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How to solve the quality problems of PCB substrates and laminates

Jul 23, 2018

It is impossible to manufacture any number of printed circuit boards without encountering some problems, some of which are attributed to the material of the copper clad laminate. When quality problems occur during actual manufacturing, it is often because the substrate material is the cause of the problem. Even a carefully crafted and practically implemented laminate specification does not specify the test items that must be performed to determine that the laminate is the cause of the production process. Here are some of the most commonly encountered laminate problems and how to confirm them. Once you encounter laminate problems, you should consider adding to the laminate specification. Often, if you do not carry out the work of enriching this technical specification, it will cause constant quality changes, which will lead to product retirement. In general, material problems arising from changes in the quality of the laminate occur in different batches of raw materials used by the manufacturer or in products manufactured using different pressing loads. Few users are able to hold a large enough number of records to distinguish specific compression loads or material batches at the processing site. As a result, it is often the case that printed circuit boards are continuously produced and mounted with components, and warpage is continuously generated in the solder bath, thereby wasting a lot of labor and expensive components. If the batch number is immediately available, the laminate manufacturer can check the batch number of the resin, the batch number of the copper foil, the curing cycle, and the like. That is, if the user is unable to provide continuity with the laminate manufacturer's quality control system, this will cause the user to suffer long-term losses. The general issues associated with substrate materials during the manufacture of printed circuit boards are described below.

 

I. Surface problems

It is now a symbol: poor adhesion of the printing material, poor adhesion of the coating, some parts cannot be etched away, and some parts cannot be soldered.

The inspection method can be used: usually, water is formed on the surface of the board to form a visible water mark for visual inspection, or irradiated with an ultraviolet lamp, and the copper foil is irradiated with an ultraviolet lamp to find out whether there is resin on the copper foil.

possible reason:

1. The very dense and smooth surface caused by the release film, causing the uncoated copper surface to be excessively bright.

2. Typically on the uncoated side of the laminate, the laminate manufacturer does not remove the release agent.

3. Pinholes on the copper foil, causing the resin to flow out and accumulate on the surface of the copper foil, which usually occurs on copper foils that are thinner than the 3/4 ounce weight specification, or environmental problems cause resin powder on the copper foil surface. After lamination.

4. The copper foil manufacturer applies an excess of antioxidant to the surface of the copper foil.

5. The laminate manufacturer changed the resin system, mold release, or brushing method.

6. There are many fingerprints or grease stains due to improper operation.

7. Oil, or other means of contamination with organic matter during punching, blanking or drilling operations.

Solution:

1. It is recommended that laminate manufacturers use fabric-like films or other release materials.

2. Contact the laminate manufacturer using mechanical or chemical removal methods.

3. Contact the laminate manufacturer to inspect each batch of unqualified copper foil; request a solution recommended by removing the resin to improve the manufacturing environment.

4. Ask the laminate manufacturer for the method of removal. It is recommended to use hydrochloric acid and then remove it mechanically.

5. Cooperate with the laminate manufacturer and specify the user's test items before making any changes to the laminate manufacturing.

6. Educate all personnel in the process to wear gloves and cover the copper plate. Make sure that the laminate is properly loaded or packed in the bag during transportation, and that the pad has low sulfur content and that the bag is free of dirt. Be sure to ensure that no one is using the silicone-containing detergent. Copper foil to ensure that the equipment is in good condition.

7. Degrease all laminates prior to plating or prior to the graphic transfer process.

 

        2. Appearance problems

It is now a symbol: the color of the laminate is obviously different, the surface color is different, the surface or the inner layer is stained, and there are thin layers of various colors on the surface of the laminate.

The inspection method that can be used: visual inspection.

possible reason:

1. Glass cloth based laminates have white or white spots on the surface before or after etching.

2. After the process is processed, white spots appear on the surface or more glass cloth is exposed.

3. After processing, especially after soldering, there is a thin layer of white film on the surface, which indicates that the resin is slightly etched or has a foreign deposit.

4. The color change of the substrate exceeds the acceptable appearance requirements.

5. The appearance of the substrate produces brown or brown markings due to overheating of the laminate or excessive soaking of certain syrups.

Solution:

1. In very rare cases, it is because the surface lacks resin and reveals glass cloth, which is rare today. More often seen are tiny blistering or small white cavities on the surface. This is due to the reaction of the surface coating of the glass cloth and the resin system. A plate with a lot of glass cloth is exposed, and the surface resistivity decreases as the humidity increases. However, boards with tiny blistering or small bubbling do not usually fall. Strictly speaking, this is just a matter of appearance dealing with laminate makers to avoid such problems; and to determine acceptable internal standards for tiny foaming.

2. Most of the exposed glass cloth after processing is due to solvent etching, and some surface resins are removed. All solvents and baths were inspected with the laminate manufacturer, especially the time and temperature of the laminate in each solution to ensure that they were suitable for the laminate used. When possible, process as recommended by the laminate manufacturer.

3. Check with the laminate manufacturer to ensure that the flux used is suitable for the sheet used. To verify the process by which minerals or inorganics may be deposited, in the process where minerals or inorganics may be deposited, whenever possible, mineral-depleted water is used.

4. Contact the laminate manufacturer to ensure that any major components of the laminate or resin (which have an effect on color) are approved by the user before making changes. Sometimes an excess of copper alloy transfers the color. Work with laminate manufacturers to determine an acceptable range of appearance.

5. Check the dip soldering operation, solder temperature and stop time in the solder bath. Also check the ambient temperature of the heating element or the entire printed board on the printed board. If the latter exceeds the upper limit of the allowable temperature of the laminate used, the substrate will produce a brown color. When the concentration of some syrups is too high, the immersed plates are displayed in the post-process heating test panel, and the concentration and time of the control syrup are checked.

 

3. Machining problems

Now it is a symbolic sign: the quality of punching, shearing and drilling is inconsistent, the plating adhesion is poor or the plating in the metallized holes is uneven.

Inspection method: Check the incoming materials, test various key machining operations, and carry out the conventional analysis after the laminate is subjected to the hole metallization process.

possible reason:

1. Material curing, resin content, or plasticizer changes will affect the drilling, punching and shear quality of the material.

2. Drilling, punching or shearing process is poor, resulting in poor or inconsistent production.

3. The preheating cycle time before punching or drilling is too long, sometimes affecting the processing of the laminate.

4. The aging of the material, mainly phenolic materials, sometimes causes the plasticizer to run away in the material, making the material more brittle than usual.

Solution:

1. Contact the laminate manufacturer to establish a test that mimics the critical machinability requirements. Production molds should not be used for testing, otherwise the wear and tear of the production mold will affect the test results. Among any problems with changes in machinability, the problem is that the quality of the laminate is suspected only if the problem occurs simultaneously with the change in the batch number of the material.

2. Refer to the manufacturer's recommended instructions for various types of laminates. Contact the laminate manufacturer to find out the specific drilling speed, feed, drill and punch temperatures for each grade of laminate. Keep in mind that each manufacturer uses a different mixture of resin and substrate, and the recommendations will vary.

3. Carefully preheat the laminate and be sure to find any overheated areas, such as the overheated area under the heat lamp. When heating materials, the principle of first in, first out should be observed.

4. Test with the laminate manufacturer to obtain aging characteristics data for the material. Turnover inventory makes the stock usually a newly produced sheet. Be sure to detect any overheating that may occur during storage in the warehouse.

 

4. Warping and distortion problems

It is now a symbol: the substrate is warped or twisted before, during or after processing. The tilt of the hole after soldering is also a sign of warpage and distortion of the substrate.

Inspection method: With the floating welding test, it is possible to carry out the incoming material inspection. The 45 degree tilt soldering test is particularly effective.

possible reason:

1. The material warps or twists at the time of receipt or after sawing and trimming, 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, when placed vertically, are bowed or deformed.

3. The warpage is caused by the unequal coverage of the copper wall foil, which is 1 ounce on one side and 2 ounces on the other side: the plating layers are not equal, or the special printed board design causes copper stress or thermal stress.

4 When the soldering is improper or improper, the heavy components in the soldering operation will also cause warpage.

5. During the process or soldering process, the hole displacement or tilt on the material is caused by improper curing of the laminate or stress of the substrate glass cloth structure.

Solution:

1. Straighten the material or release the stress in the oven, and perform the cutting operation according to the angle of inclination recommended by the laminate manufacturer and the heating temperature of the sheet. Contact the laminate manufacturer to ensure that there are no structurally uneven substrates.

2. Store the material in a cardboard box or lay it flat on the shelf. Usually the material should be placed at an angle of 60 degrees or less to the ground.

3. Contact the laminate manufacturer to avoid unequal copper foil on both sides. Analyze plating and stress, or local stresses caused by heavy components or large copper foil areas. Redesign the printed board to balance the component and copper area. Sometimes most of the wires on one side of the printed board and the other side of the printed circuit are laid vertically, so that the thermal expansion of the two sides is not equal and causes distortion, and such wiring should be avoided whenever possible.

4. In soldering operations, printed boards, especially paper-based printed boards, must be clamped with clamps. In some cases, heavy components must be balanced with special fixtures or with fixtures.

5. Contact the laminate manufacturer for any recommended post-cure measures. In some cases, laminate manufacturers recommend another laminate for use in more stringent or special applications.

 

V. The white or delaminated layer of the laminate

It is now a symbol: white spots or cloth appear on the surface or in the material; it can appear locally or on a large area.

Inspection method: Proper floating welding test.

possible reason:

1. During soldering, large areas of foaming are caused by moisture and volatiles that are pressed into the material. Poor machining is also a cause because the laminate is layered so that the laminate absorbs moisture during the wet process.

2. White cloth or white spots are generated during soldering due to uneven laminate structure, improper laminate curing, poor stress relief of the laminate, or poor copper plateability.

3. Exposure of fibers or severe white spots during soldering operations. This is due to excessive contact with the solvent, particularly a chlorine-containing solvent, which softens the resin.

4. When the substrate is heated, the Titanium or the connecting terminal which is tightly fixed will cause great stress on the sheet. As a result, white spots appear around this dense area. The sheet is immediately stressed during dip soldering or after dip soldering, and the deflection or bending will also whiten.

Solution:

1. Inform the laminate manufacturer to identify a batch of laminates with such problems. The recommended machining method is used for all plates.

2. Contact the laminate manufacturer for instructions on how to release the stress on the printed board prior to dip soldering. When the printed board is stored for a period of time under high humidity, it will absorb excess moisture, which will affect the solderability of the printed board. Pre-baking and preheating the printed board prior to the dip soldering operation to reduce thermal shock will help solve both of these problems (see About Multilayer Materials, Moisture Absorption Data for Stored Printed Circuit Boards).

3. Contact the laminate manufacturer to obtain the optimum solvent and application time. When the substrate is changed, verify all wet processing techniques, especially solvents.

4. In wave soldering or manual soldering operations, loosen the tightened terminal and remove any heat sink or heavy components prior to dip soldering. Verify the correctness of the machining operations, especially the punching operation, to ensure the white point and the slight delamination caused by improper operation. Ensure that the plate is properly clamped with a clamp and is not stressed when heated. Do not quench the printed board by placing it in a cold flux remover while hot or under stress.

 

6. Bond strength problem

It is now a symbol: in the dip soldering process, the pads and wires are detached.

Inspection method: During the inspection of the feed, fully test and carefully control all wet processing processes.

possible reason:

1. The delamination of the pad or wire during processing may be due to plating solution, solvent etch or copper stress during the plating operation.

2. Punching, drilling or perforating will cause the pad portions to detach, which will become apparent during the hole metallization operation.

3. During wave soldering or manual soldering operations, pad or wire detachment is usually caused by improper soldering techniques or excessive temperature. Sometimes the laminate or wire is detached because the laminate is not properly bonded or the thermal peel strength is not high.

4. Sometimes the design wiring of the printed board causes the pads or wires to detach in the same place.

5. During the soldering operation, the retained heat of absorption of the component causes the pad to detach.

Solution:

1. Give the laminate manufacturer a complete list of solvents and solutions, including the processing time and temperature for each step. Analyze whether the plating process has copper stress and excessive thermal shock.

2. Obey the mechanical processing methods of push storage. The metallized holes are often analyzed to control this problem.

3. Most of the pads or wires are disconnected due to the lack of strict requirements for all operators. Failure of the solder bath temperature test or extension of the residence time in the solder bath can also occur. In the manual soldering trimming operation, the pad detachment was probably due to the use of improper wattage of electric ferrochrome and the failure to perform professional process training. Some laminate manufacturers now use laminates that have high levels of peel strength at elevated temperatures for use in stringent soldering.

4. If the detachment caused by the design wiring of the printed board occurs in the same place on each board; then the printed board must be redesigned. Usually, this does happen in thick copper foil or wire corners. Sometimes, such a phenomenon occurs with long wires; this is because of the difference in thermal expansion coefficient.

5. Remove the heavy components from the entire printed board, if possible, or after the dip soldering operation. The soldering iron is usually carefully soldered with a low wattage soldering iron, which is shorter than the component dip soldering.

 

Seven. Various soldering problems

It is now a symbol: there are blast holes in cold solder joints or solder joints.

Inspection method: The hole is often analyzed before and after dip soldering to find out where the copper is stressed. In addition, the raw material is subjected to the feed inspection.

possible reason:

1. The blast hole or cold solder joint is seen after the soldering operation. In many cases, the plating is poor, and then expansion occurs during the soldering operation, causing holes or blast holes in the walls of the metallized holes. If this is produced during the wet processing process, the absorbed volatiles are covered by the coating and then driven out under the heat of dip soldering, which creates a spout or blasthole.

Solution:

1. Try to eliminate copper stress. The expansion of the laminate in the z-axis or thickness direction is generally related to the material. It can cause the metallized holes to break. Advice with laminate manufacturers to obtain materials with less z-axis expansion.

 

        Eight. Oversize change problem

It is now a symbol: the size of the substrate is out of tolerance or misaligned after processing or soldering.

Inspection method: Full quality control during processing.

possible reason:

1. The direction of the texture of the paper-based material is not noticed, and the forward expansion is about half of the transverse direction. Moreover, the substrate cannot be restored to its original size after cooling.

2. If the local stress in the laminate is not released, it sometimes causes irregular dimensional changes during processing.

Solution:

1. The entire production staff often cuts the sheet in the same structural texture direction. If the dimensional change is outside the allowable range, consider using a substrate instead.

2. Contact the laminate manufacturer for advice on how to release material stress prior to processing.

 


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