Polyflex-circuits

Wiring was yesterday, Polyflex is state-of-the-art

What is a Polyflex-circuit? What are the unique features of Polyflex-circuits?

Polyflex is the general identifier for single layer flexible circuits, usually consisting of a 250 µm to 300 µm thick copper layer which may also be partially uncovered on both sides. This means that in these areas there is an absence of carrier foil as a base material, which is the main difference to conventional flex circuits.Accordingly the copper layer may be partially bare, whereby any shape of holes and openings is possible,Flexibility in parts of the Polyflex circuits is achieved by reducing the copper thickness in the flexible parts to 100 µm or less.

The connection of normal flex circuits to conventional printed circuit boards requires the soldering of ade-quate connectors. As a result of the thick copper layer (250 µm to 300 µm), Polyflex already provides ade-quate connectivity. The thickness is comparable to that of normal IC connecting pins, thereby Polyflex circuits can be soldered directly. Naturally components can be assembled directly to the Polyflex circuits. Another great advantage of Polyflex is its high current carry-ing capability, while being flexible. 250 µm thick cop-per tracks are already capable of carrying high cur-rents, which could not be achieved on any conventional printed circuit board (e.g. on a 5mm wide and 250 µm thick copper track, 10 amperes can flow, while the track temperature increases only about 10° Celsius). Refer to Current load diagramm.

Example of a Polyflex circuit with high-current tracks, stan-dard signal tracks leading out to free copper pins.

Basic construction of a Polyflex-circuit

To clarify the application possibilities the sketch below illustrates a cross section of the copper layer, indicating a reduction in thickness from approx. 250 µm to ap-prox. 100 µm - 120 µm:

Polyflex - a Neuschäfer product!

„Offer advantage - reaping the rewards“, this is the basic motto of our company. With the development of Polyflex circuits a product has evolved in our company with which we can provide our customers with cost ef-fective and technological advantages.

Wilfried NeuschäferJuly 2008

PolyimideAdhesive

250 µmCopper

100-120 µmCopper

Solder joint

Polyflex bending characteristics

Conventional flexible circuits provide essentially better characteristics concerning enduring bending cycles than Polyflex circuits. During the exact analysis of bending characteristics of Polyflex circuits initially we need to differentiate between the approx. 100 µm thick flexible part and the transition area from the 100 µm to 250 µm copper thickness on the contact fingers. The following test was carried out: Tumble-Bend-Test with a bending radius R = 5 mm, 100 cycles/min with parallel 100 µm thick copper tracks. After aprrox. 10,000 bending cy-cles first hairline cracks appear visible on the surface,however these did not lead to electrical failure, the latter occured only after over 150,000 cycles. The transition area from 100 µm to 250 µm copper thickness can ob-viously not be designed for maximum flexibility, but in that area practically no enduring bending is performed.During a 180° deflection test, over a bending radius of 2mm and a tensile load of 3.93 Newton on the kink, the electrical failure of the copper tracks occured after approx. 150 cycles. These results clearly indicate, that the bending characteristics of Polyflex are more than adequate for all requirements and situations during as-sembling, processing as well as servicing.

Polyflex circuits usually have a copper thickness of 250 µm to 300 µm in the rigid part and 100 µm copper in the flexible part. These single sided copper tracks are embedded in a Polymide film. Several areas of the Po-lyflex cicuit can also be strengthened with FR-4 materi-als (e.g. multi pin connector applications). The exposed copper surfaces are normally galvanically coated with a PbSn-layer or at the customers request can be hot air levelled (HAL).In addition an adhesive layer can be applied to the cir-cuit, which is covered with a protective foil. On custo-mer demand the contact fingers can be supplied alrea-dy bent according to existing standard bending layouts provided by us.

Our production provides the suitable tools for the most current grid dimensions.

Implementation forms of Polyflex - circuits

straight contact pins 90° bend vertically mountable with staggered grid

flat mountable with staggered grid

Contact strip with bended connector pins

Surface circuit with bend pins in staggered grid

Two Polyflex circuits in delivery panel

Special forms of Polyflex - circuits

The normal single layered Polyflex circuit can be en-hanced to a double layer, plated-through version. In this case only one layer features the Polyflex specific cha-racteristics, while the second circuit layer is equivalent to a conventional flexible circuit with 35 µm or 70 µm CU-thickness.

With copper shield layer

Vibration security

Connector

free side

free side

Connector

Rips

Basically soft materials do not incline to natural oscilla-tions as much as rigid boards. If one leads a damped oscillation on a Polyflex circuit, this moves in the same tact like the impulse, exactly as the oscillation genera-tor. Conditioned by the adaptable construction form of the Polyflex circuits a phase displacement is generated, resulting in a damping of the oscillation amplitudes.The size of the phase displacement is dependent on the sym-metry of the circuits.

Lengthwise ribs fundamentally lead to the oscillation damping. In the ideal case there is a mechanical stabili-sation in both head sides by which additional damping is reached. The circuit symmetry of most Polyflex circuits corresponds to these basics:

Double layer Polyflex technology

Additional flex layer for signal traces

Oscillation production by acceleration with different means of transportation

52 5 2 5 2 Hz10 0 10

110

2

f

- 1Grundpegel

- 2 Spitzenwerte

Flugzeug

LKW

Eisenbahn

Schiff

0

0

0

0

50

100

150

200

50

20

10

a

a

a

a

m/s2

m/s2

m/s2

m/s2

1

2

1

2

1

2

Ship

Railroad

Truck

Plane

2 peak value1 base value

Partial view of our punch department

Our special punching technique for Flex and Polyflex circuits

By internal development of a CNC-punch unit we are able to reduce our tool costs. Our production objective is to always provide our customer with a competitively pri-ced product, featuring maximum benefits. This requires optimal process planning and constant upgrading. In particular the production of Flex circuits and Polyflex circuits demands our expertice. The series production usually depends on the requirement of expensive pun-ching tools, which punches multiple components on one panel at the same time. Our in-house developed con-cept is based on a single die punch system, on a CNC controlled machine, whereby each of the Polyflex cir-cuits on a panel are individually punched in succession.This on the one hand prevents any contour variations by using the same punching tool and on the other hand provides the client with a cost effective tooling, for stan-dard production.

Bottom (Cutting template)Top (Plunger)

Example of contour tools of subsequent cuts:

Automated puncher with electronic centering

Special form of Polyflex circuit: additional shield layer

Polyimide foil

Cu-250 µm

Cu-35 µm(e.g. as shield layer)

Isolation layer

Polyimide foil

Interdependence of temperature rise of tracks on current and track width with a copper strength of 250 µm.

Polyflex Current load diagramm Conceptional examples of Polyflex-circuits

Application examples of Polyflex circuits for easy and secure connection of multi point connectors to printed circuit boards:

Sensor

Assembled PCB

Open recumbentcopper connections for soldering on to a PCB

Reinforced Polyflexcircuit with hole pattern of multi pin connector

Multi pin connector

A multi point connector is connected to a sensor electronic:

Stro

mst

ärke

in A

mpe

reC

urre

nt

Current load diagram

track widthCopper thickness

Rise

of t

rack

tem

pera

ture

Assorted sample boards can be requested at any time free of charge.

Technical data/ Specification*

Required manufacturing tolerance:

Between individual contours ± 0.10 mmcontour to track (step & repeat punching) ± 0.15 mmcontour to track (panel cut / band steel cut) ± 0.25 mmlength of the contact fingers ± 0.40 mmparallelism of the contact fingers (bend) ± 0.30 mmLayer misalignment ± 0.13 mmmax. partial size with low cost step & repeat punching 100 x 100 mmmax. possible partial size with manual punching 400 x 300 mm

Etching tolerance:

Width of the contact fingers + 0.20 mm / - 0.10 mmhole diameter ± 0.13 mmtrack width + 0.20 mm / - 0.10 mmcopper thickness (flexible part) ± 0.025 mm

Image:minimale track width / distance 0,40 mm/0,40 mm

Surfaces:galv. Sn / Pb, galv. Pure tin 0,012 mm plus 100 % (+3 µm/-6 µm of copper)Hot - Air - Leveling (HAL) layer thickness covers to 0,040 mmgalv. Ni / Au, chem. Ni / Augalv. Ni/Au, chem. Ni/Au

tensile strength from 250 to 300 N / mmBrinell hardness standard HB 75 ± 5, Hard 95 ± 5

Base copper:Standard 0.25 mm thick, in accordance to DIN 40500 material characteristics in accordance to DIN 1787 (ECu 57)

Copper thickness/ tolerance:

0.25 + 0.00 mm / - 0.03 mmflexible area 0,120 ± 0,025 mm

Cover foil:

Standard 0,025 mm Polyimide with 0.05 mm adhesivea part of the cover foils is UL-listed (Flammability Class)

* Divergent values can be partially agreed upon arrangement

© b

y ne

-cen

tral s

ervi

ces

2008

Neuschäfer Elektronik GmbH Siegener Str. 46D-35066 Frankenberg/ EderMo-Fr von 8:00 bis 17:00 Uhrfon +49 6451 23003-0 fax +49 6451 23003-50mail office@neuschaefer.dewww.neuschaefer.de

• Flexible• High current load• Direct mountable• Vibration security• Reflow capable• Cost-reducing

Construction according to customer specifications. The project is prepared on our CAD system.

Image of a Polyflex Circuit boards developed and produced by us.

Polyimide foil

double-sided freesolder joint

presice assem-bly contour

Friccontact fingerwith 300µm Cu

Details Examples of assorted Polyflex Circuit boards