Application of the most fire cleaning free welding

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Application of cleaning free welding technology

Abstract: cleaning free welding technology is a practical technology widely used in the electronic assembly industry at present, which has the advantages of simplifying the process flow and saving manufacturing costs. The author has the honor to preside over the introduction, evaluation, promotion and implementation of Shanghai Bell's cleaning free welding technology, which has been more than five years. In the process of evaluation and implementation, I have a certain understanding and accumulation of practical application. I take this opportunity to write some experiences to discuss with you, which is really a good idea. Please correct any mistakes

key words: promotion and implementation of cleaning free welding evaluation and testing

Part I: preface

at the turn of the century, history is about to turn a new page; For the communication electronics industry, it is full of opportunities and challenges. Summing up the past, basing ourselves on the present and creating the future is the biggest topic for each professional and technical personnel at present. Looking back on the past decade, the widespread promotion of no clean soldering process has formed a beautiful scenic spot in the electronic assembly industry at the end of the 20th century

Part II: what is cleaning free welding technology?

the cleaning free process is an advanced technology based on the original traditional cleaning process, which simplifies the process flow on the basis of ensuring the original quality requirements, rather than a simple "no cleaning" - it is only adopted for the characteristics of some low-end consumer products that do not require high quality reliability, although the cleaning link is omitted, It is based on the relatively low quality

CFC CFC products and 1.1.1-trichloroethane have been used as cleaning agents in traditional cleaning processes for post welding cleaning of assembly plates (pbas) to remove residual conductive substances or other pollutants on the surface of pbas and ensure the long-term reliability of products. However, CFC and other cleaning agents contain ODS ozone depleting raw materials, which destroy the ecological environment and seriously threaten human safety. Therefore, the "Montreal agreement" signed in 1987 and the "Copenhagen Conference" and "Brussels Conference" held successively clearly stipulate that the use of ODS cleaning agents will be completely prohibited in a relatively short period of time. It can be seen that it is imperative to adopt advanced technology to replace the original cleaning process

At the end of 1980s, technicians in advanced countries successively developed four main alternative technologies for the electronic assembly industry, including non CFC solvent cleaning/semi water cleaning/water cleaning and non cleaning technologies. From the perspective of manufacturing and process management, cleaning free welding technology undoubtedly has incomparable advantages. It has the characteristics of shortening production cycle, reducing waste production, reducing raw material consumption, and reducing equipment maintenance frequency, which saves production costs to a great extent

non cleaning welding technology includes non cleaning wave soldering technology and non cleaning reflow soldering technology. The former is developed from the traditional wave soldering technology, and achieves the cleaning free effect through the reform of equipment and materials, mainly solving the wave soldering of through-hole components and solidified surface components in the hybrid assembly technology. The latter is an important process link in surface component assembly, which is more popular in China at present. Through material selection and process control to achieve the cleaning free effect, it mainly solves the reflow soldering of surface mount components

Part III: evaluation of cleaning free effect and product reliability

when using cleaning free welding technology in practice, it is easy to ask such a question: "how clean is clean?" “How clean is clean enough?” That is, how to evaluate the effect of cleaning free. This is the most fundamental problem in the cleaning free welding technology, which plays a decisive role in the practical promotion and implementation of the new process

the application of new technology has replaced the original cleaning technology; Then, is the original product reliability evaluation standard system still applicable to cleaning free welding technology? The following analysis can help solve the problem

under the original branch conditions, the process evaluation and test system includes:

1. Ionic contaminant test ion concentration test

use rose (resistance of solvent extract) test method, that is, pollutant extract test method, and use special instruments (such as omega me ter) to automatically count the content of conductive ion pollutants contained in the extract, And judge whether it meets the relevant standards (such as the cleanliness standard of < g NaCl/in^2 specified in mil-p-28809) and meets the requirements of product reliability; Mainly for the testing of rosin based materials. However, the test itself has three major defects:

(1) it cannot distinguish the types of pollutants, so it is impossible to determine the impact of some pollutants on product characteristics; (2) The extraction liquid cannot exclude all ionic pollutants into the total, especially for some SMT components with complex pin structure, which will affect the final judgment result

(3) it cannot detect non conductive pollutants, such as liquids used in HASL (hot air leveling) process; Past practice has proved that these non-ionic pollutants also seriously endanger the reliability of products

2.sir (surface insulation resistance) test surface insulation resistance test (the specific content will be introduced below, omitted here)

the above facts show that in the face of the arrival of new technologies and new materials, we must develop new process evaluation methods and test criteria to meet new challenges. At present, our new system mainly includes the following three contents:

1) ionic/organic cleanliness test cleanliness test

different from the original ion concentration test, the cleanliness test introduces chromatographic analysis methods, including IC (ion chromatography) ion chromatography and HPLC (high pressure liquid chromatography) high pressure liquid chromatography, Features:

A. It can help define the types of pollutants and determine the quantity and level of pollutants contained on the surface of components and light plates

b. it is a laboratory means and has not yet become a direct production support tool

c. it can be used to determine the process lower limit of materials and provide relevant links with existing testing methods

by marking the quantity level of ionic/no ionic substances and referring to the existing acceptable condition technology, the correlation with Sir and ESS tests can be determined; Through comparison, it can help us find the on-site process control methods and monitoring tools suitable for the actual production, so as to effectively ensure the effective implementation and control of the cleaning free welding technology

2) Sir test reliability swab

this is a means to simulate the long-term reliability impact of harsh environmental factors on products in a short term by artificially applying high temperature, high humidity and voltage, so as to determine that non yielding is the inherent performance of materials and the implementation effect of cleaning welding process. At present, ipc-sf-818 standard is generally used as the test method and criterion, that is, the reliability requirements must be met only when the specified surface insulation resistance (> 10^8ohm) is reached under the conditions of 85 (c) high temperature, 85% RH relative humidity, 100VDC test voltage and so on. Usually, sir test is carried out together with other chemical analysis methods, so that the evaluator can obtain the evaluation and inspection results as soon as possible and directly. Sir test results used to rely on the skills of operators to a large extent, but with the development of technology and the continuous efforts of various research institutions, sir has gradually become an accurate testing tool and means, which is mainly used to evaluate the impact of residues generated after welding of products such as flux, cleaner, SolderPaste and soldermask on product reliability

3) ess (electrical stress screening) test

this method is mainly used to evaluate the reliability of functional products. It combines various environmental factors such as temperature/humidity/vibration to simulate extreme environmental damage; At the same time, functional tests are carried out and compared in each stage before/during/after the test to determine the reliability of the product. According to user requirements, ESS can include a series of test methods, such as strong temperature cycle test, humidity tendency test, thermal shock test and dew point test. Its characteristics are: the test is rapid, and the swab results can be obtained as soon as possible; It can more truly reflect the impact of the environment on product reliability. The disadvantage is that the finished product is required as the test object every time, and the cost is high. In any case, ESS means will more accurately show the inevitable link between cleaning free welding technology and long-term reliability

through the process evaluation system formed by the above test items, we are fully capable of answering questions such as "what is cleaning in the end" and "what kind of cleaning is enough cleaning". With such a system guarantee, we can clearly make an accurate analysis and positioning of the implementation and control of the whole process, and the cleaning free welding process can truly show its unique charm to the world

Part IV: implementation of cleaning free welding process

after clarifying the test and evaluation criteria, the next thing to consider is how to promote and implement this new technology to give full play to its due benefits. Compared with the original cleaning technology, its advantages are obvious; However, it is a brand-new process technology after all. People who are used to the old model and even your boss may not be easy to accept it. They often ask some questions: "will this process procedure more reliable assemblies a with the large use of carbon fiber composites in aircraft, nd cost less than my current process?" In other words, what kind of impact can the implementation of this new process bring to enterprises and manufacturing technology. As we mentioned earlier, the cleaning free welding technology has the characteristics of reducing production costs and ensuring product quality. After demonstrating its feasibility in theory, what is it actually like? The only way to answer the above questions is to promote the implementation, and test it with the method of practice. As we know, "practice produces true knowledge"

in fact, the key to popularizing this new process is to completely change people's understanding of welding process; Through the cooperation between departments, mastering the ability to solve practical problems and carefully selecting what materials and equipment to use are indispensable and important in the implementation process

the first point: strengthen departmental cooperation, and set up a special process promotion and implementation team together with process, quality, materials and production personnel. Such a combination has the following functions:

* each performs its own duties and has a strong driving force not only to carry out basic research

* multi viewpoint observation is conducive to early detection of various hidden dangers

* we can exchange what we need, unify our understanding in solving problems, and enhance the efficiency of solving practical problems

its workflow can be divided into the following steps:

1. Definition: consider various possible factors, formulate action objectives and evaluation standards

2. Evaluation: formulate an evaluation plan, guide the test process, and analyze the results

3. decision: determine candidates according to test results and document requirements, and then purchase equipment and prepare for acceptance test

4. implementation and promotion: install the machine, adjust the process, solve practical problems, and finally put it into batch use

second key point: master the connotation of non cleaning technology and improve the ability to solve practical problems. On the one hand, process engineers must study and study the cleaning free welding technology in depth and in detail

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