This document discusses using laser direct structuring (LDS) antennas for hearing aids. LDS can embed conductive patterns directly into plastic parts during molding. This allows hearing aids to be designed with integrated antennas rather than manually mounted flexible printed circuits, reducing assembly complexity. The document presents a prototype hearing aid designed with an LDS antenna embedded in the plastic frame for simplified assembly. Testing showed satisfactory solder joints could be made to the LDS antenna and that the process provides advantages like increased design freedom, size reduction, and simpler recycling of plastic components.

1. Project Plastic – November 29th 2018
Nicolai Domingo Nielsen
Feasibility study of Laser Direct Structured (LDS) antennas
for Hearing Aid applications

2. DTU Mechanical Engineering, Technical University of Denmark
Modern electronic devices
2
Exploded
view
Microphones
Antenna
Amplifier
Chipset
Battery
Telecoil
Shielding
Volume buttons
Speaker
Modern complex devices = Many connections

3. DTU Mechanical Engineering, Technical University of Denmark
Laser Direct Structuring (LDS) & Moulded Interconnected Devices (MID)
3
Examples:
Substrate
(λ = 1064 nm)
(e.g. Ultrasonic)
(protects from corrosion)
12-18 μm
2-4 μm
min. 0.1 μm
(Barrier and bonding layer)
Process:
of polymer

4. DTU Mechanical Engineering, Technical University of Denmark
Bionic Ant example
4

5. DTU Mechanical Engineering, Technical University of Denmark
LDS antennas for hearing aids
• Today: Flexible Printed Circuit (FPC) 2.4 GHz antenna.
- Manually mounted.
- Placement tolerances.
- Assembly complexity.
- 3D constraints.
5
jig:

6. DTU Mechanical Engineering, Technical University of Denmark
Design process – Interconnection:
6
• Press fit pins:
• Pogo pins:
• Spring clips:
min.
2mm
min. 4mm
[2]
[3]
[4]

7. DTU Mechanical Engineering, Technical University of Denmark
Chosen design solution with LDS
7
Speaker is
mounted to the
lower part of
the frame, and
connected
through red
wire.
P
C
B
ALDS
antenna
Soldering
P
C
B
A
LDS-
grade
polymer
Regular
polymer

8. DTU Mechanical Engineering, Technical University of Denmark
Final prototype
8
Frame:
Assembly:
Material: PA 4T
30% glass reinforcement
Soldering

9. DTU Mechanical Engineering, Technical University of Denmark
Tests and results – Corrosion and soldering on polymers.
9
320 ºC – Solder
joint cross section:
Satisfactory solderings
for 300ºC and above.
Thicker lines can
increase corrosion, by
increased roughness.
Cross section of LDS line:
Dark areas show corrosion in the
beginning of the nickel layer, and
the blue are related to the copper.
Synthetic ear wax:

10. DTU Mechanical Engineering, Technical University of Denmark
More advantages with LDS
10
Thank you
• Increased mechanical design
freedom for plastics with LDS.
• Size reduction: up to 920 μm in the
width of an hearing aid.
• Recycling of plastic with a simple
separation process by turbulence.