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How do PCB manufacturers choose lead-free solders
For PCB manufacturers, although lead-free solder has not been widely used in the плата цепи профессия, the variety of patented formula products has long been confusing. и разные бренды не могут сказать, что они могут сказать свои добрые слова, and it makes people like a king who does not know what to do? за короткое время, I want to correctly evaluate the long-term variety of mass production from the results of a few simple experiments. Can
Reliability, people donât know what to do! The following are some recognized guidelines for lead-free solder selection:
âNontoxic of lead-free solder
âThe supply of lead-free solder is indispensable and the price is reasonable (Available and Affordable)
âThe plastic range of lead-free solder should be very narrow. Narrow Plastic Range (refers to tensile strength test)
âThe performance of lead-free solder (Acceptable Wetting)
âThe lead-free solder is a material that can be mass-produced (Material Manufacturable)
âThe manufacturing process temperature of lead-free solder is not too high and can be widely recognized (Acceptable Processing Temperature)
âThe solder joint reliability of lead-free solder is good (Form Reliable Joints)
Generally meet these conditions and can replace the current Sn6три/припой из сплава Pb37. In the past few years,PCB manufacturers have paid more attention to the following formulas:
1. The tin-silver co-fusion gold Sn96.5/Ag3.5 of lead-free solder
The melting point of this two-phase alloy is 221 degree Celsius. It has been used for many years in the ceramic hybrid board industry (Hybrid), Он больше всего пользуется популярностью в новом американском сельскохозяйственном союзе, Ford, Моторола, and Japanese TI and German researchers. Он считается наиболее подходящим припоем для замены СНБ. . Однако, some American industry players believe that the Wetting during the fusion welding process (Ref1ow) is very poor, и трудно добиться идеального качества. This is
Because the surface tension is too high when it is in liquid state, the contact angle (Contact Ang1e) is too large, resulting in insufficient spreading properties (Spreadin g). Однако, удельная электропроводность материала на 30% выше, чем Sn63/Pb37, and the proportion is also lower than 12%. Однако, the coefficient of thermal expansion (CTE) is negatively higher than 20%.
оба, lead-free solder tin and copper co-fusion gold Sn99.3/Cu0.7
The melting point of this two-phase alloy is 227°C. The United States N O r t e 1 believes that its (wave soldering in nitrogen atmosphere) welding quality is almost on par with that of Sn63/Pb37 в телефонной продукции. However, если в нормальном воздухе сварка оловом, not only the wettability will be worse, Но точки сварки также имеют шероховатый и текстурный внешний вид. Moreover, механическая прочность тоже хорошая., and it is almost listed in various categories without
Lead solder is at the bottom of the list. However, due to the low price and the fact that oxidation is not easy to occur in the tin flow, и мало шлака, N E M I of the United States believes that it is suitable for use in tin. когда производители PCB хотят вылить олово, Этот сплав должен быть более подходящим материалом. First
3. безобидный припой/Ag/Cu
The eutectic temperature of this most mainstream three-phase alloy is around 217 degree Celsius (Sn3.5 A g 0.9Cu). There are as many as seven or eight kinds of approximate formulas with different weight ratios. широкий раствора, which is the current PCB The manufacturer recognized the best combined lead-free solder and the most likely general standard solder. The role played by a small amount of copper is:
(1) It can reduce the continuous increase of foreign copper in the solder joints.
(2) It can lower the melting point of solder.
(3) It can improve tin wetting, усиление выносливости точки сварки и термическое сопротивление усталости на предыдущей стадии.
There are more than 100 kinds of lead-free solder alloys in the literature. независимо от свариваемости, Сопоставление прочности и цены точек сварки, any of them is much inferior to the current Sn63. оценка и рассмотрение условий, it seems that the "three-phase eutectic of tin, в различных гнилых яблоках "серебро и медь" все еще немного лучше. Сегодня он стал самым любимым во всех трех областях Европы, America and Japan.
На рисунке 2 ниже сопоставляются пять видов бессвинцовых припой на поверхности облицовки без свинца.
5. олово, silver, bismuth and other metals, четвёртый сплав - олово./Ag/полностью/X
When bismuth is added to this alloy solder, понижение точки плавления, свариваемость улучшится, and the solderability is almost the best among all lead-free solders. However, the trouble of "bismuth cracking" is prone to occur. нсмс также заявляет, что при сварке на гребне волны материалы, содержащие Висмут, могут быть легко "трещины в олове через кольцо сквозного отверстия", Но это по - прежнему выбор японского производителя.
Of course, a large number of PCB manufacturers have to consider the cost of solder.
