T H A N K S F O R A T T E N D I N G OUR. FLEX-RIGID PCBs. Presented by: Nechan Naicker

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1 T H A N K S F O R A T T E N D I N G OUR TECHNICAL WEBINAR SERIES FLEX-RIGID PCBs Presented by: Nechan Naicker

2 We don t just sell PCBs. We sell sleep.

3 Cirtech EDA is the exclusive SA representative of the world s largest PCB supplier Quality PCBs are expensive. Better quality PCBs are even more expensive. But the best quality PCBs are priceless.

4 Why Flex-rigid PCBs? Flex-rigid printed circuits are rapidly becoming the preferred printed circuit board format. Flex-rigid circuits are lightweight, easy to install, durable, compact, and of course flexible. The range of motion can cover 360 degrees, making it the perfect choice for nearly every application.

5 Flex-rigid PCBs are used everywhere. Courtesy of Olympus Courtesy of Nike Courtesy of Teradyne Digital cameras / photocopiers / inkjet printer heads / ABS systems / hearing aids / pace makers / X-ray equipment / mobile phones / GPS / RFID / night vision / laser gyroscopes / surveillance cameras / hard disk drives / DVD players / etc

photocopiers / inkjet printer heads / ABS systems / hearing aids / pace makers /

6 Benefits of Flex-rigid PCBs COST: No need for connectors and cables Reduced assembly costs The whole flex-rigid assembly can be tested in one stage RELIABILITY No field risks caused by loose connectors and cables No assembly risk due to human error High vibration resistance The whole flex-rigid assembly can be tested in one stage PACKAGING No wasted space when PCB area is limited Reduction in size and weight More robust solution

cables No assembly risk due to human error High vibration resistance The whole flex-rigid assembly can be

7 Disadvantages of Flex-rigid PCBs Higher tooling costs due to punch & die jigs Higher material costs Longer leadtime due to construction and profiling Higher moisture absorbtion not recommended for some applications Possible damage due to improper handling More sensitive to scratching Requires strict storage conditions

moisture absorbtion not recommended for some applications Possible damage due

8 Flex-rigid Terminology BASE MATERIAL: Flexible polymer film that forms the dielectric part of the PCB, providing the most primary physical and electrical properties of the PCB. Material types include polyimide, Polyester and a polyester derivative polyethylene naphthalate (PET). COVERLAY: A flexible material that protects and insulates the circuitry on the surface. Aids flexibility and restrains circuitry by preventing it from lifting. Think flexible soldermask. ADHESIVELESS SYSTEMS: Where the copper is bonded directly onto the base material without the need for adhesive. Can operate within higher operating temperature with reduced z axis expansion (less stress on via) and designed as polyimide material.

COVERLAY: A flexible material that protects and insulates the circuitry on the surface. Aids flexibility and restrains circuitry by preventing it from lifting.

9 Flex-rigid Terminology ADHESIVE SYSTEMS: Using epoxy / acrylic / polyimide / polyester adhesives which acts as the medium for bonding copper to the base material. Variations is z axis expansion and therefore ability to operate in higher temperatures. Also risk to via construction. PRESSURE SENSITIVE ADHESIVES: Adhesive films that are added to the PCB (typical flex PCB s) that are either permanent / semi permanent and designed for later attachment to another surface. STIFFENERS: Not an integral part of the flex circuitry, but important to reinforce in localised areas where component assembly takes place supporting assembly process and weight considerations. Typically FR4.

PRESSURE SENSITIVE ADHESIVES: Adhesive films that are added to the PCB (typical flex PCB s) that are either permanent / semi permanent and designed for later attachment

10 Flex-rigid Material Properties

11 Flex-rigid Material Comparison Advantages POLYESTER POLYIMIDE lower cost excellent flexibility at all temperatures Very good tear resistance good electrical properties good electrical properties good chemical resistance lower moisture absorption good tear resistance excellent assembly / thermal performance limited assembly / thermal performance higher cost at lower temperatures it becomes brittle moisture absorption 2% approx. Disadvantages

resistance lower moisture absorption good tear resistance excellent assembly / thermal performance limited

12 Flex-rigid Material Comparison CTE Properties Acrylic CTE ppm/deg C Polyimide FR

13 Flex-rigid Material Comparison Moisture Absorbtion Acrylic moisture absorption % Polyimide FR4 0.00% 1.00% 2.00% 3.00% 4.00% 5.00%

14 Flex-rigid Construction Adhesive System FR4 + Cu + soldermask Coverlay Adhesive Copper clad adhesive material 25µm Adhesive Coverlay 50µm adhesive

15 Flex-rigid Construction Reliability of Adhesive System Problems relate to higher CTE z axis of material around the plated vias and adhesive expansion (key problem) along with rigid to flex bonding with adhesive. Possibility of hole-plating cracks due to increased stresses on the via during the assembly process.

(key problem) along with rigid to flex bonding with adhesive.

16 Flex-rigid Construction Adhesiveless System FR4 + Cu + soldermask Coverlay Adhesive Adhesiveless polyimide core Adhesive Coverlay No-Flow Prepreg

17 Flex-rigid Construction Benefits of Adhesiveless System Use of no flow pre preg (higher Tg) bonding rigid to flex layer (IPC-2223 section ) Reduced z axis expansion through adhesiveless substrate systems (IPC-2223 section ) Limited penetration of coverlay and necessary adhesive into the rigid part does not reach vias - only partial overlap of coverlay (IPC-2223 section )

23 section 5.2.2.2) Reduced z axis expansion through adhesiveless substrate systems (IPC-2223 section 5.

18 Flex-rigid Design Rules Construction Construction style Design with rigid outer layers, and keep the build symmetrical, avoid flex on outer layers. Avoid over complicated constructions Consult with Cirtech EDA for recommended constructions. Consider thickness of flex assembly This will determine the achievable bend radius.

Avoid over complicated constructions Consult with Cirtech EDA for recommended

Flex-rigid Design Rules PCB Design No 90 degree angles / corners in flex part Use drilled holes to terminate any splits in flex to prevent tearing Exit rigid PCB with straight traces with no bends

19 Flex-rigid Design Rules PCB Design No 90 degree angles / corners in flex part Use drilled holes to terminate any splits in flex to prevent tearing Exit rigid PCB with straight traces with no bends Minimise copper weight to allow for flexibility. Cross hatching of large copper areas is preferred to copper fill, again to improve flexibility. Offset tracking for double sided flex parts to improve flexibility

Minimise copper weight to allow for flexibility.

- 6 x circuit thickness Double sided flex - 10 x circuit thickness

20 Flex-rigid Design Rules Bend Radius PERFECT TOO SHORT TOO LONG Some very basic guidelines can be seen below: MINIMUM BEND RADIUS Single sided flex - 6 x circuit thickness Double sided flex - 10 x circuit thickness Multilayer flex - 15 x circuit thickness Dynamic application 20+ x circuit thickness

21 Flex-rigid Design Rules Keepout As per IPC-2223 ( ); PTH s in the rigid section should not be less than 3.18mm plus ½ of the PTH pad diameter from the rigid to flex interface when measured from the PTH centre to the edge of rigid material. 3.18mm + ½ PTH pad diameter > 0.50mm SMD components should be kept at least 0.5mm from the edge at the flex interface to avoid any flatness issue in this area. Preferable to avoid such areas (coverlay overlap) if space permits.

22 Flex-rigid Design Rules Coverlay Openings mm As per IPC-2223 ( ); Partial coverlays of the flexible layers should be overlapped by the rigid sections by 1.27 to 2.54mm. For single sided flex additional consideration shall be given to hold downs to prevent lifting lands. Noting that for double sided flex PCB s the lands normally require filleting or tear dropping.

23 Flex-rigid Design Rules Annular Rings 0.15mm minimum measured against the drilled hole size, preferably more. 0.20mm minimum is recommended for inner layer

24 Semi Flex PCBs Semi flex uses depth-routed FR4 to achieve a flexible / bending section of the traditionally rigid FR4. Whilst rigid flex or flex PCB s are suited to dynamic applications, semi flex is more suited toward static applications or with very limited number of bends.

25 Semi Flex PCBs Using specific grade FR4, the rigid PCB is depth milled to leave a thin section of FR4 and copper this is thin enough to allow flexing of the material Board thickness in rigid part = mm Flexible soldermask Remaining thickness in bend area = 0.25mm ± 0.05mm MIN bend raidus = 5mm

26 Design of Flex-rigid PCBs Consult with Cirtech EDA for design advice Download available guidelines

27 Pre-Assembly of Flex-rigid PCBs We recommend baking of all rigid-flex PCBs, to prevent moisture to migrate into the PCB construction.

29 How may we help you? Cirtech EDA Webinar Series

30 The Last Word Consult Cirtech EDA early - in your conceptual PCB design stage! Specify non-negotiable requirements clearly in the PCB notes, such as BGA impedance control, hole tolerances, etc. Ensure that the manufacturer does not ever change the material or buildup of your PCB, or ever change the factory without consultation. Insist on a Certificate of Conformance and a microsection. Cirtech EDA Webinar Series

31 We have a dedicated team that has pledged to make you our #1 priority. Cirtech EDA Webinar Series

32 Thank you for attending our webinar series. Next webinar: Preparing Clear & Thorough PCB Manufacturing Documentation 11 Feb 11am Cirtech EDA Webinar Series

33 We don t just sell PCBs. We sell sleep. ineedpcbs@cirtech-eda.com eda.com

Flexible Solutions. Hubert Haidinger Director PE/CAM BU Industrial & Automotive 5.June 2013. www.ats.net

Flexible Solutions. Hubert Haidinger Director PE/CAM BU Industrial & Automotive 5.June 2013. www.ats.net Flexible Solutions Hubert Haidinger Director PE/CAM BU Industrial & Automotive 5.June 2013 www.ats.net Austria Technologie & Systemtechnik Aktiengesellschaft Fabriksgasse13 A-8700 Leoben Tel +43 (0) 3842