistance, adhesion, foldability, ink thickness,
Acid and alkali resistance, ultraviolet light, and other tests.
2. FPC antenna copper foil usually uses electrolytic copper or calendering copper.
The thinner the overall thickness is not easy to warp, the recommended overall thickness of
0.12mm. The material needs to choose PI18/12.5 or PI18/25 (PI half and half is softer, not easy to
warp, preferably PI half and a half), generally do not consider using PET.
3. FPC antenna adhesive is according to the bonding characteristics, such as the need for
high-temperature-resistant.
The 3M adhesive sticker (0.05mm) has an excellent bonding effect, good processability, good
temperature resistance, anti-corrosion, good holding adhesive force;
It has long-term temperature resistance. Short-term temperature resistance also can be.
4. Total thickness of finished FPC antenna:

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ink+substrate+copper foil+backing adhesive total thickness 0.12mm-0.15mm.
5. FPC antenna nickel gold plating.
General use of chemical replacement gold plating and electroplating two kinds of gold plating,
must first nickel plating and then gold plating, which is to prevent gold atoms and copper atoms
penetrating each other, resulting in gold layer instability;
Two processes compared, electroplating process gold thickness can do more than 0.3um or even
thicker;
And chemical plating gold thickness can only be <0.075um; because FPC plating does not have
bending toughness, and the thicker the gold plating cost, the higher the cost. It is recommended
that the gold thickness control: 0.025um-0.075um.
FPC antenna assembly process requirements
1. FPC antenna paste before the structure must ensure that the surface clean, such as apparent
oil, need to be cleaned or ultrasonic cleaning; it requires shell material manufacturers to use
vacuum plasma equipment for surface activation treatment of structural parts.
2. The FPC paste environment requires a high degree of cleanliness in the space.
3. FPC paste requires the operator to operate with finger gloves so as not to leave fingerprints
and sweat after the backing touches the hands and affects the bonding quality.
4. Use glue for local easy to warp parts, or primer, activator treatment.
5. Paste, ask the operator to tear the antenna end from the release paper first, align with the
paste part of the product, tear and paste until the paste is finished, do not touch the antenna in
the process.
6. The shell surface as far as possible to make 24# spark pattern, grain surface than glossy paste
effect is good, and injection cannot play release agent, spraying to eliminate the antenna area of
the flying oil. For example, the shell flying oil causes the FPC antenna to buckle to produce the
FPC paste smoothly before the shell has oil parts coated with 3367 activators.
7. To ensure the consistency of FPC paste, no positioning column, positioning holes of the
antenna paste, it is recommended to use the fixture positioning assembly.
FPC antenna reliability test requirements
1. testing instruments/ tools: salt spray test chamber, film thickness tester, cotton cloth, gasoline,
abrasion tester, cold and heat shock, constant temperature and humidity chamber, QUV
accelerated erosion tester, colorimeter, imported eraser.
2. FPC antenna design applications: applicable to all wireless network connections that FPC
antenna can use.
C&T RF Antennas Inc provides the PCB antenna design and FPC antenna design service, the
antenna design includes 5G NR FPC Antenna design, 4G FPC Antenna design, 3G FPC Antenna
design, NB-IoT FPC Antenna design, Wifi FPC Antenna design, GPS FPC Antenna design, LoRa FPC
Antenna design, etc. Contact us for more antenna design information you may need.
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5. C&T RF Antennas Inc
https://ctrfantennasinc.com/ https://lcantennas.com/ https://pcbantennas.com/
Please Contact us for more information, thank you.
Contact Person: Coco Lu coco@ctrfantennasinc.com (+86)13412239096
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