Wiring, Printed - Component
The devices covered under this category are incomplete in certain constructional features or restricted in performance capabilities and are intended for use as components of equipment submitted for investigation rather than for direct separate installation in the field. THE FINAL ACCEPTANCE OF THE COMPONENT IS DEPENDENT UPON ITS INSTALLATION AND USE IN EQUIPMENT SUBMITTED TO UL
Minimum Cladding Conductor Width — The minimum width of any conductor spaced more than 0.4 mm from the edge of the printed wiring board.
Minimum Edge Cladding Conductor Width — The minimum width of any conductor parallel with and not spaced more than 0.4 mm from the edge of the printed wiring board.
Cladding Conductor Thickness — The minimum metallic cladding thickness of the conductor. The cladding thickness represents the copper conductor thickness only, unless otherwise noted.
Number of Clad Sides — Indicates whether the printed wiring boards have a pattern on one side (denoted as single sided [SS]) or on both sides (denoted as double sided [DS]).
Maximum Area Diameter — The maximum unpierced conductor area of a printed wiring board is judged by the diameter of the largest circle that can be inscribed within the pattern.
Solder Limits — Unless designed for hand-soldering only, each printed wiring board construction is assigned a maximum temperature and dwell time. The tabulated levels are the maximum temperature and cumulative time conditions to which the boards may be subjected during assembly of components. Multiple solder limits are used to represent surface-mount technology (SMT) soldering process maximum temperature and time profiles.
Maximum Operating Temperature — The maximum continuous-use temperature to which the printed wiring board may be exposed under normal operating conditions in the end product .
Flammability Classification — Processed printed wiring boards with or without applied coatings, finishes, etc., as supplied to the device or appliance manufacturer, may be classified based on burning tests conducted in accordance with ANSI/UL 94, "Tests for Flammability of Plastic Materials for Parts in Devices and Appliances," at the option of the manufacturer.
Where such testing has been conducted, the printed wiring board is classified as HB, V-0, V-1, V-2, VTM-0, VTM-1 and/or VTM-2 .
Conductor Finishes — Metallic plating on conductors, contact fingers, plated thru-holes, etc., may be tested at the option of the manufacturer.
Direct Support of Current-carrying Parts — A printed wiring board that meets the minimum ANSI/UL 796, "Printed-Wiring Boards," levels of direct support of current-carrying parts is identified to enable the OEM to select appropriate printed wiring boards for use in products. Direct support is not investigated for "Flammability Only" boards and should be considered during the end-product investigation.
The required performance levels are shown below:
PERFORMANCE PROFILE LEVELS OF BASE MATERIAL OF PRINTED WIRING BOARDS
THAT PROVIDE DIRECT SUPPORT OF CURRENT-CARRYING PARTS
Volume resistivity - dry
Min meg-ohm cm
Volume resistivity - wet
Min meg-ohm cm
Dielectric strength - dry
kV per mm
Dielectric strength - wet
Comparative Tracking Index
# Testing is intended to be as described in ANSI/UL 746A, "Polymeric Materials - Short Term Property Evaluations."
+ Test sample thickness on which the index is to be based.
@ Actual thickness or minimum thickness of material being considered.
* Not required for thermoset; for thermoplastics, at least 10°C (18°F) above rated operating temperature with 90°C (194°F) minimum value.
Comparative Tracking Index (CTI; ASTM D3638 ) — Expressed as that voltage which causes tracking on a printed wiring board base material after 50 drops of a 0.1% ammonium chloride solution has fallen on the material. CTI is not investigated for "Flammability Only" boards and should be considered during the end-product investigation.
CTI Range-tracking Index (TI in Volts)
600 and greater
400 and up to 600
250 and up to 400
175 and up to 250
100 and up to 175
Less than 100
The CTI Performance Level Category (PLC) of a printed wiring board is dependent on the CTI PLC of the base material used to make the board. The CTI PLC may be identified to facilitate OEM selection of printed wiring boards for applications in which the CTI rating is significant.
The above electrical properties may be determined by means of the applicable ASTM and/or UL specification in ANSI/UL 746A.
CONDITIONS OF ACCEPTABILITY
Unless specified otherwise in the individual Reports, consideration is to be given to the following Conditions of Acceptability when these components are employed in the end-use equipment:
1. Printed Wiring Board Identification — The printed wiring board is identified in accordance with the UL MARKING requirements noted below, and it can be determined that the part is made from the material specified.
2. Pattern Limits — The narrowest conductor width shall not be less than the indicated minimum width mid-board or edge conductor depending upon operating temperature conditions, as indicated in the end-product Report. "Flammability Only" boards are not investigated to determine the minimum acceptable conductor widths, maximum area conductor diameter, and/or the silver conductor limitations, and shall be considered during the end-product investigation.
3. Conductor Maximum Area Diameter — The maximum area diameter of conductors shall not be greater than the indicated maximum.
4. Conductor Thickness — Thickness or weight of conductors shall not be less than the indicated minimum.
5. Silver Conductors — The minimum spacing between any two silver conductors of different potential must not be less than that indicated. The silver conductors have been found suitable only for circuits that do not require a dielectric strength potential greater than that indicated between adjacent parts and conductors. "Flammability Only" boards are not investigated to determine if silver conductors are present on the board, and the effect of silver conductors on the board shall be considered during the end-product investigation.
6. Solder Limits — The temperature and dwell-time exposure during wave, flow, dip or an equivalent soldering operation for assembly-soldering processes shall not exceed the indicated maximum. The maximum dwell time is the cumulative time for all soldering operations when the soldering is done in different steps. During SMT soldering, the temperature and dwell time of each reflow zone shall not exceed the indicated maximum multiple solder-limit steps. The solder-limit temperature and dwell times do not apply to hand-soldering.
7. Maximum Operating Temperature — The maximum operating temperature of the metal-clad material shall not exceed the indicated maximum. The maximum operating temperature is not investigated for "Flammability Only" boards and shall be considered during the end-product investigation.
8. Flammability Classification — The flammability classification, with consideration to solder limits during the assembly process, shall comply with the flammability level acceptable for the applicable UL end-product standard. Coatings shall not be employed unless so indicated in the specified process. If the board assembler or end-product manufacturer applies any coating, the effect of the coating on the flammability of the board shall be determined in the end product.
9. Voltage Rating — No voltage rating is assigned. The suitability of the base material as insulation between live-metal parts and dead-metal parts shall be determined in the end product.
10. Minimum Spacing — Minimum required spacing between conductors of different potential and between these conductors and dead-metal parts. Cupping, twisting, bowing and/or warping of the board has not been investigated.
11. Minimum Dielectric Thickness — Minimum required dielectric/insulation thickness (distance through) between conductor layers has not been investigated regarding dielectric strength requirements in the end-product design.
Additional Conditions of Acceptability may be included in the Report available from the manufacturer.
COLUMN HEADING ABBREVIATIONS
The following abbreviations or symbols are used in the column headings in the individual Recognitions:
Double or single sided
Max Area Diam
Maximum Area Diameter
Max Oper Temp
Maximum Operating Temperature
Minimum Edge Conductor Width
ANSI/UL 94 Flammability Classification
Direct Support of Current-carrying Parts
Comparative Tracking Index
A triangle symbol is marked on those products within a given type designation that comply with direct support of current-carrying parts performance level requirements of ANSI/UL 796. "All" is used to indicate that all base materials under that type designation comply with direct support of current-carrying parts performance level requirements of ANSI/UL 796.
The CTI PLC rating of a printed wiring board may be marked on the board or a CTI rating may be assigned to a type designation.