This is where we issue the inner layer cores, these are checked for thickness using a micrometer, and for the copper weight using a Elcometer, we then record all Certificate of Conformance Details of the materiel, this is recorded inside the job card.
Fr4 is a generic term for pcb laminate and covers a wide range of laminate types, where the laminate is stated as FR4 the customer has no specific laminate requirements other than a FR4 grade pcb laminate,
FR means “Flame Retardant” and 4 means fiber glass epoxy. This term is used to describe the most popular material to manufacture circuit boards.
Here is some of the detail: FR4 laminate is the usual base material from which plated-through-hole and multilayer printed circuit boards are constructed. “FR” means Flame Retardant, and Type “4” indicates woven glass reinforced epoxy resin. The laminate is constructed from glass fabric impregnated with epoxy resin (known as “pre-preg”) and copper foil, which is commonly supplied in thicknesses of “half-ounce” (approx 18 microns) or “one-ounce” (approx 35 microns). Foil is generally formed by electrodeposition (“ED Foil”), with one surface electrochemically roughened to promote adhesion. A typical 1.6 mm rigid laminate is made by bonding together eight plies of heavyweight pre-preg, with half-ounce copper foil either side, in a hot hydraulic press.
The person issuing the pcb laminate needs to be fully aware of all the stated pcb laminates, flex laminates, prepregs and coverlays.
The simplest way to ensure the correct laminate/material is issued is to tick the requirements, and record what is issued, because of traceability, we need to also record the certificate of conformance details of the laminate/material issued.

Technical Terms for Laminates and prepregs

TG – Glass Transition Temperature; The temperature at which the resin changes from a glass-like state to an amorphous state changing its mechanical behaviour, i.e. expansion rate

DSC – Differential Scanning Calorimetry; A measurement technique used to characterize the glass transition temperature of a resin by measuring the change in heat given off the resin.

TMA – Thermal Mechanical Analysis; A measurement technique used to characterize the glass transition temperature of a resin by measuring the changing in thermal expansion of a resin as a function of temperature.

DMA – Dynamic Mechanical Testing; A measurement technique used to characterize the glass transition temperature of a resin by measuring the change in modulus of a resin as a function of temperature.

TD – Decomposition Temperature; The temperature at which the resin begins to decompose, measured by a weight change the resin sample.

TGA – Thermo-Gravimetric Analysis; A measurement technique used to characterize the decomposition temperature of a resin by measuring the change in weight as a function of temperature.

CTE – Coefficient of Thermal Expansion; The rate of expansion of a laminate as a function of temperature change. Typically reported as PPM/°C or %.

T260 – Time-to-Delamination @ 260°C; A measurement conducted on the TMA apparatus in order to determine a laminate’s resistance to Delamination at 260°C. Delamination is defined as an irreversible expansion in the z-axis. Measurements are noted in minutes at 260°C before failure.

T288 – Time-to-Delamination @ 288°C; A measurement conducted on the TMA apparatus in order to determine a laminate’s resistance to Delamination at 288°C. Delamination is defined as an irreversible expansion in the z-axis. Measurements are noted in minutes at 288°C before failure.

Dk – Permittivity, Relative Dielectric Constant; The property of a material that impedes the transmission of a electromagnetic wave. The lower the relative dielectric constant, the closer the performance of the material to that of air. This property is critical to matching the impedance requirements of certain transmission lines.

Df – Loss Tangent; The property of a material that describes how much of the energy transmitted is absorbed by the material. The greater the loss tangent, the larger the energy absorption into the material. This property directly impacts the signal attenuation at high speeds.

Peel Strength; This measurement is taken to evaluate the adhesion of the resin to the copper cladding, in units of lbf/in or N/m. Measurements are taken after samples have been conditioned in the following manner: as received, after thermal stress, and after chemical processing.

Thermal Stress; This measurement is taken to evaluate the thermal integrity of laminates after short-term exposure to solder, 10 seconds at 550°F (288°C). The samples are evaluated for evidence of blisters and delamination.

TCT – Thermal Cycling Test; this type of reliability test is conducted in order to evaluate a PCB’s resistance to plated-thru-hole failures when exposed to repeated temperatures extremes. Factors in this test that vary from OEM-to-OEM include temperature ranges, time at given temperatures, and medium used to heat and cool the PCB (i.e. liquid or air).

IST – Interconnect Stress Test; an accelerated thermal cycling test that utilizes DC current to heat the PTH and uses forced air to cool the PTH of a PCB coupon. The benefits of using IST inplace of conventional TCT tests include lower cost, failure detection and results within days.

CAF – Conductive Anodic Filament Growth Failure; a PCB reliability issue related to the growth of copper containing filament along the resin-to-glass interface

 

Copper Foil Types

ED= standard shiny copper, copper tooth

HTE= High temp elongation shiny copper, copper tooth

RTF= reverse treat, low profile copper tooth

DT= double treat copper, no black oxide needed

To make the copper foil this is done by the following process

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To make PCB Laminate the laminate supplier takes the required material prepreg and bonds this between sheets of copper foil. Typically this is 36”x48” sheets which are then cut down to the panel size, pcb panel sizes should be 100% utilisation of a 36” x 48” sheet to ensure no wastage.