7. Documentation and process review.
The technologist or foreman of the screen printing process should focus on the technical aspects as follows:
(1) Establish a detailed work specification for the whole process of the silk screen process, specify the process parameters of each process, establish the corresponding process review report, and maintain the equipment.
(2) Check the temperature and humidity of each room in the screen printing every day and record it.
(3) Check the status and operating parameters of each equipment before starting work every day, including brushing machines, various ovens, exposure machines, and developing machines,
Weekly maintenance content project. Such as operating temperature, pressure, transmission speed, liquid concentration, wear scar width, a variety of switch valves, filter cleaning, filter replacement, ventilation, all kinds of indicator instruments.
(4) Check and record the first sheet of new solder mask before mass production. The first board check and record before character batch printing.
(5) Record the number of times the solder mask is used. Whether the rejected film is still in use. $Page break $
8. Check and test project.
According to the provisions of IPC桽M-840C, IPCæ¡00E, IPC桼B?7, and practical applications of domestic and foreign customers, review one
The basic requirements for solder masks and characters on printed boards.
Product Category: Level 1, refers to general electronic products, such as consumer products; Level 2, for specialized electronic products, including communications equipment. Complex business machines and instruments; Level 3, high-reliability electronic products; Continual operation, functional requirements of commercial supplies and military equipment, life-related equipment, and control systems.
8.1 Solder Mask
(1) Coverage over conductors
Skips, voids, blisters, and exposed wires are not allowed.
Smooth and uniform color, no obvious accumulation, no wrin-kles, waves, RIpples.
(2) Solder mask Land Registration To Lands
The clearance of the pad against the pad, metallized hole should be ≥ 0.05mm. Non-metallized holes ≥ 0.15mm. The clearance of the metallized hole pad and the pad, at least 270 degrees to maintain O. 05mm; The clearance between the non-metallized hole pad and the solder mask is at least 270° to keep O. 15mm, received on the 1.2th board, and the 3rd board refused.
Solder resistance is not allowed to enter the component hole and is not allowed to enter the SMT pad. Adhesive residue on the pad is not allowed.
(3) solder mask adhesion.
3M standard adhesive tape for adhesion test, allowing the maximum area of ​​the stripped tape to have solder mask
PCB surface coating Product classification Nickel-copper, substrate (%) Nickel/gold (%) Lead-tin (%)
Level 1 10 25 50
Level 2 0 5 20
Level 3 0 5 10
(4) Solder mask thickness
Level 1: Visual coverage is complete. Level 2: 30 to 40 μm on the substrate, ≥ 10 μm on the wire, and ≥ 10 μm on the edge of the wire. Level 3: ≥ 17.5 μm on the wire.
(5) Solder mask hardness
Pencil hardness ≥ 6H, 6H pencil test, solder mask should not be scratched.
(6) Solder mask Blqck Viaholes
95% of vias are required to be plugged. It is required that there be lead-tin through-holes in the hole, and the solder resist may not enter the hole.
(7) Condnctor Expose, copper Dirty under solder mask
The conductors must not be exposed to copper. Even in the area of ​​parallel conductors, variations in solder resist should not expose adjacent conductors. The copper surface under the solder mask has no obvious oxide layer water traces, and 3M tape test has no traces of shedding.
(8) Solder Mask Be-tween two SMT Lands
The distance between the two SMT pads should be ≥0.25mm, and the solder mask should be covered.
(9) Forelgn inclusions on solder mask
The sundries meet the following conditions and can be accepted: The sundries are insulators, and the impurity length is ≤1mm. If the insulation is ≥1mm, it needs to be removed if the copper is exposed.
It should be replenished.
(10) Touch Soide mask
The total is based on customer requirements. The general processing principle: the board size ≥ 160 × 100mm, can make up 3 points; <160 × 100mm
Can make up 2 points. The maximum size of the oil filling area: 2 × 5mm. Line exposed copper ≤ 2mm. Drying after oil replenishment, uniform color, no obvious heap
Product, 3M tape test can not go oil.
(11) Blisters, Bubbles (Blisters, Bubbles)
Can be allowed in each plate surface there are two, the bubble diameter is less than O. 25mm, bubbles should not cause bridging between wires.
(12) Solder mask on gold Fin-ger
At the junction of the gold finger and the solder resist, soldering can be performed in the root area A, but each board is less than 2 fingers. See figure 10.
No copper exposure is allowed at the intersection of gold finger and solder resist.
(13) Thermal Shock: Temperature -65 to 125°C. The number of loops is 100, no bubbles, splits or stratification.
(14) Resistance to soleler: On the hot air leveler, 255~265°C, 3 seconds, 3 times, the solder mask is intact, no blistering, discoloration, and film failure.
(15) Acid resistance: sulfuric acid or hydrochloric acid, concentration of 1O%, at room temperature, 60 minutes, no change in solder mask.
(16) Insulation resistance: 5×10 ohms or more.
(17) Flammability: VL 94VO class.
(18) Dielectric strength ≥ 500 VDC.
(19) Resistant to solvents and cleaning Agents
Samples were soaked in the following solvents/cleansers and allowed to dry at room temperature for 10 minutes. Observations should not be made for rough, blistering, splitting, swelling, discoloration, etc.
8.2 character (chara cfer)
(1) The ideal goal.
Characters are complete, clear, uniform, and hollow spaces are not filled, such as O. 6.8,9, A, B, D, cannot be changed to 0,6,8,9,A,B,D.
(2) Receive
• Letters, digits, and lines are incomplete, but they are still identifiable.
• The hollow area of ​​the character is altered, not yet identified, and will not be confused with other characters.
• The ink deposits appear on the outer edges of the characters, but the fonts have not yet been identified.
(3) Failed.
• The character is lost and cannot be identified.
· The hollow area of ​​the character is altered and cannot be read, resulting in misreading.
· Character lines have been blurred, incomplete, and lost, so that they cannot be discerned.
• The character appears to have a heavy shadow but is still identifiable and has also been found to be unqualified.
(4) Character pad, no. However, the customer agrees that it can be used as a special exception. It can be used as a pad on the park, but it must not be on the SMT pad.
(5) character adhesion, solvent resistance.
· 3M tape test, no word drop.
·Acetone wipe, no word drop.
The requirement character is a permanent ink.
(6) character color (white, yellow, black, etc.), type (thermoset, uv type), version number to be consistent with the requirements of the work card, and confirm whether it is single-sided or double-sided characters, is printed on the SS The (welded) surface is also the CS (component) surface, or double-sided printing.
(7) Character entry hole.
Characters are not allowed to enter the component hole and can be inserted into the through hole.
Solvents / Cleaners 1 2 3 4 5 6
Isopropall 75% Isopropanol/25% Water D-Lindene 10% Alkaline Detergent 90% Water (Alkaline Detergent) eg ≤40% Alkanolamine ≤20% 2 ~5 Ethoxylate Alcohol ≤ 20% Monoe thanolamine Deionized Water
Test Conditions Temperature Standards Laboratory Temperature 46±2°C Standard Laboratory Room Temperature 57±2°C(PH≤13) 57±2°C 60±2°C
Time (minutes) 2 15 2 2 2 5
(8) Check the work card, check the UL mark on the printed board, and if the company's mark is etched on the board, or whether the company's mark is printed on the board, whether the mark expression meets the requirements.
(9) In mass production, character printing must be checked on the first board, including all the above projects.
$Page break $9, curtain coating resistance welding overview.
9.1 Curtain Coating Features
Solder masks on printed boards come in a variety of forms. Screen printing described in this chapter is one of them. Actually, roll coating and spray coating are also used by companies. Curtain coating is also a form of resistance welding. In western countries, circuit board factories with a level of resistance have generally adopted curtain coating soldering. In recent years, some companies in Hong Kong, Taiwan and Guangdong have also developed curtain coating solder masks. Why Curtain coating?
(1) Small holes, fine lines, double-sided SMT, high-density double-sided multi-layer printed boards, screen printing liquid photoimprinting solder resist inks difficult to overcome fine
The phenomena of skipping between dense lines, the line is often easy to produce exposed copper, conductive phenomenon, line corner welding resistance occurs. Curtain coated solder resists these drawbacks.
(2) Curtain coating Solder is more suitable for large-scale continuous production. Brush plate curtain pre-baking together, easy to operate, high efficiency, automation, continuous operation 24 hours a day, people save.
(3) The quality of the curtain coating solder mask can meet the requirements of the US military standard. Many customers of European and American major electronics companies require, must or priority
Use curtains to apply solder mask, otherwise do not place orders.
9.2 Kinds of Curtain Ink
(1) Solvent type.
It is represented by the Ciba Cup eigy headquartered in Switzerland. Its model is the probimer 52, this ink has been tested in practice for nearly 20 years, its performance in line with the US military standard, has become the ink of choice for many high-end electronic products. This type of ink is epoxy type and can withstand a variety of chemical nickel/gold plating processes. The disadvantages are: it is a solvent type, requires a dedicated developer and a special developer, and requires a supporting solvent recovery device; the exposure speed is slow, and a 5kw exposure machine completes one panel exposure in 3 minutes.
(2) Water solvent.
This is a variety developed in recent years, such as ciba pro-bimer71, coates XV500, peter Elpemer G1?461,
aTaiyo company, etc., can overcome the shortcomings of solvent-based ink, developed with 1% anhydrous sodium carbonate solution, exposure speed and screen printing photosensitive ink,
No special solvent recovery equipment is required, saving investment in local and equipment, and the quality and performance are similar to those of solvent type. Curtain coating speed can reach about 150 ~ 200 puzzle / hour, usually 3 puzzle / points, puzzle size is 610 × 460mm (24 "18"). Of course, this curtain coating method also needs to be operated under yellow light conditions.
Curtain coating and screen printing solder mask thickness comparison shown in Figure thirteen.
9.3 Process Flow
Into the plate → pickling → washing → brush plate → washing → drying → flap → curtain coating solder (A surface) → observation → pre-baking (multi-stage) → cooling → flap → curtain coating solder (B surface) → Observe → pre-bake (multi-stage) → cooling plate ... → exposure
9.4 curtain coating resistance welding principle
See Figure XII. The curtain coating ink is contained in a funnel container (A), and the impurities of the ink are filtered through the screening procedure (B) and then pumped by the pump.
(D) is delivered to the spray head (F), and the ejected ink flows into the inner tank of the overflow tank (G), overflows to the outer tank, and then flows back directly to the collection tank (o) roller
(H) Rotate in the overflow. The scraper (I) scrapes off the ink which is continuously brought on the surface of the roller along the edge of the blade to form a solder mask curtain (L). Curtain screen welding
The ink is collected by the lower collecting trough and then returned to the storage tank (A) to form a closed loop.
The pre-treated PCB was passed through the curtain at a speed of 60 m/min, and its surface was coated with a uniform coating. Then put the board
Slow speed (about 1m/min), dried in an oven, and after completion of two-sided curtain coating, the printing plate can be exposed and developed. Complete the entire solder mask production process.
9.5 process points
The adjustment of the whole line involves more details, including surface treatment, wire thickness uniformity, curtain uniformity, ink viscosity, wet weight, macropore accumulation ink on the PCB, pre-bake adjustment, full-process control, equipment process maintenance Maintenance and other issues, this chapter is limited space, only an overview of the curtain coating welding