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Surface metal layer
The industry mostly use green solder "silver copper tin" formula HASL (Sn Ag - 3.9-95.5 0.6 Cn) instead of pewter, environmentally friendly lead-free PCB surface coating layer should have high wetting liquid, smaller thermal stress, high temperature is not easy oxidation features, facilitate lead-free SMT processing.In addition, flux, a synchronization is required to adopt green HASL is poor, and they have mutual fusibility with SMT solder.
Ink
Ink on the PCB leaving include: solder resist ink, printing ink, jack inks, ink composition with plank, mainly containing resin, bromine flame retardants and curing agent, at present many brand ink has do not contain harmful, such as Japan, taizhou, the new Korean ink the sun.The choice of ink must not only conform to the requirements of environmental protection, and to withstand environmental protection lead-free SMT long time high temperature for many times, not hierarchical discoloration, peeling, crack phenomenon.
Control of lead-free materials
The management of raw materials is very important one link in green PCB production, such as tin, so long as has the lead article tin was mistakenly add pure tin bath will lead to disastrous consequences, and indirect materials such as flux residues also nots allow to ignore, specific countermeasures include: (1) establishing that the encoding rules of the halogen free lead-free materials;(2) using color logo, on the inner and outer packing printed with "green" label to be approved by IQA.(3) in the warehouse and production site, to separate storage for environmentally friendly raw materials, production site personnel to add;(4) to realize "green qualified suppliers" certification program.
The choice of lead-free process and control: the selection of lead-free PCB surface coating layer process include: Ni/Au plating, chemical immersion Ni/Au, OSP (organic run-off protection agent) chemical tin Sn and chemical heavy silver Ag.
The import of lead-free process steps
CAM design
Environmental protection engineering design of PCB is basic aspects, lead-free process after the CAM should take into account the SMT process influence on the function of the PCB.
Graphic design examples (wiring, welding area shape)
1. prevent immersion flow insert parts left, red eye diameter welding area a little bit small.
2. Prevent immersion flow QFP bridging QFP tilt 45%.A dummy welding area.
3. To prevent the soft melting chip separation illuminates the basic in the past.To make the protective film: opening near it.
Prevent substrate warp
Technology development
Process of the development and management is important link in the production of environmental protection PCB, specific countermeasures including:
(1) environmental protection and environmental protection materials do not collinear or mixed line production, such as: enhancement and finished products to clean.
(2) in the MI process of paper, with environmental protection product operators, and sign the MI confirmed its, lead-free process remind now field operation department staff.
(3) environmental protection product production facilities, tooling, visual management, with prominent logo distinguish.
(4) ink has to withstand environmental protection lead-free SMT long time high temperature for many times, so the pretreatment, substrate drying is a very important link, the printing ink after spray tin or lead free HASL SMT, the possible defects of the ink on the side of hole stripping is mainly hole, floor water residue, high temperature when inflation and make the ink and copper layer separation.
(5) solder resist ink is not allowed to add rare ze agent, which can avoid high temperature circumstances hole ink residue solvent volatilization sharply inflation caused by the blasting hole.6 HASL Cu content in the tin bath to control below 0.85%.
reliability assessment
Therefore, environmental protection PCB products reliable test compared to the environmental protection PCB, but also improved the following experiments:
(1)Solderability test.(solderability test furnace with lead-free solder environmental requirements of SMT solder or HASL consistent)
(2)thermal shock test.Condition: - 40 ℃ / 85 ℃ / 85 ℃, no crack after 3000 times.
(3)the thermal cycle test.No crack, shrinkage cavity appear.
(4)constant temperature and humidity test.Condition: 60 ℃ 90-95% RH, 500 hours, under high temperature and high humidity for a long time do not produce metal products.
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