咨詢熱線:

0755-26690898

FAQ

Tin beads causes and countermeasures
Solder balling is one of the major defects in the surface mount process, its production is a complex process, but also the most annoying problem to completely eliminate it, it is very difficult.
In general, the causes of the solder beads is multifaceted and comprehensive. Group of the thickness of the solder paste printing, paste
Into and the degree of oxidation, the production of the template, and openings, solder paste whether the absorbed moisture, the component placement pressure, components and pads weldability, reflow soldering temperature settings, the influence of the external environment may be solder beads generated reasons.

The selection of the solder paste directly affect the quality of welding. The metal content in the solder paste, the degree of oxidation of the solder paste, the granularity of the alloy of the solder powder in the solder paste and solder paste printing to a thickness of the printed board can affect the generation of the weld bead.
A solder paste of metal content. The metal content of the solder paste the mass ratio of approximately 89% to 91.5% when the metal content increases, the increase in the viscosity of the solder paste, can effectively resist the the vaporization force generated in the preheating process. Further, the increase of the metal content, the metal powder arranged closely to make it more easily combined without being blown off when melted. Furthermore, the increase of the metal content is also possible to reduce the "slump" of the solder paste printing, therefore, difficult to produce the solder beads.
B, the solder paste is a metal oxide degrees. In the solder paste, the higher the metal oxidation degree in the welding metal powder combined greater the resistance, the less infiltration paste pads and between components, leading to a reduced weldability.
C, in the solder paste of the metal powder particle size. The smaller the particle size of the powder in the solder paste, the greater the overall surface area of ??the solder paste, resulting in a higher degree of oxidation of the fine powder, and thus the solder beads phenomenon is exacerbated. Our experiments show that: the selection of the finer particles of solder paste, solder beads easier.
D, the thickness of solder paste on the printed circuit board printing. The thickness of the solder paste printing is an important parameter of the printing of the drain board, typically between 0.12mm-0.20mm. Solder paste is too thick will cause the solder paste slump ", to promote the generation of solder beads.

2, solder paste dry analysis
Solder paste viscosity rise in the use of the process, even the hair shaft will lead to many problems, such as poorly printed, the decrease in the amount of leakage and India, under the tin devices shift slapper, will lead to the welding yield dropped. Many possible factors that cause the solder paste dry, can be broadly summarized Conditions of Use reasons and solder paste quality reasons, but in essence, are due to the chemical reaction flux and tin powder caused.


A. Conditions of use
Warmed extend shelf time: in order to slow down the speed of response of the flux and tin powder, solder paste usually need cold storage. Before using solder paste must be at room temperature to warm. Generally a 500g mounted solder paste must be at least warm for more than two hours, so that the same temperature and the ambient temperature of the solder paste and the Prohibition of the Use. The return temperature is less than the open sealed lids will cause moisture in the air because of the temperature difference to condense and into the solder paste, causing the hair shaft.
Also need to be reminded that if the use of solder paste mixer, it should automatically shorten or cancel the return temperature process. Automatic mixers generally use centrifugal design, high-speed rotation causes the solder paste temperature rise (increase depends on the mixing time).


Ambient temperature and humidity: recommended ambient temperature of 20-25 ℃, relative humidity of 30% -60%. High temperature reaction rate will accelerate the evaporation rate of the solvent in the solder paste and solder paste flux and tin powder (usually the temperature is increased by 10 ℃, approximately doubling the speed of a chemical reaction), therefore the solder paste is easier dry; temperature is too The low will affect the viscosity and rheology of the solder paste, prone to printing defects. Similarly, the humidity is too high water vapor into the solder paste greatly increased; too low humidity will accelerate the rate of evaporation of the solvent in the solder paste.

Two. Solder paste quality
The solder paste quality problems is the most important reason causing dry. The quality problems referred to here is not a supplier production control problems caused by fluctuations in the quality (in fact rarely triggered by such fluctuations dry), but rather refers to the instability caused by design flaws in the solder paste itself.
Solder paste is a mixture of tin powder and flux, so the quality of the tin powder and flux stability will affect the life of solder paste, flux stability is a key factor to decide whether the solder paste is easy to dry.
So-called flux stability is more stable at room temperature, their physical and chemical properties, not easy crystallization or react with the metal. Is well known, the main role of the flux is to remove oxides on the surface of the solder and the base material, which is a chemical reaction process. Flux to be played this role must have activity flux activity system welding can be carried out smoothly, the activity, the stronger the ability to remove oxides, otherwise weak. In the storage and use of the process due to active solder paste, flux and tin powder reaction there is always only in the low temperature reaction rate is very slow, soldering temperature quickly. Therefore, the reaction speed determines the service life of the solder paste flux and tin powder room temperature.
Rational design of solder paste flux activity must meet two conditions, with strong activity to complete the welding soldering temperature, both at room temperature while maintaining inert. In order to achieve this purpose, it is necessary to perform special processing to the active group, so that it does not show activity at room temperature, when the temperature rises to a certain extent, can quickly release the active. Prone dry paste tend to the reactive groups in the active system at room temperature, is more active, Therefore, at the time of printing, with the intervention of the water vapor and oxygen, to accelerate the speed of reaction of the flux with tin powder, causing dry.
Third Conclusion
Paste in the process of storage and use, there is always a chemical reaction. Although this reaction is inevitable, but the rational design of solder paste should be quite slow reaction speed under normal conditions of use, its service life is sufficient to meet normal production needs. The solder paste is often prone to dry due to the recipe design flaws caused. In addition, to ensure that the use of the environment and meet the requirements of the specification operation prolong the solder paste life. Other factors, such as solvents in the use of volatile also on the useful life impact, but it is not a major factor.

版權所有 Copyright ? 深圳市福英達工業技術有限公司 總機:0755-26690898/26695796 傳真:0755-26820233
地址:深圳市寶安區松崗鎮松崗東路6號8棟 電子信箱:szfitech@sohu.com
服務時間:周一至周五,上午8:30-12:00;下午13:00-17:00(節假日正常休息) 技術支持:
var _hmt = _hmt || []; (function() { var hm = document.createElement("script"); hm.src = "https://hm.baidu.com/hm.js?44d5929b98ed1fd093ffc3d47ec712b9"; var s = document.getElementsByTagName("script")[0]; s.parentNode.insertBefore(hm, s); })(); document.writeln("");