Device soldering is an easy skill to learn if you understand what to look for when you are completing your work. Having clean equipment is a must. Any corrosion or contamination on your soldering equipment, the printed circuit board or component leads will lead to soldering failures. The next step is using the current heat settings and tip size. The tip must be small enough to allow for good mechanical connection to the lead and the foil from the time of the iron and tip. The time you leave the iron on the connection can very slightly, you need toconcentrate on the connection and watch for the flow of the molten solder. The final steps are also critical, they are first to allow the solder to harden, then inspect and clean the rosin off the board and solder connection.
Remember , it takes just a second to inspect your work ; it may take a technician hours to find your fault.
Advanced soldering techniques-surface mount soldering
When working with surface mount device and high density printed circuit boards extra care must be taken in handing and storage. A surface mount board has an extremely high density of part over a very small surface area. Parts are extremely small. A typical component could fit inside a single character on this text. Many surface mount parts are staticsensitive,Which means that static electricity can weaken or destroy the part. The individual that induces the damage into the part may not feel the static electricity. Be sure that you follow all static controls when handling parts, boards or when soldering on these boards.
Caution–Do not attempt to work on surface mount boards without authorization and training. Practice should be done on scrap equipment until you are sure of your skills to do this work. Surface mount soldering requires special equipment techniques. Using the correct equipment and techniques make this work systematic, but you need patience and a steady hand when working with extremely small parts.
Surface mount device–Some device are not much larger than a grain of rice, each part, even very small ones will have a part number, polarity marking and some even a company logo on the top of the part. You will not be able to read this text without a microscope like reading device to magnify the lettering.
To work with surface mount devices you will need the following tools
1.Anti-static workstation
2. Anti-static ankle, or wrist straps, and connecting cord
3. Magnification tools and lenses Hot air willmeltsolder paste and solder
4. Silver solderpaste the part to the land area-move the tip
5. Cleaning tools and chemicals around the part until the silver solder paste
6. Vacuum de-soldering/soldering stations melts to attach the component to the board
7. Masking tape
8. Ventilation equipment
Soldering of a component
Components are solders on landing areas through the following techniques
- Clean area of corrosion and contamination
- Apply solder paste to land area
- Apply hot air to solder part
- Clean board area
Steps to attach a surface mount chip to a board with components
- Apply type lightly to areas around the surface mount device- tape is optional based on board density
- Clean foil area
- Apply silver solder paste to foil areas
- Lay the part exactly over foil pattern on paste
- Hold part in place and apply hot air to foil areas
- After soldering paste melts into foil-clean board
- Remove tape and clean board for any residue
- Clean and inspect between each lead
- Test chip operation
Note : Application of the tape is optional
Removal of surface mount integrated circuit chips
To Remove an integrated chip, care must be taken to not remove adjacent parts. Due to the high density of parts on the board, hot air can blow off other parts. I find it useful to shield close parts with tape, this is an optional step that will take a little extra time but can save trouble later on in the process. Timing is important with soldering and de-soldering; it is critical in removal of chips. In soldering or removal of surface mount devices.direct soldering on the board of component is not done, only the use of air will remove or attach surface mount device. In removing a surface mount integrated circuit, based on its size a circular pattern of motion with the hot air will be appliedfrom the center to the outside of the chip. A removed device is disposed of, not re-used. De-soldering will damage the chip.
There are other methods that can be used with non -air direct contact soldering equipment systems to remove surface mount devices, they are used by experienced technicians and should not be attempted without authorization. The following method using hot air will require practice; before you attempt to remove a part from a good board, it is recommended to get enough practice on scrap board to perfect your abilities.
Using circular motions starting in the center move the hot air first around the part from inside out then outside in – heating the part while pushing down gentle on the corner of the component. When the solder melts the part will lift off the board from the pressure on the corner. After you remove the hot part, switch the vacuum on and remove all the solder from the foil area, and clean the board area
Removal of surface mount devices
Removing a surface mount device – 2 or 3 leads is accomplished by application of hot air, moving the nozzle across the part. When the solder melts, then lift the part off the board. The vacuum suction will then collect all lose solder, you then clean the board area.
The use of a vacuum desoldering device on multi – layered boards
When through hole desoldering is done on multiple layered boards, care must be taken protect the foil connections on both sides of the board and those that are embedded within the board itself.
Surface mount boards may have multiple layer of foil patterns on both sides of the boards and additional foil embedded into the board layers. When removing solderfrom these componentleads it is important that the board connections are not broken during the de- soldering process. A vacuum tip is used to melt then vacuum out the molten solder. After all solder has turn to a molten state, a vacuum is applied to the connection. A gentle circular motion is given to the lead as the vacuum removes loose solder around the joint. If the lead does not easily come loose then re- solder the connection and do the process over again.
Static control applications
Using static electricity controls can involve the following areas
- Room – environmental controls
- Air filtration
- Anti-static chemical applications on surfaces
- Anti-static carpet and desktop materials
- Transportation and storage
- Static protection bags
- Anti-static foam
- Personal protection
- Anti-static wrist straps
- Anti-static ankle straps
- Anti-static clothing
- Aprons
- Socks
Protection of devices involve the entire life cycle of the product. The cycle starts by proper storage of components and assemblies in anti -static bags and foam, then the room for production has environmental controls, for lowed by personal controls. You must maintain controls throughout the entire process.