Analysis of Printing Red Glue Technology
We are a big printing company in Shenzhen China . We offer all book publications, hardcover book printing, papercover book printing, hardcover notebook, sprial book printing, saddle stiching book printing, booklet printing,packaging box, calendars, all kinds of PVC, product brochures, notes, Children's book, stickers, all kinds of special paper color printing products, game cardand so on.
For more information please visit
http://www.joyful-printing.com. ENG only
http://www.joyful-printing.net
http://www.joyful-printing.org
email: info@joyful-printing.net
With the rapid development of the electronics industry, some large-scale electronic processing companies, SMT has become the mainstream, from the earliest hand patch to the current automation equipment patch, most of them are using SMT solder paste process, but many companies have products Unavoidable production of cartridges (such as computer monitors), the emergence of earlier red glue processes and the late-wave soldering process. However, the production of red plastic process has strict requirements for wave soldering control and PCB manufacturability design. Below I will only introduce a series of requirements for the design and process parameters of the printing red glue process, which is through the bay I am currently working for. The company has conducted a year of trials to obtain effective experience and a total of SMT industry reference!
Through the test of visual intercom products, from the packaging of the device, the packaging of the jack, the rational design of the device layout, the technical requirements of the opening of the template, and the reasonable adjustment of the wave soldering parameters, the pass rate of the board welding is over 92%. (There are six 20-pin ICs and one 48-pin QFP on the product). After the wave soldering, only a small repair can achieve a 100% pass rate, but the welding efficiency is increased by more than three times compared with the manual soldering.
The following are some specific design requirements to share with SMT peers and experts.
For template thickness and opening requirements
(1) Template thickness: 0.2mm
(2) Template opening requirements: The opening width of the IC is 1/2 of the width of the two pads, and multiple small round holes can be opened.
Device layout requirements
(1) The long axis of the Chip component shall be perpendicular to the direction of the conveyor of the wave soldering machine; the long axis of the integrated circuit device shall be parallel to the direction of the conveyor of the wave soldering machine.
(2) In order to avoid the shadow effect, the ends of the same-sized components are aligned in parallel with the direction of the solder wave; components of different sizes should be staggered; small-sized components should be arranged in front of the large components; The body shields the soldering tips and pins. When it is not possible to arrange according to the above requirements, there should be a 3~5mm spacing between the components.
(3) The characteristic direction of components should be consistent. For example, the polarity of the electrolytic capacitor, the positive pole of the diode, and the single-pin end of the transistor should be perpendicular to the transmission direction, the first leg of the integrated circuit, and the like.
Component aperture and pad design
(1) The component holes must be arranged on the basic grid, 1/2 base grid, and 1/4 base grid. The gap between the plug hole of the component and the diameter of the pin is that the solder can be well wetted.
(2) Elliptical land pattern should be used for high-density component wiring to reduce the connection of tin.
Basic requirements for components and printed boards for wave soldering processes
(1) A three-layered surface mount component should be selected. The component body and the solder joint can withstand temperature shocks of more than two 260 degrees Celsius wave soldering. After soldering, the device body is not damaged or deformed, and the end of the chip component has no capping phenomenon.
(2) The substrate shall withstand heat resistance of 260 ° C / 50 s. The copper foil has good peeling strength, and the solder resist layer still has sufficient adhesion at high temperatures, and the solder resist layer is not wrinkled after soldering.
(3) The warpage of the circuit board is less than 0.8-1.0%
Wave soldering parameters design
(1) Flux system: The foaming air volume or flux injection pressure should be determined according to the condition that the flux contacts the bottom surface of the PCB: the flux spraying amount requires a uniform and thin layer at the bottom of the printed board, and the flux coating method There are two types of brushing and metering.
A The coating and foaming method must control the specific gravity of the flux. The specific gravity of the flux is generally controlled between 0.8 and 0.83.
B When the quantitative injection method is used, the flux is sealed in the container, does not volatilize, does not absorb moisture in the air, and is not contaminated, so the flux composition can remain unchanged. The key requirements of the nozzle can control the amount of spray, the nozzle should be cleaned frequently, and the injection hole can not be blocked.
(2) Preheating temperature: set according to the actual conditions of the wave soldering machine preheating zone (90-130 degrees Celsius). The role of preheating: volatilizes the solvent in the flux, which reduces the generation of gas during soldering; the rosin and active agent in the flux begin to decompose and activate, removing the printed circuit board pads, component terminals and leads The surface of the oxide film and other contaminants, at the same time protect the metal surface to prevent re-oxidation; the printed board and components are fully preheated to avoid sharp heating during soldering and thermal stress damage to the printed board and components.
Welding temperature and time: The welding process is a complex process of welding metal surfaces, molten solder and air, etc. The welding temperature and time must be controlled. If the soldering temperature is low, the viscosity of the liquid solder is too large to wet and spread on the metal surface, and it is easy to cause defects such as tipping, bridging, and rough surface of the soldering. If the soldering temperature is too high, the components are easily damaged. It will cause problems such as faster oxidation of solder joints, solder joints, and insufficient solder joints. The wave soldering temperature is determined according to the size and thickness of the printed board, the number and size of the components on the printed board. The wave soldering temperature is generally 250 degrees Celsius plus or minus 5 degrees Celsius. Since the heat is a function of temperature and time, at a certain temperature. The heat of solder joints and components is increased with time. The soldering time of wave soldering is controlled by adjusting the speed of the conveyor belt. The speed of the conveyor belt is adjusted according to the length and peak width of different types of wave soldering, for each soldering. The time of the point contact peak indicates the welding time, and the second wave soldering time is generally 2.5-4 s. Board climbing angle and peak height: The board climbing angle is generally 3-7 degrees, and it is recommended to be 5.5-6 degrees. It is beneficial to eliminate the gas generated by the flux remaining around the solder joints and components. For example, if there are fewer through holes in the design when there is SMD, the climbing angle (inclination angle) should be larger, the appropriate climbing angle can avoid the leakage welding, and the exhausting effect; the peak height is generally controlled in the printed board thickness. 2/3 and 3/4.
(3) Comprehensive adjustment of wave soldering process parameters: This is very important for improving the quality of wave soldering. Soldering temperature and time are the primary conditions for forming good solder joints. The soldering temperature and time are related to the preheating temperature, the tilt angle, and the transfer speed. When adjusting the process parameters comprehensively, first ensure the welding temperature and time. The first peak of lead double wave soldering is generally around 220-230 degrees Celsius / 1s, the second peak is generally around 230-240 degrees Celsius / 3s, and the total time of the two peaks is controlled around 4-7s. The copper content should not exceed 1%. After the copper content increases, the surface tension of tin also increases, and the melting point is also high. Therefore, it is recommended to polish the copper once a month for wave soldering. The maintenance is to set the tin furnace at about 200 degrees and wait for 4-8. After the hour, the copper-containing impurities (Cn6Sn5) on the surface of the tin furnace were collected.
Selection and use of red plastic
(1) Since it is not a dispensing process, but a printing red glue process, there is a certain requirement for the thixotropic index and viscosity of red rubber. If the thixotropic index and viscosity are not good, the forming after printing is not good, that is, collapse phenomenon, so Some of the IC's body will not stick to the red glue and be prepared. (Reference thixotropic index: 4-5; reference viscosity: (8-10) x1000000)
(2) The uncured adhesive stuck to the board can be wiped off with acetone or propylene glycol ether or with a special cleaning agent for red glue.
(3) Refrigerate the unopened product in a dry place at 2-10 °C for a storage period of 6 months (subject to the date of shipment outside the package). Before use, return the product to room temperature and return to warm for more than 24 hours.
(4) The curing time is selected to be 90-120 seconds, and the curing temperature is preferably about 150 degrees.
(5) It has good heat resistance and excellent electrical properties, as well as extremely low hygroscopicity and high stability.
Printing machine parameter adjustment precautions
(1) The pressure is around 4.5 kg
(2) The amount of red glue should be used to make the red glue roll on the template.
(3) The SNAP OFF medium distance is set to 0.05mm and the speed is set to 2 levels.
(4) The automatic wiper frequency is set to 2.
(5) After the production is finished, the red glue on the template will be discarded when it is no longer used within 5 days.
(6) Red glue must be printed accurately between the two pads and cannot be offset.