PCB Tech - Causes of PCB Process Defects and Elimination Methods---Drilling

The first two articles on process defect problems and solutions mainly talked about substrates and negatives. This article focuses on some of the problems and solutions of the drilling process! Drilling is an important process in the PCB process, and it seems very simple. But in fact it is a very critical process. It is also prone to various problems.

One. Hole position offset, misalignment

(1) The drill bit shifts during the drilling process. Solution: A. Check whether the spindle is deflected. B. Reduce the number of stacked plates. In general, the number of double-sided laminates is 5 times the diameter of the drill bit, and the number of multilayer laminates is 2-3 times the diameter of the drill bit. C. Increase the speed of the drill bit or reduce the feed rate; D. Recheck whether the drill bit meets the process requirements, otherwise re-sharpening; E. Check whether the drill tip has good concentricity; F. Check the fixation between the drill bit and the collet chuck Whether the state is tight; G. Re-check and correct the stability and stability of the drilling table.

(2) Improper selection of cover material, soft and hard discomfort. Solution: Choose composite cover material (the upper and lower layers are aluminum alloy foil with a thickness of 0.06mm, the middle is a fiber core, and the total thickness is 0.35mm).

(3) Displacement due to expansion and contraction of the base material Solution: Check other operations after drilling, such as drying before boring

(4) Improper use of the matching positioning tool. Solution: Check or detect the dimensional accuracy of the tool hole and whether the position of the upper positioning pin is offset.

(5) Improper hole inspection procedures. Solution: Check hole inspection equipment and tools.

(6) Resonance occurs during the operation of the drill. Solution: Choose a suitable drill speed

(7) The spring chuck is dirty or damaged. Solution: Clean or replace the spring chuck.

(8) The drilling program is faulty. Solution: Recheck the tape, floppy disk and tape reader.

(9) The accuracy of the positioning tool system is insufficient. Solution: Detect and improve the tool hole position and hole diameter accuracy.

(10) The drill bit slips when it touches the cover plate. Solution: Choose a proper feed rate or a drill bit with better flexural strength.

Two. Aperture distortion

(1) The size of the drill bit is wrong. Solution: Before operation, check whether the size of the drill bit and the commands of the control system are normal.

(2) The feed rate or speed is not appropriate. Solution: Adjust the feed rate and speed to the most ideal state

(3) Excessive wear of the drill bit. Solution: Replace the drill bit and limit the number of holes for each drill bit. Usually 6000-9000 holes can be drilled according to double-sided boards (three pieces per stack); 500 holes can be drilled on high-density multilayer boards; 3000 holes can be drilled for FR-4 (three pieces per stack); and for harder ones FR-5, an average reduction of 30%.

(4) The number of drill regrinding is too many or the chip flute is long. Solution: Limit the number of drill regrinding and the degree of regrinding below the standard regrinding size change. For drilling multi-layer boards, sharpening once for every 500 holes drilled, 2-3 times of sharpening is allowed; once for every 1000 holes drilled; once for every 3000 holes drilled for double panels, sharpening once, then drilling 2500 holes; then sharpening Drill 2000 holes at a time. Re-grinding the bit in time can increase the number of bit re-grinding and increase the life of the bit. Measured by a tool microscope, the wear depth within the full length of the two main cutting edges should be less than 0.2mm. When regrinding, 0.25mm should be removed. Fixed shank drills can be reground 3 times; spade-shaped drills can be reground 2 times.

(5) Excessive deflection of the drill shaft. Solution: Use a dynamic deflection tester to check the deflection of the main shaft during operation or repair it by a professional supplier when it is serious.

Three. Excessive drilling of debris in the hole wall

(1) The feed rate or rotation speed is not appropriate. Solution: Adjust the feed rate or rotation speed to the highest state.

(2) Substrate resin polymerization is not complete. Solution: Before drilling, it should be placed in an oven at a temperature of 120°C and bake for 4 hours.

(3) The drill bit hits for several times and the loss is excessive. Solution: The number of holes for each drill bit should be limited.

(4) The drill has too many regrind times or the length of the chip flute is lower than the technical standard. Solution: The regrind times should be specified in the process and the technical standards should be implemented.

(5) The material quality of the cover plate and the backing plate is poor. Solution: Choose the cover plate and backing plate materials specified by the process.

(6) The geometric shape of the drill bit is problematic. Solution: The geometric shape of the detected drill bit should meet the technical standards.

(7) The drill bit stays in the base material for too long. Solution: Increase the feed rate and reduce the number of laminate layers.

Four. Protruding glass fiber in the hole

(1) The retraction rate is too slow. Solution: The best retraction rate should be selected.

(2) Excessive wear of the drill bit. Solution: The number of drill holes should be limited in accordance with the process regulations and regrind after testing.

(3) The spindle speed is too slow. Solution: According to the formula and actual experience, readjust the best data between the feed rate and the spindle speed.

(4) The feed rate is too fast. Solution: Reduce the feed rate to the appropriate rate data.

Five. Excessive nail heads in the inner ring

(1) The retraction speed is too slow. Solution: Increase the retraction speed to the maximum state.

(2) Inappropriate feed rate setting. Solution: Reset the feed rate to achieve the maximum value.

(3) Excessive wear of the drill bit or inappropriate use. Solution: Limit the number of holes drilled by the drill bit in accordance with the process regulations, re-sharp the drill bit after testing, and select a suitable drill bit.

(4) The spindle speed does not match the feed rate. Solution: According to experience and reference data, adjust the feed rate and drill bit speed to the best state and detect the variation of the spindle speed and feed rate.

(5) There are defects such as voids in the substrate. Solution: The defects of the substrate itself should be replaced with high-quality substrate materials immediately.

(6) The surface tangent speed is too fast. Solution: Check and correct the surface tangent speed.

(7) Too many laminate layers. Solution: Reduce the number of laminate layers. The thickness of the laminated board can be determined according to the diameter of the drill bit. For example, the double-sided board is 5 times the diameter of the drill bit; the thickness of the multi-layer laminated board is 2-3 times the diameter of the drill bit.

(8) Poor quality of cover plate and backing plate. Solution: Use cover and backing plate materials that are less prone to high temperatures.

Six. A white circle appears on the edge of the hole (the copper layer on the edge of the hole is separated from the substrate)

(1) Thermal stress and mechanical stress generated during drilling caused localized chipping of the substrate. Solution: Check the wear of the drill bit, and then replace or regrind it.

(2) The size of the glass cloth weaving yarn is relatively thick. Solution: The glass cloth woven from fine glass yarn should be used.

(3) The quality of the substrate material is poor. Solution: Replace the substrate material.

(4) The feed amount is too large. Solution: Check whether the set feed amount is correct.

(5) The drill bit is loose and not tightly fixed. Solution: Check the diameter of the drill bit shank and the tension of the spring chuck.

(6) The number of laminate layers is too much. Solution: Adjust according to the laminate data of the process regulations.

Seven. Rough hole wall

(1) The feed amount has changed too much. Solution: Keep the highest feed rate.

(2) The feed rate is too fast. Solution: Adjust the feed rate and speed according to experience and reference data to achieve the best match.

(3) Improper selection of cover material. Solution: Replace cover material.

(4) The vacuum degree of the fixed drill is insufficient. Solution: Check the vacuum system of the CNC drilling machine and check whether the spindle speed has changed.

(5) The retraction rate is not suitable. Solution: Adjust the retraction rate and drill speed to reach the maximum state.

(6) The cutting edge of the top corner of the drill is broken or damaged. Solution: Check the use status of the drill or replace it.

(7) The deflection of the spindle is too large. Solution: Check and clean the spindle and spring chuck.

(8) Poor chip discharge performance. Solution: Improve chip discharge performance and check the state of chip flutes and cutting edges.

Eight. The hole wall burr is too large, which has exceeded the standard data

(1) The drill is not sharp or the first face angle (referring to the cutting edge) is worn. Solution: According to the detection situation, decide to re-sharp or replace the drill. Must be tested before use.

(2) There is foreign matter between the stacked plates or the fixing is not tight. Solution: Before stacking the plates, check the surface cleanliness carefully. Tighten the stack when installing it to reduce foreign matter between the stacks.

(3) The feed amount is selected too large. Solution: The maximum feed amount should be re-selected based on experience and reference data.

(4) Improper selection of cover thickness (too thin) Solution: Use thicker cover material with appropriate hardness.

(5) The pressure of the pressure foot of the drilling machine is too low (fuzzes are produced in the hole of the upper plate) Solution: Check the pressure of the pressure foot of the drilling machine, springs and seals

(6) The quality of the substrate material to be drilled is poor (burrs appear on the bottom hole of the substrate) Solution: Choose a cover plate material with suitable hardness and flatness.

(7) Loose positioning pins or poor verticality. Solution: Replace positioning pins and repair worn molds.

(8) Dust appears in the positioning pin hole. Solution: It must be cleaned carefully before the positioning pin is installed.

(9) The substrate material is not fully cured (burrs appear at the exit of the drilling plate) Solution: Before drilling, it should be baked at 120°C in an oven for 4-6 hours.

(10) The hardness of the backing plate is not enough, causing the chips to be brought back into the hole. Solution: Choose the backing plate material with suitable hardness.

Night. Debris on the hole wall

(1) The material of the cover plate or substrate is inappropriate. Solution: Select or replace the appropriate cover plate and substrate material.

(2) The cover plate causes damage to the drill bit. Solution: Choose a cover plate material with appropriate hardness. Such as No. 2 rust-proof aluminum or composite material cover.

(3) Insufficient vacuum pressure of the collet chuck of the fixed drill. Solution: Check the vacuum system (vacuum degree, pipeline, etc.) of the machine.

(4) The air supply pipe of the pressure foot is blocked. Solution: Replace or clean the pressure foot.

(5) The helix angle of the drill bit is too small. Solution: Check whether the drill bit meets the standard technical requirements.

(6) The number of laminate layers is too much. Solution: The number of laminate layers should be reduced in accordance with the process requirements.

(7) The drilling process parameters are incorrect. Solution: Choose the best feed speed and drill bit speed.

(8) The environment is too dry to produce electrostatic adsorption. Solution: According to the process requirements, the specified humidity should be reached and the humidity should be above 45% RH.

(9) The retraction rate is too fast. Solution: Choose a suitable retraction rate.

Ten. The roundness of the hole shape is inaccurate

(1) The main shaft is slightly bent and deformed. Solution: Check or replace the bearing in the main shaft.

(2) The center point of the drill bit is eccentric or the width of the two cutting edge surfaces is inconsistent. Solution: Use a 40x microscope to check before clamping the drill bit.

Eleven. The crimped debris with broken wires is found on the board surface above the laminated board

(1) No cover plate is used. Solution: A suitable cover plate should be used.

(2) Improper selection of drilling process parameters. Solution: Generally, you should choose to reduce the feed rate or increase the drill bit speed.

Twelve. The drill is easy to break

(1) Excessive spindle deflection. Solution: The spindle should be overhauled and restored to its original state.

(2) Improper operation during drilling. Solution: A. Check whether the pressure beriberi pipe is blocked. B. Adjust the pressure of the pressure foot according to the status of the drill bit. C. Check the spindle speed variation. D. Check the stability of the spindle while drilling is in progress.

(3) Inappropriate drill bit selection. Solution: Check the geometric shape and wear of the drill bit and select a drill with an appropriate chip-reducing groove length.

(4) The speed of the drill is insufficient, and the feed rate is too high. Solution: Choose a proper feed rate and reduce the feed rate.

(5) The number of laminate layers is too high. Solution: Reduce to a suitable number of laminate layers.

Thirteen. Hole position deviation causes broken or partial ring

(1) The drill bit swings so that the center of the drill bit cannot be aligned. Solution: A. Reduce the number of stacks of the substrate to be drilled. B. Increase the speed and reduce the feed rate. C. Check the angle and concentricity of the drill bit. D. Observe whether the position of the drill bit on the collet chuck is correct. E. The length of the drill chip flute is not enough. F. Correct and adjust the alignment and stability of the drilling rig.

(2) The hardness of the cover is high and the material is poor. Solution: Choose a cover material that is uniform and smooth and has heat dissipation and positioning functions.

(3) The substrate is deformed after drilling and the hole is offset. Solution: According to production experience, the substrate before drilling should be baked.

(4) Error in the positioning system. Solution: Check the positioning hole accuracy of the positioning system.

(5) Poor alignment during manual programming. Solution: Check the operating procedure.

Fourteen. Wrong aperture size

(1) Data input error occurred during programming. Solution: Check whether the aperture data entered in the operating program is correct.

(2) Misuse the drill with the wrong size for drilling. Solution: Check the diameter of the drill and replace the drill with the correct size.

(3) Improper use of the drill bit and serious wear. Solution: When replacing a new drill bit, limit the number of holes drilled by the drill bit in accordance with the process regulations.

(4) The drill bit used has too many times of regrind. Solution: The geometric dimension changes of the drill bit after regrind should be strictly checked.

(5) Misreading the aperture requirements or errors in the conversion of the English system to the metric system. Solution: Read the blue chart carefully and convert carefully.

(6) When the drill bit is automatically changed, the drill bit is arranged incorrectly. Solution: Check the size sequence of the drill bit before drilling.

Fifteen. The drill bit is easy to break

(1) Improper operation of the CNC drill. Solution: A. Check the pressure data when the pressure foot is pressed. B. Carefully adjust the state between the pressure foot and the drill bit. C. Detect the change of the spindle speed and the stability of the spindle. D. Check the parallelism and stability of the drilling table.

(2) Cover plate and backing plate are not flat. Solution: Choose a cover and backing plate with appropriate surface hardness and flatness.

(3) The feed speed is too fast to cause extrusion. Solution: Appropriately reduce the feed speed.

(4) The depth of the drill bit into the backing plate is too deep, and the strangulation occurs. Solution: The depth of the drill bit should be adjusted in advance.

(5) The tape is not firmly attached when fixing the substrate. Solution: Check the fixing status carefully.

(6) Improper operation especially when filling holes. Solution: Pay attention to the correct position of filling holes during operation.

(7) Too many laminate layers. Solution: reduce the number of laminate layers

Sixteen. Hole plugging

(1) The length of the drill bit is not enough. Solution: Choose an appropriate drill bit length according to the thickness of the stack.

(2) The depth of the drill bit into the backing plate is too deep. Solution: The laminated thickness and backing plate thickness should be selected reasonably.

(3) The problem of substrate material (moisture and dirt) Solution: a good quality substrate material should be selected, and the drilling should be baked.

(4) The result of repeated use of the backing plate. Solution: The backing plate should be replaced.

(5) Improper processing conditions. Solution: The best processing conditions should be selected.

Seventeen. Aperture expansion

(1) There is a problem with the drill diameter. Solution: The drill diameter must be checked carefully before drilling.

(2) When the drill bit is broken in the hole, the hole diameter becomes larger. Solution: Use the method of ejecting the drill bit that is broken in the hole.

(3) Caused when repairing leaks. Solution: Pay attention to the diameter of the drill bit when repairing holes.

(4) Error caused by repeated drilling of positioning holes. Solution: Re-select positioning hole position and dimensional accuracy.

(5) Caused by repeated drilling. Solution: Pay special attention to the diameter of the drilled hole.

Eighteen. The hole is not penetrated

(1) The DN setting is wrong. Solution: The program setting must be correct before drilling.

(2) The problem of uneven backing plate thickness. Solution: Choose a uniform and appropriate backing plate thickness.

(3) There is a problem with the set length of the drill. Solution: Set or choose a suitable length according to the thickness of the stack.

(4) The drill bit is broken in the hole. Solution: Check the stacking and clamping status and process conditions before drilling

(5) Improper selection of cover thickness. Solution: Choose cover material with uniform thickness and appropriate thickness.