The grinding brush rollers used in PCB manufacturing process can be divided into two categories according to their functions, namely, grinding brush roller and cleaning brush roller, and nylon needle brush roller, non-woven cloth brush roller and ceramic brush roller according to the materials used. They have their own characteristics in use.
Nylon needle brush roller is divided into silicon carbide (SiC) abrasive class, alumina (AO) abrasive class and pure nylon class according to the nylon needle brush wire containing different abrasive class, non-woven brush roller is divided into silicon carbide, alumina and pure non-woven class according to the non-woven cloth containing different abrasive class. The nylon needle brush roller is characterized by long service life and moderate grinding effect. It is especially suitable for surface treatment in PCB manufacturing process when the line width/line distance (L/S) is greater than or equal to 8mil and the copper foil thickness is greater than or equal to 35um. Nonwoven brush roller is characterized by fine grinding and uniform and meticulous surface roughness of copper foil, which can significantly improve the adhesion of photosensitive film and solder resistance film. It is especially suitable for PCB surface treatment with line width/line distance less than or equal to 4mil and copper foil less than or equal to 35um.
Both nylon needle brush and non-woven roller can be used for grinding before dry film and green oil process.according to my working experience, the application and configuration of brush roller in each process are summarized, and I would like to discuss the problem of grinding with friends who are concerned about this problem.
- 1. Deburring after drilling (PTH)
- Objective: To provide clean surface for chemical copper sinking process by grinding to remove the edge of the hole, the dirt in the hole and the sundries and oxides on the surface of the plate.
- Requirements: After grinding, the surface roughness is required to be qualified, that is, the roughness is controlled at (2.0 – 3.5um), the surface has no serious scratches, no warping and no copper on the edge of the hole, good removal of the drape edge, no obvious drape edge under the ten-fold mirror, clean the surface without glue stains and oxides.
- Common problems: if the grinding is poor or excessive will cause obvious scratches on the surface, the surface oxidation, debris removal is not clean, the hole edge copper warping and no copper, resulting in copper plating off or more serious.
- Use parameters: 2×240#+2×320# (sic), abrasion mark: 10±2mm, water break: 15 seconds, roughness: 1.5 — 3.5um
- 2. Pre-treatment of Dry Film
- Objective: To obtain A uniform and meticulous grinding of the plate surface by grinding the surface of the plate to remove the copper particles, copper nodules and copper wires caused by the insufficient filtration of the liquid in the plate electrical process or other reasons, and to provide A good grinding effect for the film.
- Requirements: the surface of the board after grinding should be free of oxidation, debris, water marks;The roughness is controlled at 1.5-3.0um. For the surface processing technology, the roughness should be controlled at 1.5-2.5um in the electroplating copper-tin process, and the copper surface has no obvious scratches when observed under a 10x mirror, and the surface has no obvious color difference and uneven grinding phenomenon. And the brush roller is equipped according to the brightness of the gold surface required by the customer.Water film test for more than 15 seconds, no edge of the hole, grinding plate stored in the standard temperature and humidity environment (that is, the temperature of 20±2℃; Humidity 50±10%) no oxidation within 3 hours, hole edge copper cutting loss to meet the requirements.
- Common problems: if the grinding is poor or excessive will lead to the green oil on both sides of the Yin and Yang color, surface scratches or tail phenomenon.ROUGHNESS is not enough to send and receive green oil and copper surface combination is not good, hot air flat welding pad, chemical nickel gold and other surface processing process caused by green oil, infiltration, can not meet the tensile force and tin immersion test or the surface of the water, oxide, debris and other influences on the appearance.
- Use parameters: 2×500#+2×600# (sic), abrasion mark: 10±2mm, roughness: 1.5-2.5um, water break: more than 15 seconds.
- 3. Green oil pretreatment (Wet Film)
- Purpose: To grind the surface of the plate to meet the requirements and results of green oil printing.Surface oxidation and debris are removed by grinding to form a certain roughness.
- Requirements: no oxidation, debris, water mark on the surface after grinding;The roughness is controlled at about 2.0. Roughness should have no obvious fluctuation, the surface of the grinding plate without color difference, the surface of the plate without visible scratches. Put the fine circuit board along the grinding side, so as not to cut off or scratch the line; Water film test for more than 15 seconds, stored in the standard temperature and humidity environment (temperature 20±2℃, humidity 50±10%) within 3 hours without oxidation. Pay attention to high pressure washing pressure to avoid copper powder blocking between lines, causing short circuit. The appearance is uniform and meticulous, without obvious trailing; The copper wear of orifice should meet the requirements.
- Common problems: if the grinding is poor or excessive will lead to the green oil on both sides of the Yin and Yang color, surface scratches or tail phenomenon.The roughness is not enough to cause the combination of green oil and copper surface, hot air leveling, chemical nickel gold and other surface processing technology caused by green oil, infiltration, can not meet the tensile force and tin immersion test or the surface of the water, oxide, debris, etc., affect the appearance.
- Use parameters: 2×500#+2×600# (sic), abrasion mark: 10±2mm, roughness: 1.5-2.5um, water break: more than 15 seconds.
- 4. Gold Finger
- Objective: To provide clean and oxidation free copper surface for gold finger electroplating. It provides good electroplating conditions for electroplated fingers.
- Requirements: the grinding finger position should be free from oxidation, glue stains, no obvious scratches under 20 times the mirror, do not over grinding to prevent the finger position copper warping, falling off and serious scratches.
- Common problems: excessive grinding will cause finger gold surface rough, copper warping, scratches, infiltration plating;Poor grinding will cause gold surface oxidation, gold surface star-spot copper exposure, gold surface rough, gold surface matte color, color difference, can not meet the gold surface tensile and tin dipping test, gold layer fall off and other defects.
- Use parameters: 2×1000#+2×1200# (sic)
- 5. Chemical precipitation nickel gold pretreatment
- Objective: To remove the oxides and sundry things on the solder pads, IC feet and BGA position needed to deposit nickel gold by grinding method, or the residual chemical solvents due to the unclean development in the anti-welding process, so as to provide the required clean, uniform and fine copper surface for the next deposition of nickel gold.
- Requirements: usually in the production process are first printed welding resistance and then sink nickel gold process, so we need to take into account that we can not rub the welding resistance surface, the roughness can not be too high, the oxide layer, debris, residual chemical solvents and other clean, in the choice of brush roller configuration, we need to take into account both.Because the deposited nickel gold layer is lower than the solder resistance layer, the elastic nylon needle brush can only be used for this kind of surface treatment. Considering the attack of abrasive to the solder resistance layer, it is suggested that the plate be treated with UV light curing to improve the hardness of the solder resistance layer, so that it will not be easily rubbed.
- Common problems: first of all, improper selection of brush roll mesh and operation parameters will cause scratching, tarnishing, infiltration and can not meet the resistance of welding force and tin dip test;Or the roughness is too high and cause the gold surface roughness. If the number of brush rolls is too small and the grinding mark is too narrow on the surface of poor grinding, due to the oxide layer on the surface, residual solvent debris, glue stains and so on will cause rough gold surface, gold surface exposed copper, gold surface debris, plating off, leakage and other defects.
- Use parameters: 2×1000#+2×1200# (sic), abrasion mark: 8±2mm, roughness: 1.5 — 2.0um
- 6. Remove the blackened layer and the excess resin in blind hole after lamination/remove the excess resin in buried hole and the orifice leveling after screen printing.
- Objective: to eliminate the overflow of more than coy resin in the hole of the buried hole plate made by laminating or screen printing by high cutting and grinding brush roller, so as to achieve the flatness of the plate surface and the orifice, and meet the requirements of the production process and the characteristics of the buried hole.
- Requirements: Blind Via and Buried Via after grinding have flat orifice, no residual glue stains on the edge of the orifice, and clean blackened layer. In order to ensure that the blackened layer in lamination and the indentation of the substrate is clean, it is better to treat the plate with micro external erosion.The cutting loss of the orifice and surface copper layer meets the requirements (that is, the orifice: about 1-2um, the copper surface: about 0.5-1um). The copper layer is ground evenly and carefully. Brush roller smoothness and machine in good condition.
- Common problems: the brush roller cutting force is too large or too small, resulting in the hole edge resin removal, black layer removal, orifice copper cutting too much or orifice without copper, black spots in the surface dents, uneven wear marks resulting in uneven resin removal, uneven copper consumption, local orifice and plate without copper.
- Use parameters: Blind hole: 2×320# (hard C3)+2× 320# (hard C3)+2×600# (hard C3)+2×600# (hard C3), abrasion mark: 8-10mm,Buried hole: 2×240#(hard C3)+2× 240#(hard C3)+2× 240#(hard C3)+2×600#, abrasion mark: 8-10mm,
- 7. Removal of debris and residual resin of stainless steel plate for laminating
- Objective: To remove the glue stains, resins and sundry things on the steel plate after laminating by grinding method, so as to achieve clean and smooth effect and meet the quality requirements of laminating.
- Requirements: high temperature and high pressure in laminating production lead to resin overflow to the steel plate, or the medium on the debris and glue stains will cause the surface concave, dents, wrinkles and other defects to the post-production difficulties;In serious cases, the product will be scrapped. Therefore, the steel plate after grinding should be smooth, clean, no obvious scratches and granules under the 10 times mirror.
- Common problems: resin and debris not removed, will cause the plate surface dents, concave points seriously affect the qualified rate of later production.The steel plate is scratched seriously, which also causes the plate surface concave, and the copper layer perforated layer exposes the substrate, which also has a certain influence on the impedance value of the plate.
- Use parameters: high cutting nonwoven brush roller: 2×320#+2×320#+2×600#+2×600#
