PCB dry area summary of common problems (circuit line, solder mask, silkscreen)

1, BGA bit in the solder mask why the hole? What is the acceptance criteria?

A: The first solder stop plug hole is to protect the service life of the via hole, because the holes are generally required to plug the BGA bit aperture is relatively small, between 0.2--0.35mm, after the process of processing some of the holes within the hole is not easy Is dried or evaporated away, easy to leave a residue, if the solder does not plug the hole or the plug is not full, in the post-processing such as: spray tin, Shen Jin there will be residual foreign matter or tin beads, the customer installed When a component is heated at a high temperature, the foreign matter in the hole or the tin beads will flow out and adhere to the component, causing defects in the component performance, such as opening and short-circuiting. BGA hole in the solder resist hole A, must be stuffed full B, red or pseudo-not allowed to reveal the phenomenon of copper C, not allowed to have too much stuffed bumps higher than the side to be welded pads (will affect the components mounted Effect).

2, exposure machine table glass and ordinary glass What is the difference? Why is the exposure light reflector pit uneven?

A: The exposure machine table glass in the light through the light does not produce refraction. Exposure reflector flat if it is flat and smooth, then when the light shines on it according to the principle of light, it is formed by only one light reflection plate to be exposed to light, if it is uneven pit according to the light Principle, according to the light into the recesses and according to the projection of light will form numerous scattered light, the formation of irregular but uniform light to be exposed to the board, to improve the effect of exposure.

3, what is the side of the video? Side of the General Assembly caused by what kind of quality consequences?

A: Solder resist window unilateral green oil was developed out of the bottom part of the width of the area called side of the development. When the side of the development is too large also shows the developed out of contact with the substrate or the copper part of the larger green area, it forms the greater the degree of vacancy in the post-processing such as: tin spray, tin , Immersion gold and other side of the development of part of the high temperature, pressure and some aggressive attack on the green oil will be formed when the oil off, if there is a part of the IC bit off the green bridge, the customer welding components installed Will cause a bridge short circuit.

4, what is bad solder mask exposure? What kind of quality will it cause?

A: After soldering process exposed exposed in the process after the device mounting pads or soldered place, in the solder resist alignment / exposure process due to the light-blocking film or exposure to energy and operation problems, resulting This part of the covered green oil outside or all of the light to the occurrence of a cross-linking reaction, this part of the green oil in the development of the solution will not be dissolved, failed to expose the outer part of the pad to be welded or all, called the welding Poor exposure. Poor exposure leads to inability to mount components, poor soldering, and serious open leads.

5, lines, solder mask Why pre-treatment wear plate?

A: 1, the circuit board, including the foil board substrate and the hole after the pre-plated copper substrate. In order to ensure a firm adhesion between the dry film and the substrate surface, no oxide layer, oil stains, fingerprints and other contaminants are required on the surface of the substrate, no burr burr and no rough coating. In order to increase the contact area between the dry film and the substrate surface, it is also required that the substrate has a microscopically rough surface. In order to meet the above two requirements, the substrate should be carefully treated before filming. The treatment methods can be summarized as mechanical cleaning and chemical cleaning two categories.

2, the same solder mask is the same reason, solder mask before grinding plate is to remove some of the oxide layer of the board, oil, fingerprints and other dirt, in order to increase the contact area of solder mask and the board and more solid, It also requires a micro-roughened surface of the board (just like a car's tire, the tire must be roughened to better bond with the glue). If the line or before the solder mask does not take wear processing, to be film or to be printed on the surface of the solder mask has some oxidation, oil and the like, it will solder the line and the membrane directly separated from the board The formation of isolation, in the post-processing of the film here will fall off, peel.

6, what is the viscosity? Solder Mask ink viscosity of the PCB production What impact?

A: Viscosity - is a measure of stopping or resisting flow. Solder mask ink viscosity of PCB production has a considerable impact, when the viscosity is too high, easily lead to no oil or sticky network, when the viscosity is too low, the board will increase the mobility of ink, easy to cause oil into the hole And local oil book. Relatively speaking, when the thickness of the outer copper layer is thicker (≥1.5Z0), the viscosity of the ink should be controlled to be lower. If the viscosity is too high, the fluidity of the ink will be reduced. At the bottom of the circuit and the corner Will form oil, exposed line.

7, the development of net and poor exposure What are the same and different points?

A: The same point: a are in the solder resist after the exposed copper / gold soldered surface residual solder mask, b caused by the same reason, the drying time, temperature, exposure time, energy.

Different points: bad exposure formed by a larger area, residual solder mask oil are from outside to inside, and the width, Baidu are more uniform, most appear in the non-porous pads, mainly in this part of the ink has been UV Light exposure. The development of net residual solder mask is only a layer of oil at the bottom of the book, its small area, but the formation of a layer of membrane state, this part of the ink is mainly due to curing factors are not the same, with the surface layer of ink formation A hierarchical, generally appear in the hole pad.

8, why there is a bubble welding bubble generated? How to prevent?

A: (1), the solder mask oil is generally composed of the main agent of the ink + curing agent + diluent mixed together, the ink mixing in the air there will be some residual in the liquid, when the ink after scraper, silk After the webs are squeezed to the board, the gas inside the ink will evaporate rapidly and outwardly as the light or the equivalent temperature is encountered in a short period of time (2 ), The line spacing is too narrow lines too high, the screen printing ink can not be printed on the substrate solder mask, resulting in solder mask ink and the substrate there is air or moisture exists in the curing and exposure to heat generated by the expansion of gas bubbles, (3), a single line is mainly caused by the line is too high, the scraper and the line contact, the angle between the scraper and the line, so that the solder mask ink can not be printed at the bottom of the line, there is line between the side of the gas and solder mask ink , After heating will form a small bubble.

Prevention: a deployment of a good ink for a certain period of time before printing, b printed board is still a certain period of time so that the surface of the ink inside the ink slowly with the flow of the ink gradually evaporate, and then take a certain Bake at the temperature.

9, what is the resolution?

A: at 1mm distance, dry film resist lines or lines can form lines, the resolution can also be used to determine the absolute size of the line or space size, the dry film of the resolution and the resist film thickness and Polyester film thickness, the thicker the resist film layer, the lower the resolution, the light through the photographic plate and the polyester film knot dry film exposure, due to the polyester film scattering of light, the light side of the more Serious, the lower the resolution.

10, What is dry film and etching resistance and electroplating resistance?

A: Etch resistance: Photopolymerization of the dry film resist, should be able to resist ferric chloride etching solution, sulfuric acid by etching solution, acid chloride, copper etching solution, sulfuric acid - hydrogen peroxide etching etching solution. In the etching solution, when the temperature is 50 - 55 ℃, the dry film surface should be no hair, leakage, Qiqiao and off phenomenon. Electroplating: In acid bright copper plating, ordinary borosilicate lead fluoride, fluoroborate bright tin-plated lead alloy plating bath and the various plating solution, the dry film after polymerization resist surface hair should be no , Seepage, Qiao and off phenomenon.

11, Exposure machine exposure why vacuum?

A: Non-parallel light exposure operation ("point" as the light source of the exposure machine), the degree of vacuum absorption is a significant factor affecting the quality of exposure, the air is also a medium layer in the exposure if the board, film , There is air between the pumping film, then there will be refraction of light, affecting the effect of exposure, vacuum is not only to prevent the refraction of light, but also to prevent the gap between the film and the board will be expanded to ensure the right / The quality of the exposure.

12, pre-treatment using ash grinding plate What are the advantages? Disadvantages?

A: Advantages: a, abrasive pumice particles and nylon brush combined with the role of cloth and cotton tangency brush, to remove all the dirt, revealing fresh pure copper; b, to be able to form a completely grainy, rough, uniform , The surface of the multi-peak, there is no tillage groove; c, due to the role of nylon brush to ease the connection between the surface and the hole will not be damaged; d, due to the relatively soft nylon brush flexibility, can make up for Brush wear caused by uneven surface problems; e, due to the uniform surface without grooves, reducing the exposure time of light scattering, thus improving the imaging resolution. Disadvantages: the problem is that the pumice powder is easy to damage the mechanical parts of the equipment, the pumice powder particle size distribution control and the pumice powder residue removal on the substrate surface (especially in the hole).

13, the development point is too large or too small will have any effect?

A: The correct development time is determined by the point of development (the unexposed dry film is removed from the board) and the development point must be maintained at a constant percentage of the total length of the development section. If the development point is too close to the exit of the developing section, the unpolymerized resist film is not sufficiently cleaned and developed, and the residue of the resist may remain on the plate surface to cause a poor image development. If the development point is too close to the entrance of the development section, the polymerized dry film may become hairspray by Na2C03 due to the contact with the developer for a long time, causing the film to lose its luster and cause over-development. Usually the development point of control in the development of the total length of 40% - 60% (35% of our Division - 55%).

14, character printing before why bake plate?

A: Pre-baking characters before printing a plate is to enhance the binding force of the board and the character, b enhance the surface of the board solder mask ink hardness, to prevent character printing or post-processing process can easily lead to the resistance welding oil fork flower.

15, pretreatment wear plate mill brush Why swing?

A: there is a certain distance between the grinding wheel and the pin wheel. If you do not need to swing the grinding board directly, there will be many places that can not be worn, resulting in uneven cleaning of the board surface. There is no need to swing to form a straight groove in the board surface. Resulting in disconnection, without rocking hole easy to break holes and trailing phenomenon.

16, scraper to print what effect?

A: The blade angle directly control the amount of oil, scraping the blade edge uniformity directly affects the printing surface quality effects.

17, solder mask, the temperature and humidity in the darkroom circuit on PCB production have any effect?

A: When the darkroom temperature and humidity is too high or too low: 1, will increase the garbage in the air, 2, prone to sticky film phenomenon, 3, easily lead to film deformation, 4, easily lead to board oxidation.

18, why not use solder mask development point?

A "Since there are many variables that can be used in solder mask inks, the first is the variety of inks and the other intricate. The properties of each ink are different. The thickness of each ink in the plate is affected by pressure, velocity and viscosity during printing Are not the same, dry film is not as a single more uniform thickness, while the solder mask ink in the production process are also subject to different baking time, temperature, exposure energy, relatively speaking, The effect of the board are the same, so the actual solder resist development point is not meaningful.

19, how ghost is produced? How to prevent?

A: ghosting generally appear in white material board, and is generally in the position of the single-side window, because white material does not have UV light barrier function, PCB solder mask exposure, the unopened window will have some ultraviolet light Through the substrate to the edge of the PAD bit of the window, the green oil at the bottom of the green window is exposed and can not be fully developed and ghosted. Yellow ghost plate ghosting is usually due to the refraction or diffraction of UV caused by the general gold finger position is more common.

Prevention: 1, white plate window as much as possible on both sides of the design of such a large window. 2, in the case of single-sided window opening, the back of window opening is designed as large copper surface as possible. 3, when the window is single-sided and the back of the window opening for the substrate, the exposure of the substrate surface exposure energy than the window surface of the lower 1-2 cells.

20, solder mask on the PCB play a role?

A: solder mask ink: is a protective layer, coated with PCB in the PCB without welding the substrate and wiring. The purpose is to prevent bridging of wires during soldering while providing a permanent electrical environment and a chemically, thermally, and insulatingly protective layer while providing aesthetically pleasing appearance to the PCB. There are two major areas of solder mask ink: 1, thermosetting epoxy ink, 2, liquid photosensitive imaging ink.

21, solder mask over the cause of what is?

A: 1, the exposure energy is too low, 2, the development speed is too slow, the pressure is too large, syrup concentration is too high or too high temperature cylinder.

22, Solder Mask green board with a green bridge, why the green deck to face down?

A: Because of its relatively small width (minimum 0.08mm), the solder mask is relatively less resistant to developing potions and is sprayed from the nozzle onto the board when the green deck is down Only once the impact of the syrup, if the upward spray from the nozzle to the board on the syrup will bounce on the development of the upper cylinder will form a re-impact on the board, it will easily lead to broken green bridge, Therefore, the development of green solder bridge deck to face down.

23, what are the reasons for the green bubble?

A: There are: 1, pre-solder processing poor (too fast, the temperature is too low) resulting in the hole moisture is not fully dried, 2, poor hole plug hole gas, 3, Pre-character not pre-baking plate or after curing time is too long to cause green crisp, 5, after the process equipment temperature is too high.

24, testing conventional solder mask what are the items?

A: 1, hardness test (6H pencil), 2, acid, alkali, solvent (10%) at room temperature for 30 minutes, 3, adhesion (3M-600 # gluon), 4, Tin, 5, thermal shock (288 ℃ ± 5 ℃ 10 seconds ± 1 second) and so on.

25, Syria resisting diagonal shift screen printing machine and before and after, about shift screen printing machine in the production will have different effects?

A: Before and after the move around the screen printing machine and move around the screen printing machine in production, if the plate to be printed on the hole is a row of vertical or horizontal row, it is easy to cause green into the hole, while the shift is also easy to pollution About the edge of the plate, the printing process is very inconvenient to take the plate, and for the diagonal movement of the screen in terms of basic performance is superior to the first two, if the plate to be printed on the hole is a row of vertical or a Row sideways, oblique diagonal shift will not result in holes overlapped and lead to oil into the hole.

26, dry film Why do develop point?

A: By making the development point to adjust to get a more ideal development parameters speed. It would not be possible to determine the different development conditions for each dry film without developing the dots and it would not be known if the developer used would have the best developing ability under certain parameters. Usually developing point due to control at 40% - 60%.

27, why the maintenance of the developer with alkaline washing and pickling?

A: The first alkali wash is to play a role in cleaning, cleaning the residual dirt of each cylinder, green oil, pickling is to absorb and neutralize the cylinder wall, the nozzle residual alkaline substances and further cleaning.

28, how to improve the accuracy of solder alignment?

A: 1, to strengthen the practical skills of staff training, 2, 10 times with the mirror to check the accuracy of alignment, 3, control the service life of the film, 4, control the darkroom temperature in the required range Prevent film deformation, 4, in the four corners of the board design alignment accuracy mark.

29, pre-exposure plate Why pre-baking plate? And is low temperature (75 ± 5 ℃) baking?

A: The pre-exposure of the plate pre-bake: the ink is more volatile solvent out, but also to prevent the board when the ink has not been initial curing plate caused by sticky film, resulting in board out of oil and film pollution , Off the block. Solder Mask Liquid photosensitive ink curing temperature> 85 ℃ curing easily die, while in the process of printing due to its viscosity and fluidity, so some pads and SMT parts of the substrate and some of the hole ink It will be thinner. If it is baked at a temperature higher than 80 ° C, it will be completely cured, and when it is irradiated with high-energy ultraviolet light at the time of alignment exposure, the ink in this part will be completely cross-linked. At the time of developing It is not easy to be dissolved by sodium carbonate solution, resulting in the development of net.

30, how to improve the solder mask on the plate after exposure of the film negatives appear?

A: 1, in the right before the extension of the plate pre-drying time (can not increase the temperature), 2, appropriately reduce the exposure machine (10-15%) of the vacuum, 3, reduce the exposure energy, 4, control Filming surface cleaning quality and service life. 5, control the frequency of friction should not be too much.

31, what is the network distance?

A: According to the principle of printing, when the printing is carried out in the close contact state, the screen will not be extended and the dimensional accuracy of the printing can be obtained. However, in fact, the oil film is easily infiltrated and the printing can not be performed very cleanly The most basic requirement is the screen to be printed on the board surface with a certain gap, which is the so-called network distance. (General network distance control in 3-5mm)

32, what is the Internet?

A: The purpose of this paper is to express the numerical value of the hole density of the screen, which is expressed by the number of 1-square-inch mesh. Nowadays, the number of holes per square meter is more than that of Western Europe, West Germany, Switzerland and Italy, Mesh is the number of units, while Japan is based on inches. Usually "head" is also called "T".

33, the line Why do indentation test? And must be ≥ 4mm?

A: The lines do indentation is to detect the film machine when the pressure roller up and down parallel to the level of parallelism, and according to the actual situation of the indentation test, to adjust the pressure reel to get the best filming ability. The indentation test must be ≥4mm, because under normal circumstances the pressure roller and the pressure roller under the pressure in the film when the two pressure rollers are respectively in contact with the plate area = 4mm, if <4mm then two pressure reel and the plate surface Dry film contact area is also less, the force applied to the dry film will be reduced and ineffective, it will result in bad film, dry film and the combination of the surface is not good.

34, what is the maximum and minimum optical density of film?

A: The optical density, the maximum optical density required Dmin (minimum)> 4.0, the minimum optical density Dmax <0.17 The maximum optical density refers to the bottom plate in ultraviolet light, the light blocking film on the surface of the lower limit of light block, when the bottom plate opaque The area of the light density Dmin is equal to 4.0, the light transmittance of 0.03%, so Dmin exceeds 4.0 in order to achieve a good light blocking purposes. The minimum optical density refers to the bottom plate in the ultraviolet light, the light blocking film outside the transparent film presented by the upper limit of light-blocking, when the bottom plate opaque zone Dmax = 0.17, the light transmittance of about 70%, so Dmax (maximum ) Is less than 0.17, in order to achieve good light transmission purposes.

35, the line what causes plating will occur when plating?

A: 1, poor performance of dry film, over the use of the validity; 2, the substrate surface is not clean or rough surface of the poor, poor adhesion of dry film; 3, film temperature is low, fast delivery, , The exposure energy is too high lead to brittle corrosion resistance; 5, the lack of exposure to develop the slow speed of the film caused by the hairline hair curling resistance; 6, plating liquid temperature before treatment is too high.

36 liquid photosensitive ink light imaging principle is what?

A: When the photosensitive ink is exposed to ultraviolet light, the photoinitiator breaks down into free radicals to attack the resin to form a free-radical polymerization and instantly increase the size of the polymer molecules. In this case, the ink should be insoluble in 1% sodium carbonate, but soluble in strong Alkali 5-10% sodium hydroxide, so as to achieve the purpose of being able to develop but also to save the problem board in time, the printed board pad part is blocked by the film stop point of the unexposed ink when removed, the exposed part of the developed After reservation.

37, dry film development is not net, there are more than one reason for what glue?

A: 1, the dry film of poor quality, such as large or high molecular weight, in the process of using dry 4 occasional thermal polymerization, etc .; 2, dry film exposure to white light caused by partial polymerization; 3, exposure time is too long or too energy High; 4, the production of film stop light spot the most optical density is not enough, resulting in ultraviolet light caused by partial polymerization; 5, the developer temperature is too low or too low concentration, the development speed too fast, the pressure is too small; In a large number of bubbles to reduce the ability to develop.

38, exposure machine which factors will have an impact on the PCB?

A: The frame, light source, temperature control system, exposure control system, vacuum system

39 general pretreatment Why wear marks test?

A: Pre-treatment machine wear mark is to detect the balance of brushing, evenness, but also through the wear-scar test to get the different thickness of the grinding plate current parameters.

40, the developing cylinder nozzle why the fan-shaped? Why is not the cone?

A: Because there is a certain distance between the nozzle and the nozzle of the developer developing cylinder, it is fan-shaped, then the area that can be wetted by the syrup sprayed out is sure to be relatively wide and even, and at the same time, it also compares the spray in the hole Even, if it is conical spray it syrup in the same process conditions, relative to the fan-shaped nozzles, its uniformity is poor.

41, why the increase in the development of automatic increase developer cylinder? Why do not wear plate machine?

A: The first mill plate grinding machine pickling (sulfuric acid) only to remove part of the oxide, the most important is to add the role of grinding brush, when the board after the acid tank spray, the board away from the acid tank Acid solution is only a small part of the original concentration of less than its impact (3-5%), the general oxide 3-5% of the acid can be dissolved off, the developer of the developer is (sodium carbonate) When it is dissolved in water is not a 100% complete aqueous solution, it still forms some finely grained particles which are carried out of the developing cylinder by the plate as part of the sodium carbonate solution is being dissolved during development.

42, the development of the developer pout will automatically swing and will not automatically swing What is the difference between the effect?

A: It will automatically swing it on the board spray will be more uniform, especially the fine lines, a swing can better solve the problem of net and residual film development, and can enhance the dissolution of the remaining film hole, Improve the developing ability.

43, after the solder mask printing line bubbles on the surface and the substrate surface bubbles, both for the same reason? why?

A: Line bubbles at the edge of the line are: ① line conductor is too high or side eclipse relatively large, ② printed board pre-bake silent parking time is too short, ③ ink viscosity is too high or too much solvent water in the ink, ④ ink printing layer thickness is too thick, ⑤ uneven deployment of ink or deployment of good ink static time is not enough.

Substrate surface bubbles are: ① uneven deployment of ink or deployment of a good ink is not enough parking time, ② board surface moisture or dirt, ③ ink viscosity is too high or the printing layer is too thick, ④ oven temperature uneven and so on.

44, grinding plate drying section set Why is the strong wind dry, hot air dry, cold dry, their order can be reversed?

A: Can not be reversed, because the other hand, the cold dry in the first paragraph simply does not play much role, when the strong wind drying in the first paragraph, the water blown out from the hole after a strong wind blowing, plus High temperature blowing, drying easily volatile, there will be no traces of water left on the board, if the hot air drying in the last paragraph, the board into the darkroom surface temperature is relatively high (60-80 ℃), while the darkroom The temperature is generally between 18-24 ℃, then the board is easy to produce oxidation.

45, solder mask printing machine why there should be this shift?

A: 1, to avoid the ink on the plate (the same hole) due to repeated scraping scraper twice and into the hole, but also can increase the uniformity of ink coating.

46, the development of the developing tank liquid chemical Why defoamer?

A: Because the developing tank within the developing solution with the use of time increases and the amount of plate increases, the solution will gradually reduce the in-cylinder residual ink, the more accumulated, with the long solution of repeated spray to use There will be impurities and foam, if too much foam left on the board, over the washing machine washing section is difficult to wash away, will cause defects in the appearance of the board, and add defoamer is to dissolve the foam inside the developing cylinder .

47, the viscosity of carbon oil on the quality of PCB have any effect?

A: The viscosity of carbon oil directly affects the resistance of carbon oil

48, affecting the quality of the screen printing What are the factors?

A: 1, the nature of the ink: ink viscosity, fineness and liquidity; 2, the screen state: mesh choice of use, tension and photosensitive plastic coating; 3, screen printing conditions: printing pressure, scraper hardness, Angle and printing speed; 4, human factors: operator skill and quality of consciousness; 5, environmental factors: indoor temperature, temperature, degree of purification and so on.

49, what is dry film speed?

A: The dry film speed of light refers to the photoresist in the ultraviolet light irradiation, the photopolymerization of monomers to form a polymerization reaction with a certain degree of corrosion resistance of the polymer and the amount of light energy. In the case of light intensity and light fixed, the speed of light performance for the length of exposure time, the exposure time is light sensitive speed.

50, what is the dry film exposure time tolerance?

A: After a dry film has been exposed for some time, the photoresist layer has been fully or mostly polymerized by development. Generally, the resulting pattern can be used, which is called the minimum exposure time. The exposure time to continue lengthening, the photoresist polymerization reasoning thoroughly, and after the development of the graphics size is still consistent with the film size, the time is called the maximum exposure time. In general, the optimum exposure time for dry film is chosen between the minimum and maximum exposure times. The ratio of the maximum exposure time to the minimum exposure time is called exposure time latitude.

51, solder mask ink is too thick or have any impact on the book?

A: When the solder mask ink is too thick (higher than the chip or the IC bit), the post-processing process can cause the solder paste due to bad or poor soldering, it can also cause the components to be attached to the bad or even to be mounted. The ink Overbooking will result in insulation is not thick enough circuit, it will have leakage phenomenon, affecting the performance of the product after the process.

52, conventional solder mask ink too thick or have any effect?

A: Because the solder mask ink is not only a protective layer, but also an insulating layer, if the book, then the voltage is too large or a certain environmental impact, the line is prone to leakage phenomenon, when the two lines spacing is small To a certain extent, the arc will be generated between the two lines, if the line insulation book over the book will easily be punctured, resulting in short circuit. When solder mask printing, the corner of the circuit is more difficult to print the oil, if the corner when the ink is thick enough, other places, such as large copper surface ink thickness is even thicker.

53, solder paste hole ink Why use source solution without adding oil and water?

A: Because the source liquid plug hole is relatively speaking, it contains less water, the high viscosity plug will not flow after the plug will result in not full, in the post-curing with the liquid water volatile it Shrinkage is relatively small, at the same time it will not post-curing because of the high temperature caused by the body's water to form a sudden outward volatilization or cracking phenomenon, if you add oil-water it's lower viscosity, ink Liquidity is relatively strong, when the plug is easy to flow will cause the plug hole is not full and poor solder mask surface, the liquid in the post-curing of the liquid ink will be volatile and lead to plug the hole oil or poor plug.

54, what is dry film developability and developability?

A: Dry film development refers to the best working condition of the dry film film, the image obtained after exposure and development of good or bad, that is, the circuit image is clear, unexposed parts should be removed without residue, after exposure to remain The surface of the resist (dry film) should be smooth and solid without edge. Dry film development resistance refers to the degree of exposure to dry film over-development, resistance to development reflects the tolerance of the development process.