Silk screen printing, carbon ink, silver glue, strippable glue and copper paste process terminology manual

1. Angle of Attack
Refers to the forward-inclined three-dimensional angle formed by the moving scraper surface and the plane of the screen during screen printing.

2. Bias
Refers to a special screen stretching method for screen printing, that is, abandoning the orthodox stretching method in which the warp and weft directions of the screen are parallel to the outer frame, and deliberately making the warp direction of the screen and the longitudinal direction of the screen frames on both sides form a 22° combination. As for the screen of the graphic film, it is still pasted in the direction of the screen frame. In this way, when the scraper pushes the ink forward, it will generate a lateral driving force. For example, when printing green paint, it can make it have a more sufficient ink distribution behind the board surface line. However, this "oblique screen stretching" method is very wasteful of screen cloth. Generally, it is still possible to use the straight screen stretching method and change to the oblique film sticking method, or print once each way back and forth, which can also solve the problem of missing printing. Bias also refers to the weaving method in which the warp and weft yarns of the screen cloth are not vertical.

3. Bleach
In the preparation process for screen printing, in order to make the mesh on the recycled screen have better adhesion with the stencil or photosensitive emulsion, the used mesh must be brushed, cleaned and roughened with bleach or fine diamond sand as a detergent for recycling.

4. Bleeding
In the circuit board manufacturing process, it often refers to the possibility that there are still holes after the through-hole copper wall is completed, so that residual liquid often flows out. Sometimes it also refers to the printed liquid resist pattern, which may have a small amount of components overflowing from its edge during the subsequent drying process. For example, traditional baking green paint often has this problem.

5. Blockout
After the indirect screen is completed and the stencil is attached, the empty mesh on the periphery must be filled and sealed with hydrosol to avoid ink leakage at the edge during actual printing.

6. Blotting Dry printing
After the "screen" has been scraped and printed several times, there is often excess ink on the downward printing surface. White newspaper must be used instead of the circuit board. Without covering the ink, a scraper (called a scraper in the mainland industry) is used to dry print once to absorb the residual ink on the edge of the pattern. This is called Blotting. Traditional baking green paint must be dry printed continuously to maintain the quality of the edge of the green paint printed on the circuit board.

7. Blotting Paper Water-absorbing paper
Paper used to absorb excess liquid.

8. Calendered Fabric Calendered Fabric
is for traditional PET mesh (trade name Tetoron), nylon mesh and stainless mesh, etc., the scraper surface is specially flattened on one side to make it easier to scrape ink and make the "printing ink" thinner, so that the exposure of UV ink is easier and more thorough. It is said that the size of these meshes is more stable and the ink thickness is more uniform, but some practical reports are not entirely true. Moreover, this "rolling flat process" is not easy to carry out, and often the rolling thickness is uneven, and even wrinkles are generated. Currently, UV inks have been quite advanced, so this type of rolled flat mesh has gradually disappeared.

9. Carlson Pin
It is a stainless steel positioning pin with a flat, thin and wide base (1.5"×0.75") and a short stake. When the plate to be printed is in the printing construction, its base can be pasted to a fixed position on the printing table with a thin tape, and then the tool hole of the plate to be printed is inserted into the short pin to facilitate the alignment of the screen pattern. The short pin is spot welded to a corner of the rectangular base surface. Usually, the diameter of the short pin is 0.125" and the height is 0.060".

10. Chase screen frame
When screen printing is used as a tool for image transfer, the square outer frame that supports the screen cloth and the film pattern is called a screen frame. The current screen frame is mostly welded with hollow or solid aluminum bars, also known as Frame.

11. Copper paste
It is a paste made by mixing copper powder and organic carrier, which can be used to print simple circuit conductors on the board.

12. Cure
In the monomer state, the polymer will absorb heat or light energy with the help of catalyst and undergo chemical reaction, gradually changing its original properties. This phenomenon of cross-linking into polymer is called Cure. Curing Agents also refer to hardeners.

13. Direct Emulsion
It is a photosensitive emulsion resist used on single-panel printing mesh. It can directly seal the mesh and is more durable than the indirect stencil attached to the mesh. However, the "realistic straightness" Definition of the pattern edge is not good, so it can only be used for single-panel image transfer with thicker lines.

14. Direct/Indirect Stencil
It is a method of attaching an indirect stencil to the mesh. Because the film layer is very thick, and after being sprayed with water, the capillary action will occur, causing the film to expand and squeeze into the mesh, so it also has the advantages of direct latex, such as Ulano's CD-5.

15. Durometer
It uses a spring-loaded metal probe (Indentor) to press on softer rubber or plastic to measure its hardness. For example, the common Durometer "A", that is, after 1 kg of gravity is pressed down for 1 second, the degree seen on the surface is the representation of this hardness. The PU scraper required for screen printing has a hardness of about 60 to 80 degrees, and this durometer is also required to measure it.

16. Fabric
Refers to the carrier "mesh" on which the printing screen is stretched on the screen frame. Usually, its materials include polyester (PET), stainless steel and nylon, etc. This term is also called Cloth.

17. Flood stroke Print
It means that before the actual printing of the pattern, the ink is evenly applied on the mesh with a flood bar, and then the scraper is used to scrape the print. This method is very useful for thixotropic inks.

18. Ghost Image
In screen printing, the edge of the printed image may be unclean due to the uncleanness of the edge of the mesh or the plate film, which is called Ghost Image. Hardner (or Curing Agent) - refers to thermosetting coatings containing epoxy resins (such as green paint, text white paint, liquid photosensitive green paint, etc.), which have two components packaged in two liquids, one of which is the hardener. Once the two liquids are mixed and applied, the cross-linking function of this hardener will cause the liquid paint to harden or harden (hardening) at high temperature, that is, polymerization (Polynorization) or cross-linking (Crossinkage) reaction occurs, becoming an irreversible high molecular polymer. This hardener has other names, such as bridging agent, cross-linking agent, etc.

19. Legend word mark, symbol
Refers to the text symbols or numbers printed on the surface of the finished circuit board, which are used to indicate the location of various parts for assembly or replacement. Usually, the arrangement of various parts (such as R for resistors, C for capacitors, U for integrated circuits, etc.) is from the upper left corner of the front of the board, first to the right and then to the bottom, and the codes and numbers are assigned in order according to the order of the parts. This kind of text printing is mostly done with permanent epoxy resin white paint, and a few are also printed with yellow paint. When printing, be careful not to contaminate the solder pad to avoid affecting its solderability.

20. Mask Resistors
Refers to the entire board entering a certain process environment to perform a certain treatment, and if the local board surface does not want to be treated, it must be covered with some kind of protection to isolate it from the environment and not be affected by it. This kind of masking film is called "Mask Resistors", such as "Solder Mask Solder Resistors".

21. Marking Marking
refers to the material number (P/N), revision letter, manufacturer's logo and other words and symbols printed on the board with white epoxy resin paint. It can be used interchangeably with Legend, but it is not exactly the same.

22. Mechanical Stretcher Mechanical Stretcher
A machine that stretches the mesh to the required tension. The mesh can be fixed on the screen frame to form a screen carrier for printing only after it is straightened and flattened. In the early days, the mesh was stretched in all directions using a mechanical rod-type output tool. Now it has been changed to a pneumatic tensioner, which makes the tension more uniform and the stretching action more gentle to reduce the rupture of the mesh.

23. Mesh Count
This refers to the number of warp and weft threads of the mesh and its weaving density, that is, the number of threads per unit length, or the number of openings. It is an important parameter for screen printing. The higher the mesh number, the smaller the opening, and the better the edge resolution of the printed graphics. Since this type of stainless steel or polyester mesh is mostly produced in countries that use the metric system, such as Japan and Switzerland, its number is determined by the number of threads per cm. For example, a 55T mesh for printing green paint can be converted into 140T per inch in the British system; a 120T for printing lines can be converted into 305T. The metric system is more accurate. The letters following the various mesh numbers are used to express the fineness of the mesh. There were originally three types: S (Small), T (Thick) and HD (Heavy Duty). Currently, because S is rarely used, only the latter two types are left in the product.

24. Metallized Fabric Metallized fabric
It is a polyester mesh with a chemical nickel layer on its surface, which makes the mesh stronger and more stable, and makes the ink leakage of the mesh opening smoother, making the performance close to that of stainless steel mesh, but the price is much cheaper. However, the elasticity of this "metallized fabric" is not very good, the opening will become smaller, and the nickel layer will crack when used. In Taiwan's high-humidity marine climate, it is easy to rust, so it has not been used in China.

25. Monofilament
It refers to the shape of the silk thread in the mesh used for screen printing. At present, almost all kinds of mesh have completely adopted monofilament. In the early days, twisted multifilament was used, but it was gradually eliminated because the mesh opening, resolution and control of characteristics were far inferior to monofilament mesh. The current stainless steel or synthetic silk materials have improved a lot in all aspects compared with the early days.

26. Negative Stencil Negative photosensitive film
Refers to a photoresist film that can produce a polymerization hardening reaction after being exposed to light. This word Stencil is a photosensitive film that can be attached to a stretched mesh to transfer images in a screen printing manner and complete an indirect printing screen. Almost all graphic printing (Graphic Printing) used in various fields uses this relatively cheap photosensitive chemical as a tool for images.

27. Newton (N) Newton
When an object with a mass of 1 kg is subjected to an external force that generates an acceleration of 1 meter per second per second (1 m/s2), the magnitude of the external force is 1 "Newton", abbreviated as 1 N. In the preparation work for screen printing, the unit tension that needs to be reached by stretching the screen (the mainland term is stretching the screen, which seems to be more appropriate) can be expressed as a number of N/cm2 (1 N/cm2=129 g/cm2).

28. Nomencleature
: It refers to the white characters and symbols printed on the green paint surface for the convenience of downstream assembly or maintenance. The purpose is to indicate the parts to be installed to avoid errors. There are other terms for this kind of "nomencleature", such as Legend, letter, and Marking. In the early days, there were other colors such as yellow and black, but now they are almost all white epoxy resin inks.

29. Nylon:
It was translated as "nylon" in the early days. It is a kind of Polyamides. It is a thermoplastic resin. In a wide temperature range (0~150℃), its tensile strength and flexural strength have quite good results, and its electrical resistance, acid and alkali resistance and solvent resistance are also very good. In the electronics industry, it is mostly used for the outer insulation layer and filler of enameled wires, and in the circuit board industry, it is used on the mesh material of screen printing.

30. Off-Contact Overhead
In the combination of screen printing, the ink surface of the screen cloth is still a certain distance from the copper surface of the board when there is no construction operation (Off-Contact-Distance, OCD, usually 0.125 inches). Only when the right-angle blade line of the scraper is pressed down, the screen cloth will show a V-shaped partial contact on the copper surface. This situation where it is not completely flat is called Off-Contact. In addition, during the fully automatic dry film image transfer, the parallel light exposure station in the clean room also presents this non-contact "overhead" between the glass film and the circuit board surface to facilitate the free transportation and advancement of the board. This overhead exposure method is the highest level of photosensitive image transfer.

31. On-Contact Printing
Refers to the printing method in which the printing plate is completely flat on the surface of the printed material, and then the ink is pushed by a scraper, such as the stencil printing method of solder paste. After printing, the whole frame can be lifted off the printing surface, leaving solder paste on the circuit board. Different from this is the off-contact printing method, which uses the tension of the stretched screen. When the scraper moves forward and presses down to print, the mesh behind the scraper also bounces up at the same time, so that the printed pattern can remain clear. Common screen printing methods belong to this category. Now let's use a simple diagram of solder paste printing to explain the difference between the two.

32. Plain Weave
It refers to a weaving method of the mesh used in screen printing, that is, when the warp and weft yarns are woven in a one-over-one-under manner, it is called "plain weave". As far as screen printing is concerned, plain weave mesh has the best ink leakage. The popular meshes today are all made of monofilaments, so when the mesh count continues to increase and density reaches a certain limit, the wire diameter is too fine, resulting in insufficient strength and it is impossible to weave the mesh required by printing. Usually, when synthetic fibers (mainly polyester "Tetoron") reach more than 300 mesh/inch (120 mesh/cm), they cannot be used due to insufficient tension. Stainless steel can be denser to 415 mesh/inch (or 165 mesh/cm) and still maintain sufficient tension. At present, the plain weave mesh used in "screen printing" only uses monofilaments to facilitate cleaning, regeneration and weaving. However, the multi-filament flat weave method is still used for the weaving of glass fiber cloth in the sheet film (Pupreg) in order to improve its dimensional stability and facilitate the impregnation and penetration of resin, and to increase the contact area and adhesion.

33. Plug pin, plug pin
In circuit boards, it often refers to the male pin part of the connector or socket, which can be inserted into the hole for interconnection and can be withdrawn at any time. The word "plugging" sometimes refers to "plugging the hole", which is a special resist that protects the hole wall so that the outer layer board can be positively etched. Its purpose is the same as the capping method. However, the plugging method can achieve the point of no ring (Landless) on the outer layer to increase the density of wiring.

34. Pneumatic Stretcher
It is a stretching tool for screen making. It can clamp the screen from four sides with its clamps and stretch it carefully, slowly and evenly in a "pneumatic" way. It can also set and change the required tension. After it reaches the required data, it is fixed on the screen frame with glue to become a carrier for circuit patterns and scraping ink. Because the tension can be controlled by air pressure, it is more accurate than the tension of "mechanical" stretching, which helps to implement precision printing. The left picture shows the quick clamp and pneumatic pump of the "pneumatic stretcher". The right picture shows a lifting screen stretching platform with multiple stretchers.

35. Poise It
is a unit of "viscosity", equal to 1 dyne. sec/cm2, and the commonly used unit is Centipoise (abbreviated as Cp). The viscosity of commonly used solder paste is between 600,000 Cp and 1 million Cp.

36. Pot Life
refers to the two-component glue or coating (such as green paint). When the main agent and its special solvent or catalyst (or hardener) are evenly mixed in the container, it becomes a construction material. However, once mixed, the chemical reaction begins, and it will not be usable until it is almost hardened. The period of time that it can be used in the container is called Pot Life or Working Life.

37. Reclaiming refers to
the indirect screen printing process. When the original stencil on the mesh needs to be removed and a new stencil is to be applied, the original stencil should be softened with chemicals first, then rinsed with warm water, or the mesh should be further roughened so that the new stencil can be attached firmly. These processes are called Reclaiming.

38. In addition, this word also refers to the recycling of certain wastes. Relaxation
is an abnormal phenomenon that occurs during the screen stretching process. When the "net clamp" pulls the mesh cloth outward suddenly, the mesh cloth will temporarily feel loose and weak. After a period of reaction, the mesh cloth gradually shows the strength of tension. This is because the physical property of the mesh material itself has the phenomenon of "cold flow" and the process of redistribution of potential energy on the entire mesh cloth. The correct "net stretching" steps should be adopted for on-site operations. Before the next tightening, it is necessary to relax a little, and then pull to a greater tension to reduce the occurrence of the above-mentioned "relaxation".

39. Resistor Paste The
carbon powder with uniform particle size is mixed into a paste, which can be used as a 20-50Ω/sq printed resistor (Resistor). This printed "resistor" must meet the requirements of uniform thickness and neat edges. However, unless the use environment of simple resistors is particularly good, generally after a period of use in a warm and humid environment, its performance will gradually deteriorate.

40. Roadmap: Layout of circuits and parts
Refers to the use of non-conductive coatings to print the layout of circuits and parts on the board surface to facilitate service and repair work.

41. Screen Printing: Screen printing
It is to use a scraper to squeeze out an appropriate amount of ink (i.e., resist) on the mesh with a negative pattern, and form a positive pattern through the partial mesh, which is printed on the flat copper surface of the substrate to form a covering resist, preparing for subsequent selective etching or electroplating. This transfer method is generally called "screen printing", and the mainland industry calls it "screen printing". The screen materials (Screen) used include: polyester (Polyester), stainless steel, nylon and obsolete silk fabrics (Silk) and so on. Screen printing can also be used in other fields.

42. Screenability: Screen printing ability
It refers to the ink in the screen printing construction, under the action of scraping and pressing, through the exposed part of the mesh, and smoothly leaks onto the board or copper surface, and has good adhesion. When the obtained ink pattern also has good resolution, it can be said that the board surface, ink, or the machine used has good "screen printing ability".

43. Silk Screen Screen Printing, Silk Screen Printing
Using polyester mesh or stainless steel mesh as a carrier, the pattern of positive and negative films can be transferred to the mesh of the screen frame by direct latex or indirect film method to form a screen, which is used as a tool for printing on the surface of the flat plate. It is called "screen printing" method. The mainland term is abbreviated as "silk screen printing".

44. Silver Migration It
refers to the long-term aging process between conductors such as silver paste jumpers or silver paste through holes (STH) in a high humidity environment. When there is a DC bias (Bias, which means that the potential of the two conductors is not equal), there will be several mils of silver ion crystals between each other, causing the deterioration of isolation quality (Isolation) or even leakage, which is called "silver migration".

45. Silver Paste
Refers to a polymer paste made of 70% by weight of tiny silver flakes and 30% of resin, with a small amount of high-boiling-point solvent added as a thinning agent to facilitate screen printing. Generally, the additional jumpers or through-holes added to the board can use silver paste instead of the orthodox PTH, which is specifically called STH (Silver Through Hole). This method has the advantages of simple equipment, fast construction, no waste water trouble, and good conduction quality. Its resistance value is only 40mΩ/sq. Generally The cost of STH is less than two-thirds of that of PTH. It is the favorite of low-power simple function circuit boards and is often used in various electronic devices such as remote controls or desktop telephones. The global production of STH boards is mostly concentrated in Southeast Asia and South Korea, and the silver paste used is mainly Japanese products, such as Fujikura, Hokuriku and other brands. In recent years, most board jumpers have been changed to carbon glue, and silver paste is specifically used in the field of through-hole double-sided boards. It is not easy to achieve customer acceptance of the "silver through-hole" technology, and problems such as breakage, looseness, and "migration" often occur. There are not many reference documents available, and we can only rely on our own luck and experience to overcome difficulties on site.

46. Skip Printing, Skip Plating
During the printing process, some dead corners of the board may cause missing prints due to poor ink distribution, which is called Skipping. This phenomenon is most likely to occur during the conformal coating or green paint printing process, because the corners on the back of the three-dimensional circuit often cannot get enough green paint due to uneven force or insufficient ink, thus forming "skipping". As for skipping plating, it refers to the strong turbulence of the tank liquid or the low current area during electroplating, such as near the hole mouth and the central part of the hole wall of the small hole, or due to the obstruction of bubbles, resulting in poor distribution of the plating layer, which gradually makes it difficult for the plating layer to grow. See also Step Plating.

47. Snap-off rebound height
Refers to the height of the screen cloth from the board surface during screen printing; that is, the depth of the scraper pressing down to the board surface. Another way of saying it is "off-contact distance".

48. Squeege scraper
Refers to the tool that pushes the ink on the screen in screen printing. The main material of the scraper is PU (Polyurethane), and the pressure of the right-angle blade can be used to squeeze the ink through the opening of the mesh and reach the printed board to complete the transfer of the pattern.

49. Stencil film The
indirect screen, one of the important tools of screen printing, has a layer of pattern attached to the "ink printing surface" of the mesh, which is the "film". This kind of stencil also uses a special photosensitive film, which can be transferred from the film, exposed, and attached to the mesh after development, and then baked and the protective film is torn off to become a screen.

50. Tensiomenter tension meter
When the mesh on the screen frame has been stretched and fixed, the "tension meter" can be used to measure the tension of the mesh. The unit is more commonly used in Newtown/cm. The principle of this measurement is that there are two fixed support rods on both sides of the base, and there is another shorter, freely sinking active support rod in the middle. Under the gravity of the counterweight, this "active short rod" will "fall" on the mesh to be measured, so the "tension" supported by the local mesh can be measured. The calibration method is to first place the "tension meter" upright on a flat glass plate, and adjust the surface reading to zero with a hexagonal screw below, and then it can be used to measure the tension of the mesh. (This article is guided by Mr. Yang Zhixiong of Fansheng Company, and I would like to thank him.)

51. Thinner Thinner
is the "solvent" used for dilution. Generally speaking, the thinner must not react chemically with the solute to be diluted.

52. Thixotropy, thixotropy, thixotropy, static coagulation
Certain colloidal substances, if stirred, shaken, or vibrated, will liquefy and flow, but when they are completely still, they will stick and solidify. This characteristic is called thixotropy. Common examples include ketchup or clay mud. Ink used in printing in the circuit board industry, especially green paint or solder paste, must have this "anti-sag" property to prevent the printed three-dimensional "ink" or "paste block" from collapsing or flowing.

53. Ultra Violet Curing (UV Curing) Ultraviolet curing Ultraviolet
light refers to electromagnetic waves with a wavelength of 200 to 400nm (nm refers to nanometer, i.e. 10-9m; it can also be written as mμ, mili-micron), which is beyond human vision. The light waves in this field have strong energy. The most sensitive wavelength of the photosensitive coating material used for plate making is about 260 ~ 410nm. Its specific energy can be used to quickly harden the photosensitive coating without baking and diluent, which is very beneficial to automation. The circuit board industry can use UV curing ink for circuit printing, which is widely used in direct etching of single-sided boards or inner-layer boards.

54. Twill Weave, Diamond Weave
It is a twill weave of mesh cloth. The common plain weave (Plain Weave) is a kind of twill weave of the cloth. The warp and weft yarns in the cloth are interwoven up and down. Twill weave is a jump weave method such as one up and two down, or two up and two down. It looks like twill cloth from a large area. How this kind of mesh cloth works on board printing has not been seen in various documents.

55. Viscosity
In the circuit board manufacturing process, this term simply refers to the resistance (resistance) that occurs when the ink flows (flow) under external thrust, which is called viscosity. Generally, thinner inks have lower viscosity, while thicker inks have higher viscosity. As for the true definition of viscosity, it is related to the properties of various fluids, and its calculation is quite complicated (see the special article in the 47th issue of Circuit Board Information Magazine for details). CCL Copper Clad Laminates; Copper foil substrates (called "copper clad laminates" by mainland companies)