tailieunhanh - SMT Soldering Handbook surface mount technology 2nd phần 9

trừ khi buộc phải làm như vậy. 4. Các tiêu chuẩn wavesoldering nhiệt độ 250 ° C/480 ° F cộng thêm hoặc trừ đi một vài độ, giống như góc tải, kết quả của hơn bốn thập kỷ kinh nghiệm wavesoldering thực tế. Nếu không có một nhu cầu hấp dẫn, nó được khuyến khích không để khởi hành từ. | 294 Cleaning after soldering To speak of an ozone layer is therefore not quite accurate but in the public mind the term has created a powerful image of its concrete existence and of the threat to it thus the term serves a useful purpose. The ozone layer s crucial importance for life upon earth is its function as a powerful filter for UV radiation below the wavelength of 320 m. Radiation within that range has many different effects on humans animals plants and also man-made materials. Most of them are harmful and some of the damage that can be caused will be discussed presently. Ozone owes its presence in the stratosphere to a delicate balance between the processes of its formation and of its depletion. Ozone is formed from oxygen present in the stratosphere through a photochemical reaction under the influence of the intense UV radiation which prevails at those heights. Its depletion is due to a breakdown of two ozone molecules into three oxygen molecules through a series of steps initiated by the catalytic effect of certain free radicals like Cl or NO which are naturally present in the stratosphere. These free radicals have diffused upwards as products of naturally occurring processes down at ground level such as the decomposition of organic matter. The arrival in the stratosphere of additional amounts of man-made free radicals like Cl NO and also Br has now tipped the balance towards the decomposition of ozone. Measurable overall depletion has set in. It is particularly severe in the Arctic regions and especially in the Antarctic where the ozone layer periodically disappears completely ozone hole . In the latitude of the UK too the ozone loss since 1969 has been estimated at approximately 7 .1241 By now public awareness of the ozone problem has risen to a level where ozone figures are given in the daily press. The situation is aggravated by the catalytic nature of the depletion process which means that the offending radicals remain in the stratosphere for a long .