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PCB Tech

PCB Tech

Analysis of the Causes of Wrinkles and Bubbles in the Soldering Inks of Multilayer Circuit Boards
2021-08-24
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Author:Aure

Analysis of the Causes of Wrinkles and Bubbles in the Soldering Inks of Multilayer Circuit Boards

   1. Multi-layer circuit board The blistering of the board surface is actually a problem of poor bonding of the board, that is, the surface quality of the board, which contains two aspects:
 
   1. The surface cleanliness of multilayer circuit boards;
 
   2. The problem of surface micro-roughness (or surface energy). The blistering problems on the PCB surface of all circuit boards can be summarized as the above-mentioned reasons. The bonding force between the plating layers is poor or too low, and it is difficult to resist the plating layer stress, mechanical stress and thermal stress generated during the production and processing of the circuit board in the subsequent production process and assembly process, resulting in different degrees of separation between the plating layers.
 
   2. Some factors that may cause poor board quality in the production process are summarized as follows:
 
  1. The problem of substrate processing: Especially for some thin substrates (generally below 0.8mm), because the substrate has poor rigidity, it is not suitable to use a brushing machine to brush the board. This may not be able to effectively remove the protective layer specially treated to prevent the oxidation of the copper foil on the PCB surface during the production and processing of the substrate. Although the layer is thin and the brush is easier to remove, it is difficult to use chemical treatment. It is important to pay attention to control during production and processing, so as to avoid the problem of blistering on the surface caused by poor bonding between the copper foil and chemical copper on the surface of the multilayer circuit board; this problem will also occur when the thin inner layer is blackened. There are problems such as poor blackening and browning, uneven color, and partial blacking and browning.


Multi-layer circuit board ,processing of the circuit board ,PCB multi-layer circuit board

2. Multi-layer circuit board  The surface of the board is in the process of machining (drilling, lamination, milling, etc.) caused by oil or other liquids contaminated with dust and pollution. Poor surface treatment. .
 
3. Poor sinking copper brush plate: the pressure of the sinking copper front grinding plate is too large, causing the hole to be deformed, brushing the hole copper foil rounded corners or even the hole leaking the substrate, which will cause the sinking copper plating spray tin welding process Foaming phenomenon at the orifice; even if the brush plate does not cause leakage of the substrate, the excessively heavy brush plate will increase the roughness of the orifice copper, so the copper foil at this place is likely to be over-roughened during the micro-etching roughening process , There will also be certain quality hidden dangers; therefore, it is necessary to strengthen the control of the brushing process, and the brushing process parameters can be adjusted to the best through the wear scar test and the water film test;
 
4. Water washing problem: The electroplating treatment of copper deposits has to undergo a lot of chemical treatments. There are many chemical solvents such as acid and alkali, non-polar organic, etc., and the surface of multi-layer circuit boards can not be washed with water. It will cause cross-contamination, and it will also cause poor local processing or poor processing effects on the surface of the PCB multi-layer circuit board, uneven defects, and some bonding strength Therefore, it is necessary to pay attention to strengthening the control of washing, mainly including the control of washing water flow, water quality, washing time and plate dripping time; especially in winter, the temperature is lower, the washing effect will be greatly reduced, and more attention should be paid to Strong control of water washing;
 
5. Micro-etching in the pre-treatment of copper sinking and the pre-treatment of pattern plating: Excessive micro-etching will cause the hole to leak the base material and cause blistering around the orifice; insufficient micro-etching will also cause insufficient bonding force and cause blistering. ; Therefore, it is necessary to strengthen the control of micro-etching; generally the depth of micro-etching before copper sinking is 1.5-2 microns, and the micro-etching before pattern electroplating is 0.3--1 microns. If possible, it is best to pass chemical analysis and simple The test weighing method controls the micro-etching thickness or the etching rate; in general, the surface of the multi-layer circuit board after the micro-etching is bright, uniform pink, without reflection; if the color is not uniform, or there is reflection, it means that the pre-processing exists Hidden quality hazards; pay attention to strengthen the inspection; in addition, the copper content of the micro-etching tank, the temperature of the bath, the load amount, and the content of the micro-etching agent are all items to be paid attention to;
 
6. Poor rework of copper sinking: some copper sinking or reworked boards after the graphics are transferred during the rework process due to poor fading, incorrect rework methods, improper control of the micro-etching time during the rework process, etc., or other reasons, etc., will cause the PCB board surface to blisters; Rework of copper-immersed circuit boards, if you find bad copper-immersed on the line, you can directly remove the oil from the line after washing with water, and then directly rework without corrosion after pickling; it is best not to re-degrease and micro-etch; for the boards that have been thickened by electricity , The micro-etching tank should be deplated now, pay attention to the time control, you can use one or two plates to roughly measure the deplating time to ensure the deplating effect; after the deplating is completed, apply a set of soft brushes and then press The normal production process is to sink copper, but the corrosion time should be halved or adjusted if necessary.