smarttin, a high-quality chemical tin surface

Transcription

1 smarttin, a high-quality chemical tin surface

2 Table of contents Who is APL Oberflächentechnik GmbH?... 3 What is smarttin?... 3 Shelf life / Layer thickness...3 What are intermetallic phases?... 4 How does the process work?... 5 Process flow smarttin...5 What is the durability of smarttin?... 5 For which application smarttin may be used?... 6 Soldering...6 Press fit...6 What are the benefits of the smarttin process?... 6 Technological Benefits...7 Environmental Benefits...7 Economic Benefits...7 Further Information... 7 References... 7 Table of figures Fig. 1: Copper + smarttin... 3 Fig. 2: Layer structure smarttin... 4 Fig. 3: Layer structure Cu/ Sn... 4 Fig. 4: Schematic description of the diffusion (left Cu, right Sn) [3]... 4 Fig. 5: Schematic description after the... 4 Fig. 6: Process flow smarttin... 5 Fig. 7: ½ year storage + refresh after 3x reflow and wetting by wave soldering [4]... 6 Fig. 8: 1 year storage + refresh after 3x reflow and wetting by wave soldering [4]... 6 Fig. 9: Soldered pcb, SMD [2,4]... 6 Fig. 10: Soldered pcb, THT [2,4]... 6 Fig. 11: Soldered pcb, BGA [2,4]... 6 Fig. 7: pcb with press fit pins [2]... 6 page 2 of 7, V4.00_160323

3 Who is APL Oberflächentechnik GmbH? APL Oberflächentechnik GmbH is a service company [job plater] specialized in immersion tin (isn), isn refresh and FinalClean (ENIG/ ENEPIG). The products of APL run under the brand smarttin and FinalClean. APL is located in Lörrach (Germany). APL cooperates with all kind of printed circuit board (pcb) manufactures, electronic manufacturing services (EMS)-industries, trading companies (national/ international), and worldwide original equipment manufacturer (OEM). What is smarttin? smarttin is a trademark owned by APL and represents a "high quality isn layer" with a very strong performance. The coating is very dense and fine crystalline with an excellent corrosion resistance. The background of smarttin is 20 years immersion tin (isn) know-how, special equipment, process technology and reliable process chemistry (Stannatech 2000 H). Multiple soldering and a shelf life of up to 12 months are Fig. 1: Copper + smarttin possible. Multiple soldering includes 2 or 3 Reflow cycles as well as one wave or selective soldering step according to IPC J-STD 003B class 3 (Reflow lead-free solder process [1] ). Shelf life / Layer thickness The usual stress of 2 3 reflow cycles will survive without significant wetting deficits IPC compliant even after storage [2]. The storage time depends on the applied tin layer thickness. Storage time up to 6 months at 0.80 µm, c pk 1.33 typical tin layer thickness µm Storage time max. up to 12 months at 1.00 µm, c pk 1.33 typical tin layer thickness µm Storage conditions: C, relative humidity 75%. The max. storage time starts from the date of tinning. Through the storage time as well as by soldering cycles, the intermetallic phase grows in the layer structure. Immediately after deposition: µm After 6 months of storage: µm After 1st Reflow: µm At the 2nd Reflow: µm x Pure tin decrease total: µm respectively µm in 1 year page 3 of 7, V4.00_160323

4 smarttin is delivered with an average of µm total tin for 1/2 year shelf life respectively µm total tin for 1 year shelf life. In the worst-case standing after the 2nd reflow µm pure tin at 0,8 µm-goods or µm pure tin at 1.0 µmgoods on top for the 3rd soldering available. With the growth of the intermetallic phase decreases the free tin. This is necessary for the solderability. Intermetallic phases can generally be soldered. The only prerequisite is that they can not oxidize at the surface. They must therefore be protected (with pure tin, tin-ii-oxide and optionally a tarnish protection). Tarnish protection SnO Sn Cu6Sn5 Cu3Sn Cu some nm some nm tin (II) -Oxid µm pure tin µm η-phase µm ε-phase Cu Fig. 2: Layer structure smarttin What are intermetallic phases? Intermetallic phases are formed by diffusion of at least 2 output metals (here copper and tin). The copper diffuses into the tin layer, two phases are formed Cu 6Sn 5 (tin rich) and Cu 3Sn (poor in tin). The intermetallic phases are formed already during the deposition of smarttin. The growth of the phase depends on time and temperature, which is a natural physical process. After the maximum storage time, copper can diffuse to the tin surface through the growth of the intermetallic. Copper oxide can occur, thereby the pcbs will show a bad or even not solderable condition. Pure tin Cu 6Sn 5 Cu 3Sn Pure copper Fig. 3: Layer structure Cu/ Sn Fig. 4: Schematic description of the diffusion (left Cu, right Sn) [3] Fig. 5: Schematic description after the diffusion process [3] page 4 of 7, V4.00_160323

5 How does the process work? The smarttin -process result from three harmonized steps: Process flow smarttin The cooper surface of the pcb gets cleaned and activated by a two stage pretreatment, which optimized the following tin process. The actual chemical tin coating and activation process. It occurs through an immersion process of the tin electrolyte and the cooper surface of the pcb. A whisker Formation will be depressed sustainable because of special additives in the electrolyte. APL keeps the shares of tin, cooper and other degradation products of the deposited tin layer as low as possible. This happens among others through the coating in an inert gas atmosphere. By the last Step of the post-treatment it occurs the cleaning and drying. The pcbs obtain ionic surface contamination ultimate values which are smaller than the IPC or MIL specifications require it. For this purpose there is a special cleaning of solder mask with the product Ionix. To prevent the yellowing after the first soldering process an additional treatment of the tin surface with the product Tin PostDip 270 will be processed. Temperature [ C] time [min] Component H 2O 2 / H 2SO 4-base Stannatech 2000H Stannatech 2000H Ionix SF RT ~ 0.05 Tin PostDip stage pretreatment predipping chemical tin solder mask cleaning anti yellowing Fig. 6: Process flow smarttin What is the durability of smarttin? Performance tests Fraunhofer ISIT: Performance test of refreshed pcbs were made by Fraunhofer ISIT (2009/2014) 3x reflow resp. 2x reflow/ 1x wave soldering were performed (SAC305 Lot; Peak ~245 C) The refreshed pcbs show all very good wetting results, via-filling = 100% (acc. to IPC-A610D 75% via-filling) With the smarttin refresh process, overaged pcbs can be verifiably transformed into a solderable condition [4] page 5 of 7, V4.00_160323

6 Fig. 7: ½ year storage + refresh after 3x reflow and wetting by wave soldering [4] Fig. 8: 1 year storage + refresh after 3x reflow and wetting by wave soldering [4] For which application smarttin may be used? Soldering A composition without contamination in the tin layer is required for a perfect soldering result. The tin coating of APL is dense compact, microcrystalline and has a very low amount of pores. Through suitable measures, APL keep the process-related shares of tin (IV+) compounds, copper and other decomposition products in the deposition tin coat as low as possible. Repeated soldering is thereby possible with smarttin. A study by Fraunhofer ISIT (Institute for Silicon Technology), Itzehoe [2,4] demonstrates a clear durability and resilience of the smarttin layer. In this series of tests the pcbs actually stored for a specific period were fundamentally checked. Therefore smarttin is a 100%-replacement for H.A.L. - surface. Fig. 9: Soldered pcb, SMD [2,4] Fig. 10: Soldered pcb, THT [2,4] Fig. 11: Soldered pcb, BGA [2,4] Press fit Based on the physical features of chemical tin it s regarded as a first choice in surfaces if the further application will be press fit technology. The ca. 1.0 µm thick tin layer serves as a sliding surface in this process technology. Contact corrosion can not occur between the press-fit pin and the smarttin layer because the surface finish of the pin is the same material (tin). What are the benefits of the smarttin process? Fig. 12: pcb with press fit pins [2] The smarttin process shows a lot of benefits which are listed below. The benefits are classified in technological, environmental and economic benefits. page 6 of 7, V4.00_160323

7 Technological Benefits Environmental Benefits Plane, fine crystalline and durable metalic solder surface No tin deposition on the basic material / solder mask No entry of foreign metal into the solder connection ort he solder baths No transformation of the solder mask high ohmic No thermal stress for the pcb Subsequent e-testing is possible without any problems Carbon contact- surface coating is possible Coating of gold-contacts possible (protected with strippable paint) No negative effect (peeling, undercut) of the solder mask (when properly processed) Very resource-saving operated as a closed process. Disposal of waste (rinsing water) to the biological waste water system no additional waste water treatment necessary The smarttin refresh process permits extent a reuse of the pcb to the greatest possibility. The existing pcbs can be reused. Economic Benefits Independent of precious metal costs Cost savings because of APL stock concept A pcb refuse because of coating defects can be minimized. An overwork by smarttin coated pcbs is possible. Further Information If you need further information, please contact Mr. Dirk Kaschel. APL Oberflächentechnik GmbH Mr. Dirk Kaschel Im Entenbad Lörrach Hauingen Germany Phone.: +49 (0) 7621 / Fax.: +49 (0) 7621 / dk@apl-ssc.com web: References [1] Peak temperature <245 C; solder alloy composition Sn 96,5/Ag 3/ Cu 0,5; flux J-STD 004 Wert Lo [2] Fraunhofer ISIT performance test: 2009/09_ [3] Intermetallic copper / isn phase (diffused layer); APL, Dirk Kaschel 2015 [4] Fraunhofer ISIT performance test: 2014/11_ page 7 of 7, V4.00_160323