It is impossible to manufacture any number of printed circuit boards without encountering some problems, some of which are due to the quality of the copper clad laminate material. When quality problems arise during actual manufacturing, it is often because the substrate material is the cause of the problem. Even a carefully written and implemented laminate specification does not specify the tests that must be performed to determine that laminate is the cause of a manufacturing process failure. Here is a list of some of the most commonly encountered laminate problems and how to confirm them.
As soon as laminate issues are encountered, an addition to the laminate specification should be considered. Usually, if this specification is not enriched, it will result in continuous quality changes and subsequent product scrapping. Typically, material issues due to variations in laminate quality occur between manufacturers using different batches of raw material or products made with different press loads. Few users maintain sufficient records to be able to identify specific press loads or batches of material at a PCB processing facility. It then often happens that printed circuit boards are continually produced and loaded with components, and warpage continues to occur in the solder bath, thereby wasting a great deal of labor and expensive components. If the batch number of the charge is immediately known, the laminate manufacturer can check the batch number of the resin, the batch number of the copper foil, the curing cycle, etc. In other words, if the user cannot provide continuity with the quality control system of the laminate manufacturer, it will cause the user himself to suffer losses in the long run. The following describes general issues related to substrate materials during the manufacture of printed circuit boards.
1. Superficial problems
Symptoms: Poor printing adhesion, poor coating adhesion, some parts cannot be etched away, and some parts cannot be soldered.
Inspection method: usually use water to form visible water marks on the surface of the board for visual inspection, or use ultraviolet light to irradiate the copper foil to find whether there is resin on the copper foil.
possible reason:
(1) Due to the very dense and smooth surface caused by the release film, the uncoated copper surface is too bright.
(2) Usually on the non-copper side of the laminate, the laminate manufacturer does not remove the release agent.
(3) Pinholes on the copper foil cause the resin to flow out and accumulate on the surface of the copper foil, which usually occurs on copper foil thinner than the 3/4 ounce weight specification, or environmental problems cause resin powder on the copper foil The foil surface is laminated.
(4) Copper foil manufacturers apply excess antioxidants to the surface of copper foil.
(5) The laminate manufacturer changed the resin system, release film, or scrubbing method.
(6) There are many fingerprints or grease stains due to improper operation.
(7) When punching, blanking or drilling operations are stained with engine oil or otherwise polluted by organic matter.
Solution:
(1) It is recommended that laminate manufacturers use fabric-like films or other release materials.
(2) Contact the laminate manufacturer to use mechanical or chemical methods of elimination.
(3) Contact the laminate manufacturer to inspect each batch of unqualified copper foil; ask for the recommended solution to remove the resin to improve the manufacturing environment.
(4) Ask the laminate manufacturer for the method of removal. It is usually recommended to use hydrochloric acid followed by mechanical removal.
(5) Before making any changes in laminate manufacturing, cooperate with the laminate manufacturer and specify the user's test items.
(6) Educate all process personnel to wear gloves to handle copper clad laminates. Make sure that the laminates are shipped with proper pads or packed in bags, and the pads have low sulfur content, and the bags are free of dirt. Make sure no one touches them while using detergents containing silicones. Copper foil to keep the device in good condition.
(7) Degrease all laminates before plating or graphic transfer process.
2. Appearance problems
Symptoms: Laminates are visibly different in color, different surface colors, stains on the surface or inner layers, thin layers of various colors on the surface of the laminate.
Inspection method: visual inspection.
possible reason:
(1) There are white cloth patterns or white spots on the surface of the glass cloth-based laminate before PCB processing or after etching.
(2) After the process of PCB processing, white spots appear on the surface or more glass cloth is exposed.
(3) After PCB processing, especially after soldering, there is a thin layer of white film on the surface, which indicates that the resin is slightly etched or there are foreign deposits.
(4) The color change of the base material exceeds the acceptable appearance requirements.
(5) Because the laminate is overheated or soaked for a long time by some liquid medicine concentration, the appearance of the substrate will produce brown or brown spots.
Solution:
(1) In very rare cases, it is because of the lack of resin on the surface that the glass cloth is exposed, which is rare today. More often seen are tiny blisters or small white voids on the surface. This is caused by the reaction between the coating layer on the surface of the glass cloth and the resin system. The board with a lot of glass cloth exposed, the surface resistivity decreases when the humidity increases. Boards with micro-bubbles or small blisters, however, generally do not drop. Strictly speaking, this is just a matter of appearance. Deal with the laminate fabricator to prevent this from happening again; and determine acceptable internal standards for micro-bubbling.
(2) Most of the cases where the glass cloth is exposed after PCB processing is due to solvent erosion, which removes some surface resin. Verify with the laminate fabricator all solvents and baths, especially the time and temperature at which the laminate is in each solution, to ensure that they are suitable for the laminate being used. Follow the laminate manufacturer's recommended conditions for PCB processing where possible.
(3) Check with the laminate manufacturer to ensure that the flux used is suitable for the board used. Verify that processes that may deposit minerals or inorganic substances, where possible, use demineralized water where possible.
(4) Contact the laminate manufacturer to ensure that any major components or resins of the laminate (which affect color) are approved by the user before making changes. Sometimes excess copper alloy transfer can affect the color. Work with the laminate manufacturer to determine the range of acceptable appearance.
(5) Check dip soldering operation, solder temperature and stop time in solder bath. Also check the ambient temperature of the heating element on the printed board or the entire printed board. If the latter exceeds the upper limit of the allowable temperature of the laminate used, the substrate will develop a brown color. Boards that have been soaked for too long in some liquid medicine concentration will show up when the board is heated and tested in the post-process. Check and control the liquid medicine concentration and time.
3. Mechanical PCB processing problems
Phenomenon symptoms: inconsistent punching, shearing, and drilling PCB processing quality, poor coating adhesion or uneven coating in metallized holes.
Inspection method: inspect the incoming materials, test various key mechanical PCB processing operations, and carry out routine analysis after the incoming laminates are passed through the hole metallization process.
possible reason:
(1) Material curing, resin content, or plasticizer changes will affect the drilling, punching and shearing quality of the material.
(2) Poor drilling, punching or shearing techniques result in poor or inconsistent production quality.
(3) The preheating cycle time before punching or drilling is too long, which sometimes affects the PCB processing of the laminate.
(4) The aging of materials, mainly phenolic materials, sometimes causes the plasticizer in the material to run away, making the material more brittle than usual.
Solution:
(1) Contact the laminate manufacturer to establish tests that mimic key mechanical PCB processing performance requirements. The production tooling should not be used for the test, otherwise wear and changes in the production tooling will affect the test results. In any problem with mechanical PCB processing performance changes, only when the problem occurs at the same time as the material lot number change, can there be a problem with the quality of the laminate.
(2) Refer to the manufacturing recommendations for various types of laminates. Check with the laminate manufacturer for specific drill speeds, feeds, drill and punch temperatures for each grade of laminate. Remember: Every manufacturer uses a different mixture of resins and substrates, and their recommendations will vary.
(3) Preheat the laminate carefully, being sure to identify any overheated areas, such as under heat lamps. When heating materials, the principle of first in first out should be followed.
(4) Check with the laminate manufacturer to obtain the aging characteristic data of the material. Turnover stock so that the stock is usually newly produced panels. Be sure to check for possible overheating during warehouse storage.
4. Warping and twisting problems
Symptoms: The base material is warped or twisted before or after PCB processing or during PCB processing. Hole tilting after soldering is also a sign of substrate warping and twisting.
Inspection method: use float test, it is possible to carry out incoming inspection. Soldering tests with a 45-degree inclination are particularly effective.
possible reason:
(1) When receiving the goods or after sawing and trimming, the material is warped or twisted, which is usually caused by improper lamination, improper cutting or uneven laminate structure.
(2) Warpage can also be caused by improper storage of materials, especially paper-based laminates, which can bow or deform when placed vertically.
(3) The warping is caused by the unequal copper wall and iron wall foil. If one side is 1 ounce, the other side is 2 ounces: the electroplating layer is not equal, or the special printed board design causes copper stress or thermal stress.
(4) Improper fixtures or fixtures during soldering, and heavy components during soldering operations will also cause warping.
(5) During the process of PCB processing or soldering, the hole displacement or inclination on the material is caused by improper curing of the laminate or the stress of the glass cloth structure of the substrate.
Solution:
(1) Straighten the material or release the stress in the oven, and perform the cutting operation according to the inclination angle and the heating temperature of the board recommended by the laminate manufacturer. Check with the laminate manufacturer to ensure that a structurally uneven substrate is not used.
(2) Store the material flat in the loading cardboard box or lay the material obliquely on the shelf. Usually the material should be placed at an angle of 60 degrees or less with the ground.
(3) Contact the laminate manufacturer to avoid unequal copper foils on both sides. Analyze plating and stress, or localized stress caused by heavy components or large copper areas. Redesign the printed board to balance components and copper area. Sometimes most of the wires on one side of the printed board are laid vertically to the wires on the other side, so that the thermal expansion of the two sides is not equal and causes distortion. This kind of wiring should be avoided as long as possible.
(4) In the soldering operation, printed boards, especially paper-based printed boards, must be clamped with fixtures. In some cases, heavy elements must be balanced with special jigs or with fixtures.
(5) Contact the laminate manufacturer for any recommended post-curing measures. In some cases, the laminate manufacturer will recommend another laminate for a more stringent or specialized application.
5. Laminates have white spots or delamination
Symptoms: White spots or graining appear on the surface or in the material; either locally or over a large area.
Inspection method: Proper float test.
possible reason:
(1) During soldering, large areas of blistering are caused by moisture and volatiles pressed into the material. Poor mechanical PCB processing is also a factor, as it can delaminate the laminate and allow the laminate to absorb moisture during wet process PCB processing.
(2) White cloth lines or white spots are produced during soldering, which is due to the uneven structure of the laminate, improper curing of the laminate, poor stress release of the laminate, or poor ductility of electroplated copper.
(3) Fibers or serious white spots are exposed during soldering operations. This is due to excessive contact with solvents, especially chlorine-containing solvents, which can soften the resin.
(4) When the base material is heated, the tightly fixed big yuan or connection terminal will cause great stress on the plate. The result is white spots around this dense area. The plate is stressed during or after dip-soldering, and white spots will appear when it is flexed or bent.
Solution:
(1) Notify the laminate manufacturer that a batch of laminates with such problems has been found. Use recommended mechanical PCB processing methods for all board materials.
(2) Contact the laminate manufacturer for instructions on how to relieve the stress on the printed board before dipping. Storing printed boards under high humidity for a period of time will absorb excess moisture, which will affect the solderability of printed boards. Prebaking and preheating printed boards prior to solder dip operations to reduce thermal shock can help with both of these issues (see data on moisture absorption of stored printed circuit boards for multilayer materials).
(3) Contact the laminate manufacturer for the optimum solvent and application time. Validate all wet PCB processing processes, especially solvents, when substrates are changed.
(4) In wave soldering or manual soldering operations, loosen fastened terminal blocks and remove any heat sinks or heavy components before dip soldering. Check the correctness of mechanical PCB processing operations, especially punching operations, to ensure white spots and mild delamination caused by improper operations. Make sure the sheet is properly clamped and not stressed when heated. Do not quench printed boards in cooler flux remover while hot or under stress.
6. Adhesive strength problem
Symptoms and symptoms: During the dip soldering operation, the pads and wires are detached.
Inspection method: During incoming inspection, fully test and carefully control all wet PCB processing processes.
possible reason:
(1) The detachment of pads or wires during PCB processing may be caused by plating solution, solvent attack, or stress on copper during plating operations.
(2) Punching, drilling or piercing will partially detach the pad, which will become apparent during the hole metallization operation.
(3) During wave soldering or manual soldering operations, the detachment of pads or wires is usually caused by improper soldering techniques or excessive temperature. Sometimes the pads or wires are detached because the laminate is not well bonded or the thermal peel strength is not high.
(4) Sometimes the design and wiring of the printed board will cause the pads or wires to detach at the same place.
(5) During the soldering operation, the retained heat absorption of the components will cause the pads to detach.
Solution:
(1) Give the laminate manufacturer a complete list of solvents and solutions used, including processing time and temperature for each step. Analyze the plating process for copper stress and excessive thermal shock.
(2), earnestly abide by the recommended mechanical PCB processing method. Frequent analysis of metallized holes can control this problem.
(3) Most of the pads or wires are detached due to lax requirements for all operators. Detachment can also occur from a failed temperature test of the solder bath or from prolonged dwell time in the solder bath. In manual soldering trim operations, pad detachment is presumably due to the use of an electrochrome of the wrong wattage and a lack of professional process training. Some laminate manufacturers now manufacture laminates with high peel strength grades at elevated temperatures for severe soldering use.
(4) If the detachment caused by the design wiring of the printed board occurs in the same place on each board; then this printed board must be redesigned. Usually, this does happen where thick copper foil or wires are turned at right angles. Sometimes this happens with long wires; this is due to the difference in coefficient of thermal expansion.
(5) When possible, remove heavy components from the entire printed board, or install them after dipping. Careful soldering is usually done with a low wattage soldering iron, which heats the substrate material for a shorter duration than component dip soldering.
7. Various soldering problems
Symptoms and signs: There are blast holes in cold solder joints or tin solder joints.
Inspection method: Regularly analyze the holes before and after dipping to find out where the copper is stressed. In addition, carry out incoming inspection on raw materials.
possible reason:
(1) Blast holes or cold solder joints are seen after soldering operations. In many cases, poor plating followed by expansion during the soldering operation created voids or blow-out holes in the metallized hole walls. If this occurs during the wet PCB fabrication process, the absorbed volatiles are masked by the plating and then driven out by the heat of the solder dip, which can create vents or blast holes.
Solution:
(1) Try to eliminate copper stress. Expansion of laminates in the z-axis or thickness direction is usually material dependent. It can promote the fracture of metallized holes. Deal with the laminate manufacturer for recommendations on materials with less z-axis expansion.
8. The problem of excessive size change
Symptoms: After PCB processing or soldering, the substrate size is out of tolerance or cannot be aligned.
Inspection method: Fully carry out quality control during PCB processing.
possible reason:
(1) No attention has been paid to the structural texture direction of the paper-based material, and the forward expansion is about half of the horizontal expansion. Also, the substrate does not return to its original size after cooling.
(2) If the local stress in the laminate is not released, it will sometimes cause irregular dimensional changes during PCB processing.
Solution:
(1) Instruct all production personnel to always cut the board according to the same structural texture direction. If the dimensional variation is out of tolerance, consider switching to a substrate.
(2) Contact the laminate manufacturer for advice on how to relieve material stress before PCB processing.
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