Page 126 - Microsensors, MEMS and Smart Devices - Gardner Varadhan and Awadelkarim

106 STANDARD MICROELECTRONIC TECHNOLOGIES

Cover film
Adhesive | Etch
firm firm mm nrm
Copper
Adhesive
Base film
Single-sided flex-printed wiring
Cover film
Adhesive
Copper nrm mm mm mm
Adhesive Etch
Base film :> Y///////////////////////////A
Adhesive mm mm mm mm
Copper Laminate
Y///////////////////////////A
Adhesive Double-sided flex-printed wiring
Cover film

Cover film"
Adhesive
Copper
Adhesive mm rmn mm nrm
Base film
Adhesive Etch nrm mrn rmn mm
Copper
Adhesive Laminate
Cover film mm mm mm mm
Adhesive y/////////////////////////zm
Copper Multilayer flex-printed wiring
Adhesive
Base film

Figure 4.43 Schematic cross section of three types of flexible PCBs: (a) single-sided; (b)
double-sided; and (c) multilayered

Table 4.9 Material properties of some resins used in organic PCBs
Units Epoxy Polyimide Cyanate PTFE
ester

CTE ppm/°C 58 49 55 99
Dielectric constant at - 4.5 4.3 3.8 2.6
1 MHz
Poisson's ratio - 0.35 0.33 0.35 0.46
Temperature °C 130 260 260 -
Thermal conductivity a W/m.°K 0.3 0.3 0.3 0.3
Young's modulus GPa 3.4 4.1 3.4 0.03
a
Approximate values
number of different organic materials can be used to make a flexible wiring board such
as polyimide (Kapton), polyester terephthalate (Mylar), random fibre aramid (Nomex),
Teflon, and polyvinyl chloride (PVC). The copper foil is processed as before by optical
lithography, and layers can be joined together to form multilayer laminates. The layers
are usually bonded together using an adhesive such as acrylic, epoxy, polyester, and