Second, solder mask.
1.The earliest solder mask in the history of PCB in China.
As early as June 1964, the National Printed Circuit Technology Exchange Conference was held in Beijing 15 Institute (formerly known as Jingzi 115 troops), and the participants in this conference are all research institutes affiliated to the National Defense Science and Technology Commission and the relevant factories of the former Fourth Machinery Department, and I was honored to represent the 761 factory to participate in this conference, one of which is to introduce and demonstrate the manufacturing and application process of solder mask by 15 institutes.
1) Technological process.
The manufacture of solder mask film (a kind of high-temperature resistant soft paper) first punches the high-temperature resistant soft paper according to the position of the original pad, and the hole diameter is larger than the pad 20mm (because the original printed board pad is about 3). Cleaning of the board surface. Brush the punched soft paper (solder mask) and align the pad on the board surface to expose the pad. Brush with alcohol rosin flux. Immersion tin: clamp both sides of the plate surface with a special fixture, in order to avoid the generation of tin beads and burrs, the plate surface passes through the tin surface and then returns in reverse with an S-shaped stroke. Clean the board surface with ethanol and remove the soft paper and clean it again, in fact, now it seems that this is just the immersion tin of the pad, if the component is inserted, it will be dip soldering.
2) Some arguments about solder mask at the time.
In the group discussion at this meeting, there was a debate about whether the surface of the circuit board should be soldered off, because at that time they were all separate components and large volumes, while semiconductor transistors were just sprouting and were all soldered by hand, and one view was that solder masks were not needed; Another point of view is that solder mask ...... must be considered from a development perspective
Also in 1964, visited the downed American unmanned high-altitude reconnaissance plane, the residual nucleus in the part of the circuit board of the instrument did not have solder mask, and later after careful observation, the instrument was manufactured in 1961, until 1965 at a foreign exhibition held by the Beijing Exhibition Center, the circuit board in the electronic equipment on display, are coated with solder mask, and with the development of the whole electronic machine are aware of the importance of circuit board solder mask. That was the end of the controversy.
2.Thermoset solder-resistant.
1) the early application of solder mask: into the late sixties semiconductor technology has begun to popularize, PCB industry experts, masters of the manufacture of solder mask ink for several times of trial production, after all, is not a professional manufacturer of ink, the difficulty is greater, later some enterprises to find resin ink substitutes, are not ideal, then the double resistance of thermosetting solder-resistant into our country, at the beginning of only a few research institutes used, with the increase in consumption, European and American brands through Hong Kong, the most popular at that time The most popular model was the PC-401 series, and later there were a variety of patterns, with a cloth pattern (still in use) and a matte wrinkled type on the surface. At the beginning of the 80s, the national brand and ES-3 were born in Guangdong Institute of Chemical Industry, and after entering the market, it was praised by users for its economy and practicality.
3.Screen printing UV light solid soldering resistance.
When the manufacturing trend of television, video recorder and tape recorder came, thermosetting solder mask is not suitable for these cardboard substrates, with the entry of the whole production line and the introduction of several circuit board manufacturing lines, UV light solid solder mask ink and equipment also hitchhiked into our country. In a very short period of time, whether large or small factories, the use of UV welding technology is very proficient - into the popularization stage, in addition to hitchhiking into China's brand, Europe also entered at the fastest speed, and soon, national and domestic brands have also joined the ranks of competition.
4.Photoimaging solder mask inks.
With the increase of circuit board lines and pad density and the tendency of lines to become thinner and pads to become smaller, the resolution of the original screen printing (thermosetting or UV light solid) solder mask pattern can not reach the accuracy of the pattern, even if the master of screen making and the master of screen printing can not meet the requirements.
Therefore, DuPont launched a solder mask dry film and a special vacuum film machine, but due to the high investment and cumbersome operation and with the continuous development of PCB technology, the solder mask dry film has slowly disappeared. About in the mid-eighties of the last century, a new process, optical imaging solder mask ink into China, both from the thermal shock resistance, resolution, dielectric strength, appearance to meet the requirements of high-density printed circuits, like the aforementioned thermosetting solder mask ink.
At the beginning of the use of some large enterprises and research institutes, and then gradually pushed away, to see the needs of the market, the ink importer actually raised the first to 650 yuan kg (RMB), with the "strange goods" and "no semicolon" attitude appeared in the market, with the European and other regions of the brand and the birth of the domestic nation, domestic brands, began to fall back and steady, with the popularization of this technology ink merchants and merchants to take a pragmatic attitude, but also with the circuit board has been declining.
3. Conductive ink (slurry).
In some places, it is called conductive ink, black conductive oil, carbon oil, and in the United States, it is called conductive polymer. In the conductive paste, the main guide electrosilver paste, conductive copper paste, conductive carbon paste, the main components of which are made of resin and metal powder research and mixing, the above three conductive pastes are used in a number of products according to different conditions.
1.Application range of conductive paste: :
Conductive pastes are widely used, mainly used in the manufacture of connecting wires, jumpers, vias, capacitors, embedded resistors, resistors, heating films, thin film circuits, thin film switches, thin film panels, etc.
1) Application status of conductive carbon paste:
The printed board made of carbon paste is called carbon oil plate or carbon film board, mainly with remote control, ** machine, toys, calculators, because there is only a copper foil wire on one side, and the back is a carbon paste to make the pattern, in the middle of the carbon paste, copper paste or silver paste through the hole to make both sides conductive, so some people call it a false double-sided board, if the surface is blocked by an insulating paste, the surface is printed again carbon paste wire can also form a single-sided double-layer or three-layer board, and can also be made into unequal resistance values in the manufacture of conductive carbon paste, At present, 15 institutes have sold PCBs with embedded resistors in batches and obtained the approval of users (this technology is very common in developed countries), in addition to the rearview mirror of automobiles, and other heating fields have also used carbon paste as the principle of increasing resistance to generate heat, and have made heating films used in different industries.
2) Through-hole and its economy and environmental protection:
After entering the 21st century, the circuit board industry has also given new concepts and application categories to conductive pastes. The through-hole mentioned above refers to the through-hole of the single-sided double-layer board, and here we want to talk about the ordinary FR-4, with a thickness of 16mm~ 2.0mm circuit board through hole, although the vertical and horizontal ratio is larger, but developed countries from the environmental protection and economic interests of considerations, has been used for a large number of products, last year I met a PCB manufacturer in the Pearl River Delta region to receive the order in the double-sided side, with the method of through the hole to complete. In addition, several factories have introduced through-hole equipment in complete sets, which is for economic and environmental considerations. It seems that in the future, the double-sided through hole will be completed with a through-hole, which will account for a certain proportion.
3) Thin-film circuits, switches and panels: Circuits completed by printing patterns with conductive paste on the surface of PI or PET are thin-film circuits, thin-film switches or thin-film panels. For example, the keyboard board of the computer is completely completed by printing wires with conductive silver paste, while in the membrane switch or panel, most of them are printed with single-sided flex boards, jumpers, contacts or graphics completely on the PI or PET film, and the surface is printed with decorative ink.
2.The status quo of conductive paste: the conductive carbon paste used for ordinary carbon film plates, most of them are low-grade products, domestic brands have fully met the requirements of users, and some carbon film plate manufacturers not only manufacture carbon film plates, but also sell them in addition to making their own conductive carbon paste to meet their own use.
Some professional ink manufacturers produce conductive paste, high-grade products are less, mainly in the resistance value of the change rate is larger (of course, also related to the application conditions), and high-grade slurry are monopolized by developed countries in the Americas, Europe and Asia, and recently a domestic brand squeezed into the ranks of competition, the momentum is greater and has a certain amount of customers and a certain sales; In some joint ventures and foreign wholly-owned enterprises in China, the conductive pastes used are imported (foreign designated brands) It is difficult for domestic ink manufacturers to enter, although the storage of these materials is more cumbersome, such as a certain number of foreign brands, cold angelica is required, and users say that they are used to it, which is in sharp contrast to the brands in North America and Europe. In recent years, both imported brands (except for Angelica delica) and domestic brands are developing towards low-temperature curing (referring to general slurry), such as 90C curing slurry which not only saves energy but also accelerates the production cycle.
With the popularization of through-hole technology, as well as the requirements of high quality and environmental protection, there will be a better and larger market for conductive pastes in the future.