Design Guidelines - Connectors

DESIGN FEATURES AND CHARACTERISTICS

ZEBRA® connectors are composed of alternating layers of conductive and non-conductive silicone rubber. Contact density of the ZEBRA® connector is greater than the contact pad density of either the LCD or PC board, making it an ideal design choice. When placed between the LCD and PC board at least one conductive layer will connect matched contact pads and at least one insulating layer will isolate adjacent circuits.

PHYSICAL AND ELECTRICAL MEASUREMENTS - NOMINAL

DIMENSIONS

- The above figure shows the dimensions of the ZEBRA® connector. For best overall performance ZEBRA® connectors should be designed with an aspect ratio of H/W equal to or greater than 1.5.

Micro-electronics interconnect packaging applications by their very nature leave a minimum of space in which to assemble mating components. High reliability and very small interconnections, with an everincreasing number of I/O’s, are a must if design objectives are to be met. ZEBRA® connectors can be found in most product types of this nature, and continue to gain wider acceptance as product packages decrease in size. Since each style consists of integral conductors, insulators and selfsupport structures, there is generally no added componentry required for installation – thus a very important by-product of hardware and installation cost-effectiveness can be realized.

AS EASY AS 1...2...3: Using ZEBRA® elastomeric electronic connectors requires only a brief orientation in order to assure that the components provide the finest performance possible. The basic design steps consist of:
1. Layout of your package
2. Select the proper connector and size
3. Design the bezel or retainer

SOLDERLESS CONNECTIONS

Pressure type contact eliminates lead straightening, hole drilling and soldering. NON-ABRASIVE CONTACTS (Zero insertion force) Contact to the LCD is made by deflecting the ZEBRA® connector between the LCD and PC board. ZEBRA® connectors are non-abrasive and will not damage indium oxide contact pads on the LCD. Repeated assembly and disassembly of package components will not affect performance.

ENVIRONMENTAL RELIABILITY

The LCD, when mounted with a ZEBRA® rubber connector, creates a gas tight seal at the contact interface. Assures contact in chemically corrosive atmospheres while at the same time protecting the glass display from shock and vibrations.

SMALL GLASS OVERHANG

With a ZEBRA® connector, LCD terminal overhangs can be as narrow as 0.030”/8mm permitting more efficient use of glass size related to character height. (Metal pins normally require a 0.150”/3.9mm glass overhang, reducing character height by as much as 0.240”/6.1mm for a dual in-line LCD.)

HIGH DENSITY CONTACT

ZEBRA® connectors are available in a variety of contact densities. The most dense allows contact pad spacing as close as 0.010”/0.25mm center-to-center. This spacing can be compared to 0.050”/1.3mm minimum for pins, allowing for increased capacity of LCD formats.

TEMPERATURE RANGE

-55? TO +260? F/-50? C TO +125? C (-60? TO +125? C available on request)

CURRENT CARRYING CAPACITY

40 amps per square inch of contact pad. (0.050A for .035 x .035 pad)

CONNECTION RESISTANCE

Typically 500 to 2,500 ohms.

INSULATION RESISTANCE

Typically 1012 ohms.

DEFLECTION FORCE REQUIRED

1.5 pounds per linear inch for a 0.020” wide ZEBRA®.

LIFE

100,000 hours minimum.

CONDUCTIVE LAYERS

up to 500 per inch.

MECHANICAL - FORCE DEFLECTION

- Recommended deflection is 5% to 25% of the height (H) dimension.
To calculate F (force in pounds) for deflection the following formula may be used:

 

For Carbon ZEBRA®s

Metric:
F = 9 x D x W x L x 9.8x10^-3

Inches:
F = 5806 x D x W x L x 9.8x10^-3

For Silver ZEBRA®s

Metric:
F = 10.0 x D x W x L x 9.8x10^-3

Inches: F = 6452 x D x W x L x 9.8x10^-3

Where: F = Force (N)
H1 = Deflected height of connector (mm or inches)

D =	H - H1
	H

W = Width of connector (mm or inches)
L = Length of connector (mm or inches)
H = Height of connector (mm or inches)

RESISTANCE -

To calculate the resistance of ZEBRA® connectors, choose one of the following formulas:

For Carbon ZEBRA®s

Inches:

R =	2.37 x H	= ohms
	Ew x W

Where:
E_w = Electrode pad width (in)
W = Connector width (in)
H = Connector height (in)

Metric:

R =	60 x H	= ohms
	Ew x W

Where:
Ew = Electrode pad width (cm)
W = Connector width (cm)
H = Connector height (cm)

For Silver ZEBRA®s

Inches:

R=	H x 0.0004	+ 0.10	= ohms
	W x EW

Where:
W = Width of ZEBRA® (in)
E_w = Electrode pad width (in)
H = Height of ZEBRA® (in)
Metric:

R=	H x 0.01	+ 0.10	= ohms
	W x EW

Where:
W = Width of ZEBRA® (mm)
E_w = Electrode pad width (mm)
H = Height of ZEBRA® (mm)

1.1 PRINTED CIRCUIT BOARD DESIGN CONSIDERATIONS

1.2 LCD DESIGN CONSIDERATIONS

1.3 CALCULATING THE SEPARATION FACTORS

Shown at left is a typical LCD-to-printed circuit board interconnect using ZEBRA® elastomeric connectors in a cellular telephone handset. The components are stacked and consist of only three items to be addressed:

Liquid Crystal Display (LCD)
ZEBRA® connector
Printed Circuit Board (PCB)

It is essential that contact mating characteristics be kept as similar to the other components as possible. Any factors restricting positive contact interface should be compensated for in the design. Some of these are as follows:

a.)Registration of contact pads between the LCD and PC board is critical in effecting contact. Contact pads of both should ideally be of the same size and equally matched in tolerances for width and pitch.

b.)Consider carefully PC board thickness and the related flatness tolerances. Proper design should involve the control of “waviness” tolerances and board stiffness. Both elements are essential in the appropriate design and selection of the ZEBRA® connector. Connector deflection and width are important considerations in determining the size of the ZEBRA® connector to be used in order to maintain proper deflection without “bowing” the PC board.

c.)Contact pad material on the PC board, as well as the LCD, should be smooth and regular with thickness tolerances established.

d.)Consider the area on the PC board to be dedicated to the LCD and the presence of neighboring components. Location of the LCD above or on the PC board should permit free clearance on all four sides of the PC board profile of at least 0.250”/6.2mm for packaging and/or fastening.

a.)Select LCD configuration, e.g., Single In-Line (SIL); Dual In-Line (DIL); or contacts on both planes. Example: Dot Matrix.

b.)Select an LCD which in its design has contact pads on the reverse side of the viewing area facing PC board). For those instances where contact pads cannot be stationed facing the PC board, a custom elastomer may be required.

c.)Pitch of LCD contact pads.

d.)Length, width, and thickness of combined front glass and back glass of LCD.

e.)Determine lip width (distance from outside edge of front glass to edge of back glass). This dimension should be at least 0.060”/1.5mm and preferably 0.100”/2.5mm. Ideally, contact pads should extend to the outer edge of the lip on the glass.

Consideration must be given to tolerance control on the elements that comprise the connector package. There are separate flatness and parallelism tolerances for the LCD glass, polarizers, reflectors and PC board. Materials used for the contact pads of the LCD and contact pads of the PC board also have thickness variations which must be considered. Flatness of the PC board and parallelism between the components are also factors. These tolerance values are vital criteria in determining separation variations between the LCD and PC board. The sum of the tolerances of these elements plus nominal separation determine the height (H) of the connector which will meet your design application.

2.1 CONNECTOR PITCH AND LENGTH

2.2 CONNECTOR HEIGHT

2.3 CONNECTOR WIDTH

ZEBRA® elastomeric connectors offer a wide variety of application possibilities, in many cases where no other type of interconnect device is possible. They require a minimum of installation hardware considerations, allowing for very small packaging structures to support low profile display and microelectronic interfacing.

When properly dimensioned, long-life performance can be assured and gas-tight connections without additional precautions can be realized.

a.)Select a ZEBRA® connector that will assure that at least one conductive layer connects between contact pads, for example, of an LCD and PC board to be interconnected, and at least one insulating layer is between adjacent contact pads.

b.)ZEBRA® connectors can accommodate applications with contact spacing of .010”/.254 mm center-to-center or greater. c.) The overall length should extend a minimum of 0.020” beyond the edge of the contact at each end of the connector. a.) ZEBRA® connector height is determined by the separation distance between LCD and PC board contact pads, including tolerance variations. ZEBRA® connectors can be supplied with a height of up to 1”/25mm.

b.) ZEBRA® connector height is the most critical dimension in determining the functional performance of the connected components. Calculate the tolerance stack-up of the PC board, LCD, polarizer, and ZEBRA®. Multiply the maximum separation distance by 1.10 (adding 10% to separation distance) to establish uncompressed ZEBRA® connector height.

c.) The following example shows calculations used in determining uncompressed ZEBRA® connector height.

Example: Separation distance in this application equals 0.200”/5.08mm with tolerance of +/- 0.005”/0.13mm representing the tolerance stack-up from one end of the LCD and PC board separation to the other end. The minimum separation in our application equals 0.195”/4.9mm; the maximum separation equals 0.205”/5.2mm. Multiply the maximum separation of 0.205”/5.2mm by 1.10 to develop the uncompressed ZEBRA® connector height. The resulting 0.225”/5.7mm uncompressed height of ZEBRA® connector is the correct ZEBRA® connector height to assure adequate contact and achieve the minimal 0.195”/4.9mm separation for assembled height of the LCD, PC board package, and to insure contacts in areas where the minimum separation of 0.195”/4.9mm prevails. To achieve the 0.200”/5.08mm assembled height, it is necessary to deflect the 0.225”/5.7mm free height ZEBRA® connector by 10%. The design result falls within the 5%-25% deflection range recommended for effective ZEBRA® connector contact.

a.)Force deflection considerations of the ZEBRA® connector (Refer to Force Deflection formula) result in a recommendation of 0.025”/0.6mm as the width for connectors of lengths between 0.25”/6mm and 2.5”/63.5mm. Continuous connector spans of 2.6”/66mm to 8”/203mm require a minimum 0.035”/0.9mm wide connector to allow easy assembly of the ZEBRA® connector into the slot of a holder. Ideally, the ZEBRA® connector length should be limited to 2.5”/63.5mm due to possible insertion difficulties of the connector in the slot of the holder.

b.)ZEBRA® connectors with a width of 0.025”/0.6mm to 0.035”/0.9mm require the use of a holder. (See design of ZEBRA® connector holder.) Fujipoly offers standard self-supporting ZEBRA® connectors eliminating the need for fabricating a holder for heights up to 0.200”/5.08mm.

3.1 STANDARD SUPPORTED SIZES

3.2 DIMENSIONING A STANDARD OR CUSTOM CONNECTOR HOLDER

3.3 DESIGNING THE BEZEL

Once the ZEBRA® style and design have been decided upon, two last considerations should be resolved; namely:
-Support of the ZEBRA® connector in its operating position
-Application of pressure onto connector height dimension to cause deflection and proper contact to the conductive contact pads.
The most common alternatives are among the following:

A Self-Supporting ZEBRA® connector
A Custom Holder - for your specific configuration
Clamping or fastening devices
he supported connector typically contains a thin elastomeric 0.020”/.51mm wide strip attached to either one or both sides. It is a sponge or solid silicone rubber support medium which allows a lower compression force over a wide range while also providing a greater width-to-height ratio. Thus, the free-standing stance is more stable, especially as compression is introduced.

Carbon and Silver Filled Standard Dimensions (in./mm)
min. max.
width 0.050/1.27 0.157/3.44
height 0.050/1.27 1.000/25.4
length 0.250/6.35 9.000/229.0 carbon; 5.000/127.0 silver

.) Holder/Retainer width: Determine LCD lip width as well as clearance on the PC board allowed to accommodate the LCD.

b.) Holder length: Holder should extend a minimum of 0.1”/2.5mm beyond the edges of the front of the glass of the LCD and/or the PC board pad lengths in order to provide support, and proper positioning and placement of aligning pins of the holder. Where wall thickness of the holder must be thin and length of contact area is in excess of 2.5”/63.5mm, it may be necessary to provide a bridge or separator in the holder slot at 2.5”/63.5mm intervals, or the wall thickness of the frame on either side of the slot must be adequate to inhibit inward “bowing”. Design considerations should preclude such bridges or separators from interfering with the contacts designed to be between LCD and PC board.

The difference between slot width and ZEBRA® width should be approximately 0.005”/0.13mm to allow for easy insertion and removal.

c.) The following design considerations should be evaluated:

Plastic Holders: Reinforced plastic is preferable because it affords superior physical and electrical design properties. Temperature range of LCD should be consistent with temperature specifications of plastic selected. Chamfer the slot in the holder as shown in the illustration. Add 0.005”/0.13mm to the width of the slot for insertion of the ZEBRA® connector. Allow a minimum of 0.050”/1.3mm wall thickness or greater as height approaches 0.150”/3.8mm/ Locating pins should be molded to bottom of ZEBRA® connector holder to provide registration between LCD and the PC board contacts. See Figure #1.

Metal Holders: In designing metal holders, specify an insulating barrier or supports on the sides of the ZEBRA® connector to assure electrical insulation to eliminate shorting, etc.

Locating pins: Should be provided on the ZEBRA® connector holder to provide registration between LCD and PC board contacts. Check with the LCD manufacturer regarding the glass seal in designing either plastic or metal holders. Provide room in the ZEBRA® connector holder for the seal. Provision should be made to accommodate loose polarizers and reflectors if such elements are included in the design.

In determining design requirements for the bezel, specific design elements should be considered:

a.)Using separation distance factors, determine required height of the bezel. Length and width of the LCD plus holder tolerances will establish length and width dimensions.

b.)Must the LCD be protected? If so, the bezel should incorporate a cover element.

c.) Is sealing required to prevent dust and/or moisture intrusion? Under what environmental conditions will the LCD be expected to function?

d.)What is the LCD viewing area? Be sure that bezel edges do not interfere.

e.) Is masking required for any portion of the LCD viewing area?

f.) Can the housing or case of the end product be used to provide the necessary pressure and protection required for the LCD/PC board connection? If so, a bezel may not be necessary.

g.)Will there be a need for clamps or fasteners? Consult Fujipoly as a design reference source for bezel configurations.