PCB Production Process Substrate and laminates may happen some quality Question

It is impossible to manufacture any number of printed circuit boards without running into some problems, part of which is due to the material of the copper-clad laminate. When quality problems occur in the actual manufacturing process, it is often the substrate material that is the cause of the problem. Even a carefully written and implemented technical specification for laminates does not specify the testing required to determine that the laminates are the cause of a manufacturing process problem. Here is a list of some of the most common laminate problems encountered and how to identify them. Whenever a laminate problem is encountered, consideration should be given to adding it to the laminated material specification. Often, if this specification is not fleshed out, it will result in continual quality changes that will result in product obsolescence. Usually, material problems due to variation in laminate quality occur in products manufactured with different batches of raw materials used by the manufacturer or with different pressing loads. Very few users have enough records to be able to identify a particular pressing load or material lot at a PCB processing site. As is often the case, printed circuit boards are constantly being produced and loaded with components, and warp continuously in the solder tank, wasting a lot of labor and expensive components. If the loading batch number is immediately available, the laminate manufacturer can check the resin batch number, copper foil batch number, curing period, etc. In other words, if the user does not provide continuity with the laminate manufacturer’s quality control system, then the user itself will suffer in the long term. The following are some general issues related to substrate materials in the manufacture of printed circuit boards.

一, surface problems
Signs: poor adhesion of the print, poor adhesion of the coating, failure to etch off certain parts, and failure to solder certain parts.
The inspection method can be used: usually with water on the surface of the plate to form visible water lines for visual inspection, or with ultraviolet lamp irradiation inspection, with ultraviolet lamp irradiation of copper foil can be found in the copper foil resin.
二. Appearance problem
Signs: the color of the laminate is obviously different, the surface color is different, the surface or the inner layer is stained, the laminate surface has a variety of color thin layer
Available inspection method: visual.
Possible reasons:
1. There are white cloth lines or white spots on the surface of the glass cloth base pressing plate before PCB processing or after etching.
2. After PCB processing, more white spots or exposed glass cloth appear on the surface.
3. After processed by process PCB, especially after soldering, there is a thin layer of white film on the surface, which indicates that the resin is slightly etched or has foreign deposition.
4. The color variation of the substrate exceeds the possible acceptable appearance requirements.
5. Because the laminate is overheated or soaked for a long time by high concentration of some potions, the appearance of the substrate produces brown or brown markings.
Mechanical PCB processing problems
Signs: Inconsistent quality of punching, shearing and drilling PCB, poor adhesion of coating or uneven coating in metallization holes.
Inspection method: check incoming materials, test various key mechanical PCB processing operations, and the laminate incoming materials through the hole metallization process, routine analysis.
.
Warpage and distortion problems
Signs: Before, after or during PCB machining, the substrate warps or warps. The tilt of the solder hole is also a sign of warping and distortion of the substrate.

Appearance problem  

Signs: the color of the laminate is obviously different, the surface color is different, the surface or the inner layer is stained, the laminate surface has a variety of color thin layer

Available inspection method: visual.

Possible reasons:

1. There are white cloth lines or white spots on the surface of the glass cloth base pressing plate before PCB processing or after etching.
2. After PCB processing, more white spots or exposed glass cloth appear on the surface.
3. After processed by process PCB, especially after soldering, there is a thin layer of white film on the surface, which indicates that the resin is slightly etched or has foreign deposition.
4. The color variation of the substrate exceeds the possible acceptable appearance requirements.
5. Because the laminate is overheated or soaked for a long time by high concentration of some potions, the appearance of the substrate produces brown or brown markings.

 

Mechanical PCB processing problems  

Signs: Inconsistent quality of punching, shearing and drilling PCB, poor adhesion of coating or uneven coating in metallization holes.

Inspection method: check incoming materials, test various key mechanical PCB processing operations, and the laminate incoming materials through the hole metallization process, routine analysis.

.

Warpage and distortion problems

Signs: Before, after or during PCB machining, the substrate warps or warps.  The tilt of the solder hole is also a sign of warping and distortion of the substrate.

Inspection method: float welding test is used. Incoming material inspection is possible.  The 45 degree tilt soldering test was particularly effective.

 

五.Laminate white spots or layers  

Signs: The appearance of white spots or markings on surfaces or materials;  Can appear locally, also can appear on the large area.

Inspection method: proper float welding test.

Possible reasons:

 

Adhesion strength problem  

Symptoms: Pad disconnects from wire during a dip soldering operation.

Inspection method: fully test and carefully control all wet PCB machining processes during incoming inspection.

Possible reasons:

1. Pad or wire detachment during PCB machining may be caused by electroplating solution, solvent etching or copper stress during electroplating operation.
2. Punching, drilling or perforation can cause partial disintegration of pads, which will become apparent during hole metallization operations.
3. During wave soldering or manual soldering operations, pad or wire detachment is usually caused by improper soldering technique or excessive temperature.  Sometimes because the original laminate bonding is not good or the thermal peeling strength is not high, resulting in the pad or wire detachment.
4. Sometimes PCB design wiring will cause pads or conductors to detach in the same place.
5. Retained absorbed heat from components during soldering operations may cause pad detachment.

 

All kinds of soldering problems  

Symptoms: cold solder or tin solder with burst holes.

Inspection method: before and after the dip soldering, the hole is often analyzed to find the copper stress, in addition, the raw material to carry out incoming inspection.

Possible reasons:

1. Blast holes or cold soldering spots are seen after soldering operations.  In many cases, poor plating is followed by expansion during the soldering operation, resulting in cavities or burst holes in the metallized hole walls.  If this is produced during the wet PCB processing process, the absorbed volatiles are covered by the coating and then driven out by the heating of the dip solder, this will produce a nozzle or burst hole.

Solutions:

1. Try to eliminate copper stress.  The expansion of laminates in the z axis or thickness direction is usually material dependent.  It can cause the metallized hole to fracture.  Work with the laminate manufacturer for advice on materials with low Z-axis expansion.

Excessive size change problem

Signs: out of tolerance or out of alignment after PCB machining or soldering.

Inspection method: fully carry out quality control in the process of PCB processing.

Possible reasons:

1. No attention was paid to the direction of structural texture of paper-based materials, and the forward expansion was about half of the transverse expansion.  And the substrate does not return to its original size when it cools.
2. If the local stress in the laminate is not released, it will sometimes cause irregular size changes during the PCB machining process.