1. Field Of The Invention

This invention relates to an improved backup board, a method for its manufacture, and particularly to its use in the fabrication of printed circuit boards.

2. Background Of The Invention

The microelectronic industry has undergone a revolution over the last few years. This revolution has been driven largely to meet an explosion in consumer demand for smaller and cheaper applications and combined with the advent of second and third generation telecommunication technology, the desire for increased functionality.

The ubiquitous cell or mobile phone is a readily identifiable example of a microelectronic device where substantial down-scaling has taken place. Today, cell phones consist of about 8 to about 14 Integrated Circuits having a total active device area of 3cm2' Cell phones have shrunk from about 20cm and a weight of about 170grams in 2000 to less than 8cm and a weight of 80 grams in 2003. The demand for smaller applications requires that semiconductor chips, the devices' engines, must themselves be fabricated having smaller dimensions. New processes allowing for their fabrication also need to be explored.

In the past much of the prior art has focused on the semiconductor wafer and its composition. Although wafers are now designed which are considerably smaller and more reliable than their predecessors little energy has been directed towards the drilling processes and materials involved in the early stages of Printed Circuit Board (PCB) manufacture. The microelectronics industry now frequently uses circuit boards having drill holes that are 0.1mm to 0.3mm or even less.

Limitations inherent in existing methods, require new and innovative manufacturing techniques to successfully meet both the industry demands and to reduce assembly losses resulting from damage to individual components. Some of the assembly losses occur as a consequence of incorrect drilling caused due to warping, insufficient surface hardness of presently used backup boards, resins built up from powdery residues left after the hole has been drilled and burring resulting from backup board deformation or drill clog. The quality of the drill hole is a feature paramount in the manufacture of a printed circuit board. The quality of a through-hole drilled in a circuit board is measured by its ability to support and accept the plating and soldering operations required to form a highly reliable, non-degrading electrical and mechanical connection. When circuit boards had traces on only one side, the quality of the drilled hole was not very important. Later as double-sided boards with plated through-holes became common, drilled through-hole quality needed improvement. Since today's multilayer boards require connections to the inner layers as well as the surface pads, the quality of the drilled through-hole is essential in ensuring reliable connections.

The present inventors have recognized that existing practices no longer meet the microelectronic industry needs. As noted earlier, the circuit board fabrication industry is experiencing rapid technological change. The driving force behind these changes has been the increased use of surface mount technology (SMT) and the consequent need for designers to maximize the use of board real estate. Consequently, the industry has experienced increases in the number of holes per square inch, smaller SMT pads, conventionally drilled vias as small as 0.0039" (0.1mm), increased layer counts, tighter annular rings, as well as blind and buried vias. There is no manufacturing area where these changes have had more of an impact than in the drill room.

The root cause for a big percentage of all circuit board failures can be traced back to drilling. When the entire board manufacturing process is examined, it becomes apparent that many post- drilling operations are corrective measures designed to overcome shortcomings in the drilling process. For example, the use of mechanical scrubbing to remove burrs, chemicals to remove resin smear and bonded debris, etch-back to expose glass fibers, and acid or alkaline cleaners to remove contaminations all are methods for addressing problems that result from the drilling process.

Generic drilling practices are no longer acceptable. Industry specific drilling process need to be developed and validated for each unique type of board technology. A key concern in the change of mindset from applying generic drilling practices to tailoring a specific and unique process for each technology is the selection of consumables used in the drill room.

Historically, cost alone determined the selection of consumables used in the drill room. However, as technology continues to push the drill room for improvements, the role of consumables can no longer be overlooked. To remain competitive, circuit board manufacturers have had to develop a unique set of processing parameters for each type of printed circuit board. As is often the case when conventional thinking is challenged, innovative fabricators have been rewarded with greater efficiencies, improved yields and reduced costs.

Although there are many items on the consumables list in the drill room, the three most important are: Drill bits Entry materials and Backup materials.

The present invention is directed to new backup materials and to the processes in which they are put. Most defects commonly related to drilling when using the wrong backup materials are: Nailheading: The distortion of the copper inner layer at the hole wall, this distortion takes the form of a "nailhead". There are several types of nailheads, one of the more common types is Mechanical nailheading. Mechanical nailheading is characterized by a one directional nailhead. This nailheading is usually accompanied by a heavy resin smear over the copper or some types of backup material adhere to the drill bit flutes causing hole wall quality problems. Smear. Resin transferred from the base material of the hole wall during drilling covering the exposed edge of the inner layer pad (land). There are two types of resin smear, nailheading, and the thermal mechanical smear that is created by excessive heat and is clear in appearance. The mechanical smear is heavy coating over the inner layer land with a colour similar to the resin system being used. The main reasons related to backup material are: a) Undercured resin or thermoplastic material used in the backup board, and b) Drill depth into the backup material when the thickness tolerance is out of the range. Resin fracturing (haloing) surface: Damage to resin in the proximity of the drill-hole wall. The damage may be "surface" or "hole wall fractures". Surface fractures are visible without the aid of cross sectional analysis, and will usually be accompanied by disruption of the outer layer copper material. Drill-hole wall fractures occur between conductor layers and usually require cross sectional analysis for detection. Surface fractures may be caused by the wrong type of backup material used (too soft). If the backer material does not support the PCB properly on exit- the material will be pushed out instead of drilled, creating an exit burr which will usually shows as fractures under the copper. Drill-hole wall fracture may be caused when the drill flute clogs with resin or thermoplastic materials in the backup material. Gouging: Excess and irregular removal of base material from the drill- hole wall. Gouging may be evident in the resin rich area and is caused by too deep a drill depth into the backer material. It is often a result of an unsuitable thickness tolerance of the backup material. Burrs (exit). The distortion of copper foil on the outer layer(s) of the PCB. Burrs may be either entry or exit burrs, and may be visible on both sides of the same panel. Exit burrs may caused by the backer material being too soft or may be due to the drill bit flute clogging with backer material.

Selecting the appropriate backup material is important to the drilling stage in PCB fabrication. The purpose of the backup material is to prevent exit copper burrs on the underside of the drilled stack and to provide adequate space for drill stroke termination.

Surprisingly, the backup materials of the present invention have been found to provide for a backup board having properties such as excellent "through-hole" drilling, thickness and dimensional stability characteristics. The composition of the backup board does not contain abrasives that would increase drill wear or contaminates that could block the drilled hole and the surface. Consequently, the backup boards are smooth to the drill and have a hardness sufficient to suppress exit burrs. The backup boards of the invention are ideally, although not exclusively, suited for use in Printed Circuit Board fabrication. Additionally, the backup board component materials are preferably biodegradable and recyclable. The backup boards are relatively inexpensive to manufacture and offer a desirable alternative to existing materials.

3 Objects Of The Invention

It is an object of the invention to provide a backup board which will go some way towards obviating or minimizing the aforementioned disadvantages, or one which will at least provide the public with a useful choice.

4. Statement of the Invention.

Accordingly, in its broadest aspect the invention provides for a backup board material suitable for use in PCB fabrication, which comprises a plastic, cellulosic composite. Accordingly, in a second aspect the invention provides for a backup board material suitable for use in PCB fabrication, which comprises a recyclable, plastic, cellulosic composite.

Preferably, the backup board material is biodegradable.

Preferably, the backup material comprises as a major component one or more cellulosic material(s).

Preferably, the backup material comprises about 10 to about 90% of the one or more cellulosic material(s).

Preferably, the cellulosic material(s) has a moisture content of less than 60 %, preferably 20%, and most preferably the moisture content ranges from about 5% to about 15%.

Preferably, the cellulosic material(s) has an average particle size of less than lOOOμm, most preferably the average particle size ranges from about lOOμm to about 500μm.

Preferably, the cellulosic material(s) is selected from natural fibres such as paper, cardboard, packaging, rice chaff, husk, bamboo, bagasse, straw, sawdust, wood flour, coconut fibre, jute, and the like or a mixture thereof.

Preferably, the backup material further comprises a natural thermoplastic biopolymer, or a natural starch such as maize, corn, rice, soya, cassava, semolina, yucca, and the like, or a mixture thereof.

Preferably, the backup material further comprises about 0.01% to about 50% of a thermoplastic biopolymer or natural starch, or a mixture thereof.

Preferably, the thermoplastic biopolymer or natural starch has a moisture content of less than 20 %, and most preferably a moisture content of from about 5% to about 15%.

Preferably, the thermoplastic biopolymer or natural starch has an average particle size is less than 2000μ, most preferably the average particle size ranges from about lOOμ to about 1400μ.

Preferably, the thermoplastic biopolymer or natural starch has a fat content of less than 5%, and most preferably a fat content of from about 0.8% to about 1.0%. Preferably, the backup material still further comprises natural resins, environmental-friendly additives or other plastic polymers.

Preferably, the backup board material comprises from about 0.01% to about 90% of a natural resin, environmental-friendly additives or other plastic polymers.

According to a third aspect of the invention there is provided a backup board material suitable for use in PCB fabrication which comprises a plastic, cellulosic composite characterized in that the material comprises: (i) from about 10% to about 90% of one or more cellulosic material(s), (ii) from about 0.01% to about 50% of a thermoplastic biopolymer or natural starch, or a mixture thereof, and (iii) from about 0.01% to about 90% of a natural resin, environmental-friendly additives or other plastic polymers.

Preferably, the backup board material is recyclable.

Preferably, the backup board material is biodegradable.

Preferably, the backup boards according to aspects one, two and three are obtained via an extrusion process.

Preferably, the backup board according to aspects one, two and three is an extruded, plasticised, homogeneous, degassed wood/polymer composite.

Preferably, the thickness of the backup board according to aspects one, two and three is from about 0. lmm to about 5mm, and most preferably from about lmm to about 3mm.

A fourth aspect of the invention provides for a method of preparing a plastic cellulosic backup board suitable for use in PCB fabrication, the method comprising the steps of: (i) pre-treating the backup board starting components comprising: (a) one or more cellulosic material(s), (b) a thermoplastic biopolymer or natural starch, or a mixture thereof and (c) a natural resin, environmental-friendly additives or other plastic polymers such that they are in a condition suitable for blending, (ii) blending, and optionally compounding, agglomerating or wood palletizing, the components treated at step(i) in a desired quantity and for a time, heat and pressure sufficient to enable them to be extruded (iii) extruding the blended components to ensure a melt is obtained, (iv) sizing and/or tooling the melt to a desired shape and/or a desired thickness (v) optionally cooling the appropriately shaped and sized melt to a temperature sufficient to facilitate cutting and (vi) cutting the prepared melt into a predetermined length.

Preferably the starting components are blended in the following quantities: (i) from about 10% to about 90% of one or more cellulosic material(s), (ii) from about 0.01% to about 50% of a thermoplastic biopolymer or natural starch or a mixture thereof, and (iii) from about 0.01% to about 90% of a natural resin, environmental-friendly additives or other plastic polymers.

Preferably, the extruder used is a conical twin screw extruder.

Preferably, the backup board obtained is an extruded, plasticised, homogeneous, degassed wood/polymer composite.

Preferably the thickness of the extruded, shaped and/or sized melt obtained at step (iv) is from about 0.1mm to about 5mm, and most preferably from about lmm to about 3mm.

Preferably, the method is directed to a continuous or "one-pot" procedure.

A fifth aspect of the invention relates to the use of a backboard according to the first, second or third aspect of the invention or as manufactured according to the fourth aspect of the invention in the manufacture of a PCB.

A sixth aspect of the invention relates to a PCB whenever manufactured using a backup board according to according to the first, second or third aspect of the invention or as manufactured according to the fourth aspect of the invention 5. Brief Description Of The Drawings

The invention will now be described by way of a non-limiting example only and with reference to the accompanying drawings in which:

FIG. 1 illustrates the process of events as the material passes through a conical twin screw extruder

FIG. 2 depicts graphically comparative residence times of material as it passes through an extruder. The comparison is between a conical twin screw extruder and a standard twin screw extruder.

FIG. 3 is a flow chart outlining preferred process steps.

Appendix A provides preferred final product specifications.

6. Description Of The Invention

One of the key process steps in the manufacture of PCB 's is the drilling step. It is at this phase of the process that most waste occurs. The purpose of the drilled through-hole is to make an opening through the printed circuit board that: (a) Permits subsequent processes to make an electrical connection between top, bottom and all internal pathways, and (b) Allows through-hole components to be located precisely and mounted with structural integrity.

The term backup board is intended to cover the US equivalent term backer board. That is, the terms may be used interchangeably.

Present PCB manufacturing techniques require the drilling of drill holes with diameters of from 0.1mm to 0.3mm. The industry demand to have even smaller drill holes and therefore more circuitary per sq cm of board is inexorable. In drilling the PCB 's backup boards are used to prevent damage to the drill bits. The backup boards presently used are expensive and can be used only twice. Once the first drilling is completed they are flipped and a second drill may be made. The backup board is then discarded. It is impracticable to recycle existing backup boards, many of which contain toxic or undesirable components. The mountain of used backup boards are an increasing environmental problem and one which is seen to be a costly one. Local and governmental agencies worldwide view these waste materials as being unacceptable may legislate against or tax their use resulting in extra costs to what is already a highly competitive industry

7. Detailed description of a Preferred Embodiment of The Invention In a preferred embodiment, the present invention provides for an improved backup board wherein conventional backup materials used in the PCB drilling process are replaced with recyclable, biodegradable materials made by a novel extrusion process.

Although there are many items on the consumables list in the drill room, the three most important are: - Drill bits - Entry materials and - Backup materials.

In a preferred embodiment the present invention relates to extruded wood/polymer composite backup materials having a thickness of lmm to 3mm. The wood/polymer composite is recyclable and/or biodegradable. The novel backup boards of the invention are characterized in that they are homogeneous and may be prepared in a generally, continuous one-step process. The backup boards of the present invention also obviate many of the defects commonly related to drilling when the incorrect or inappropriate backup materials are used. These defects may be catergorised as: Nailheading, Smear, Gouging, and Burrs,

Selecting the appropriate backup material is fundamental to the drilling process in PCB fabrication. The purpose of the backup material is to prevent exit copper burrs on the underside of the drilled stack and to provide adequate space for drill stroke termination. The backup board also plays a role in the maintenance of the drill bit.

An acceptable backup material does not contain abrasives that would increase drill wear or introduce contaminants which may be evacuated through the drilled hole detracting from the integrity of the drill hole. The surface of a backup board should be smooth and hard to properly suppress exit burrs. The backup material should also have tight thickness and flatness tolerances to ensure drill hole quality. Some key specifications of a right backup material are: - Thickness tolerance less than +/- 0. lmm

- Dimension stability (flatness) - Hardness similar to the copper material used in the PCB, 80-90 shore "D" type - Suitable for sawing and drilling - Specific gravity 1.36- 1.42

There are a great variety of backup materials available. Selecting the appropriate "backer" requires extensive testing and qualification. Few of the products marketed and used as backup materials are engineered specifically for circuit board drilling. Typical materials include aluminum-clad wood

core composites, melamine-clad wood core composites, solid paper/phenolic boards, and even paper-resin hard board.

Specifications of the various backup materials available on the market:

The main problems with the existing backup materials are that they are: - Expensive to make, requiring 2-3 stage manufacturing processes, for example; impregnating phenolic or melamine paper, laminating aluminum sheet, hot pressing, coating etc. - Difficult and time consuming to make - Not suitable. Thickness tolerances for some materials are higher than the specifications required for small diameter drilling environmentally unfriendly, ie not biodegradable - non-recyclable or not practical to recycle.

As a consequence, the present invention is directed a novel process using inexpensive recyclable raw material to produce a more suitable backup material for the PCB industry.

Surprisingly the invention uses extrusion technology to prepare a plastic wood composite material comprising: (i) 10%-90 % natural fibres selected from paper, cardboard, rice, husk, bamboo, bagasse, semolina, straw, wood sawdust, wood flour and the like with moisture optimal 8%, max. 15%, particle size 100 - 500 micron. (ii) 0.01 %-50 % thermoplastic biopolymer or a natural starch such as maize, corn, rice, soya, cassava, yucca, or the like, and having a moisture content max. 14%, particle size 100-1400 micron and fat content 0.8- 1 %, and (iii) 0.01 %-90 % natural resins, plastic (polymer) and additives.

8. Example The use of wood waste and other cellulose based materials, as a raw ingredient for engineering wood products is not new. Mixed with resins and other binders and then compressed, these fillers have been used for decades in composite materials like particleboard and medium density fibreboard ( MDF) and other - primarily flat panel - products.

Surprisingly, by adapting technology first developed for the plastics and aluminum industries, engineered wood-based products are being extruded (as opposed to compressed) into just about any shape and dimension imaginable. Using a recipe of fillers, thermoplastic binders and other resins, components made up of 10- 90 % wood or cellulose are being custom extruded.

The preferred composites of the present invention contain (i) 70%-80 % natural fibres selected from paper, cardboard, rice, husk, bamboo, bagasse, semolina, straw, wood sawdust, wood flour and the like with moisture optimal 8%, max. 15%, particle size 100 - 500 micron. (ii) 10%-30 % thermoplastic biopolymer or a natural starch such as maize, corn, rice, soya, cassava, yucca, or the like, and having a moisture content max. 14%, particle size 100-1400 micron and fat content 0.8-1%, and (iii) 001%-10 % natural resins, plastic (polymer) and additives.

At the heart of this modified (for wood) extrusion technology is the recipe for the raw composite "mix" plus the die system that initially shapes the component. The beneficiaries of these new processes are the end users who can now extrude a myriad of components and finished products, including hollow parts, that out perform wood and in some applications, other engineered wood materials.

Wood composite process. The process may be split into 5 steps

- Material preparation- compounding - Extrusion- plasticizing in the extruder - Sizing- tooling - Calibration, cooling, - Cutting

Process steps

Before reaching the extrusion stage, there are multiple ways of treating and preparing the wood composite: the wood, biopolymers and additives may be compounded, agglomerated, or pelleted. The wood composite may even be directly extruded, although this will results in a loss of production capacity.

Turning now to the Flowchart labeled as Figure 3,

Step 1 pre-treatment. A cellulosic material containing a fine sawdust / natural fibre/ wood flour or other cellulose material such as paper, cardboard or carton material is first washed, filtered (screened), cleaned and dried.

Step 2 blending. The pre-treated material is then mixed with a natural starch such as maize and/or a natural resin in a blending operation to form a wood/biopolymer composite in the correct proportions (as given above) to form a metered and blended finished base composition suitable for compounding (step 3) or direct extrusion (step 4).

Step 3 compounding. The heat and pressure that is applied to the composition is such that the best results are obtained through the use of a twin conical (co- or counter rotating) extruder. This changes the physical characteristics of the raw material from a powder to a dough-like consistency. The dough-like composition can be stored for a limited period in dry airtight conditions for later use or is preferably, fed directly into the extruder in a continuous one-pot operation.

Step 4 extrusion. In the extruder, the following events take place. See Figure 1 - Plasticizing of the biopolymer (1) - Homogenization of wood/biopolymer composite (2) - Degassing (venting) (3) Compression and pressure build up at the right melt temperature (4).

A conventional extruder consisting of two slightly conical counter rotating screws placed inside of a heated barrel is preferred. At this stage material derived at step 3 is in a granule, pellet or step 2 powder form and is generally free flowing from the extruder hopper. The extruder hopper is placed on top of the extruder, and flows or is pulled under vacuum into the screw throat from where the screw will convey the material into the extruder. When accurate material feeding is necessary, external gravimetric feeders are used. Material moving through the extruder is melted mainly by means of the shear forces (friction) while it is conveyed through the length of the screw. At the end of the screw the molten material, or "melt" is fed in a solid continuous flow into through a tempered die attached to the extruder. The die is chosen to provide for the desired shape or thickness requirements. In the present invention the desired thickness may be anywhere between lmm and 3mm. A thickness of 1.5mm is the norm. The resulting extruded product is a homogeneous or plastic wood composite having a constant thickness and uniform dimensional stability. A thickness tolerance of +/- 0.1mm is easily achieved. Consequently the shape of extruded product is constant along its length. Degassing (venting). Due to water content in the composite, good venting is required. Before venting may be effected, the wood has to be integrated into the biopolymer to form a or plastic wood matrix. This prevents wood powder from being "sucked" through the venting system and consequent loss of valuable materials. The key function of the extruder is to produce highest quality melt, which is plasticized, homogenised, degassed and compressed at the correct melt temperature. Further, the or plastic wood composite has to remain free from distortion. Too long residence time in the screws or overheating due to unsuitable screws (uncontrollable excessive friction in the output zone) are the main reasons for wood defects.

Step 5. Sizing, tooling. The composition prepared is extruded through a high precision die to provide for thickness tolerances of +/- 0.1mm and a flat, dimensionally stable panel - and to provide for a pre-determined panel width.

Step 6. Calibration, Cooling. Optionally, the resultant extruded panel is then passed through a cold water calibration tank to bring the temperature of the panel down to room temperature.

Step 7. Cutting. The endless extruded panel is than passed through an online cut saw to cut to the desired length.

The process cycle is completed by collecting and recycling the panels made via steps 1-7 above once they have been used as backup boards in PCB manufacture. Once used, the old backup boards are collected, ground into a powder or granule and renter the process at the extrusion step, step 3.

The inventors have found that for plastic wood composites having the desired characteristics of the present invention, that conical twin screw extruders are preferred, although the invention is not limited these extruders alone. In general, conical machines have the advantage of minimal floor space requirements for a given output range. Robust gears with generously dimensioned thrust bearings (feasible on account of the diverging screw axes) make conical extruders ideal for high pressures as they are, for example, encountered in high-performance extrusion of profiles with small cross-sections. Conical twin-screw extruders offer a wider processing range and can cope with different output requirements and variations in the raw material properties better than parallel machines.

Figure 1 illustrates the flow dynamics of the blend prepared in step 2 as it moves through a counter- rotating conical twin extruder (100). The rotation speed of the screws (200) is 5-40rpm and the pressure gradient through the taper is from 100-350 bar. As depicted, the larger screw diameters occur in the feed section (1). The gradual increase compression forces along the screws' taper make conical machines very well suited for low density materials such as natural fibre formulations. The plasticising and homogenising of the integrated staring materials occurs about midway along the length of the taper and is indicated by zone (2). As previously discussed once plasticised the moisture and air released from the raw materials is vented (3) downstream of the plasticising zone.

Further, because of the screws' relative slimness in the metering section (4), shear stresses on the material is minimised. This is a particular advantage in the processing of natural fibre formulations keeping the fibre structure intact.

Figure 2 illustrates comparative residence times at various stages of product flow through the extruder. The top conical twin screws are compared with the lower parallel twin screws. The reader will instantly see that the metering section residence times under conditions of identical output favour the conical twin screw extruder where the melt passes the high-temperature zone twice as fast. This prevents darkening of fibre composites extruded at the necessary high mass temperature to plasticize the plastics material.

The correct screw geometry endeavours to take advantage of the reduced shear stresses necessary to prepare the melt and realize good melt quality, the ultimate goal of the extruder. The conical screw arrangement allows for compression and metering to take place at relatively low melt temperatures and pressures and for a relatively short residence time. Compression rate, volume, flight number, roller gap and flank gap, in each of the zones also has to be compiled into suitable screw geometry.

Where in the foregoing description reference has been made to integers or components having known equivalents then such equivalents are herein incorporated as if individually set forth.

9. Modifications Of The Preferred Embodiments

While the invention has been described with particular reference to certain embodiments thereof, it will be understood that various modifications can be made to the above-mentioned embodiment without departing from the spirit and scope of the present invention. The examples and the particular proportions set forth are intended to be illustrative only. For example, the precise combination of cellulosic materials used will vary depending on their availability, the time of year or due to seasonal fluctuations. The cellulosic material or mixture of cellulosic materials will however, be selected to ensure that the various parameters mentioned in the foregoing description will be complied with. The inventors have found that for plastic wood composites having the desired characteristics of the present invention, that conical twin screw extruders are preferred in the manufacture of these composites. The invention is not however limited to use of composites made using these extruders alone. Other extruders known in the art such as single screw extruders or conex extruders may also be used in building the composites.

Plastic wood composites having the desired characteristics of the present invention may also be used wherein the plastic component comprising the composite may also be varied depending on the desired drilling characteristics of the backup board. It will be understood though backup boards made using a higher proportion of thermoplastic polymer or other plastic polymer will be more expensive than those having a relative higher cellulosic content.

The skilled reader will also instantly realize that, although the Examples have been limited to the preparation of backup boards for use in the PCB industry the extruded or plastic composites may be fabricated for other uses particularly those requiring recyclable, biodegradable materials of a thickness of less than 5mm.

The reader will also be aware that the terms Backup board and Backer board are used interchangeably and refer to equivalent concepts.

Throughout the description and claims of this specification the word "comprise" and variations of the word, such as "comprises" and "comprising", are not intended to exclude other additives, components, integers or steps Preferred final product specifications:

Characteristic & applications: suitable for PCB drilling, Fabricating suitability: sawing or drilling, Thickness: 1.5mm standard (could produce from 1 mm - 3mm) Thickness Tolerance: +/- 0.1mm, Size: according to customer's requirement, Size Tolerance: +/- lmm Colour: grey /brown Specific gravity: 1.35 - 1.42, Surface Hardness: 83- 85, Biodegradable Recyclable

Appendix A.