Frequently Asked Questions

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Q. What is a Solder Stencil?

An SMT stencil is a precision laser cut stainless steel foil that contains apertures precisely matching the pcb's surface mount component footprints. The stencil is used to dispense the correct amount of solder paste onto the component pads and is a speedy way to lay down many deposits of solder exactly where you need them in a short period of time. Our stencils are supplied in a pre-tensioned frame and each is 100% scanned for accuracy.

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Q. What is Solder Paste?

Solder paste is a mixture of powder like alloy solder spheres (tiny metal balls) that are coated with a layer of flux. All metal surfaces have a thin film of oxidation or passivation that acts as a barrier, caused by normal environmental exposure to air. Flux is a chemical product (usually rosin-based) that prepares the metal surfaces for soldering by cleaning off oxides, passivation and other contamination. The specialised flux used in solder paste serves two functions. It provides a protective layer to the metal (to keep it from building an oxidation barrier) and is a semi-fluid media that carries the metal during application. Solder works by melting when it is heated, and bonding (wetting) to metallic surfaces that the flux has "prepared" to accept it. The solder forms a permanent intermetallic bond between the metals joined, essentially acting like a metal "glue."

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Q. What is Reflow Soldering?

Reflow soldering is the means to attach a surface mounted component to a circuit board, by applying solder paste, positioning the device, and reflowing the solder in a multi-zone oven. The goal of the reflow process is to melt the powder particles in the solder paste, with the surfaces being joined together, and then solidify the solder to create a strong metallurgical bond. There are four temperature zones in the reflow process, consisting of preheat, thermal soak, reflow and cooling.

The first zone is a preheat in which the circuit board and components are heated at a controlled maximum rate so as not to introduce thermal shock . The solvents in the paste begin to evaporate. During the second zone, thermal soak, the volatiles are removed and the flux begins activation on the metal oxides. By the end of the soak zone thermal equilibrium of the entire assembly is desired, just before the reflow zone. The third section, or re-flow zone, is the region where the maximum allowable temperature of the process is reached. During this peak temperature the solder becomes a liquid and the flux reduces the surface tension between the junctions of the metals allowing the solder powder spheres to combine and metallurgical bonding to occur.

If the profile exceeds the paste manufacture’s specifications the result may be premature flux consumption, effectively ‘drying’ the paste before formation of the soldered joint. An insufficient curve causes a decrease in the flux’s cleaning action, resulting in poor wetting. Additional time in the liquid solder stage can cause a brittle joint, as well as damage to the board or components.

The last zone is a cooling zone, to gradually cool the processed board and solidify the solder joints, once again avoiding thermal shock.

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Q. How do I ensure my component footprint is to IPC standards?

Contact us for a free IPC standards library and viewer.

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Q.What is RoHS

From July 2006 Producers placing new electrical and electronic equipment on the EU market must ensure that they comply with the directive covering the Restriction of Hazardous Substances or RoHS. It is for the Producer to decide if their products, including electronic sub-assemblies, are covered by the directive and if so must not exceed the maximum permitted concentrations of six substances, including lead. Exemptions to the regulations exist for certain industrial applications.

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Q. Will my assemblies be RoHS compliant?

Cope Technology have no automatic requirement to build without lead as we are not classified as a Producer under the definition in the regulation. However, we do have both lead and lead-free options for all soldering applications. When requested, our quality system has a defined process which we employ to minimise the risk of contamination and ensure compliance. Once a product is qualified as RoHS, it will always be manufactured compliant.

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Q. What are the considerations if I want my products to comply with the RoHS directive?

When a customer asks about the transition of an existing product or the introduction of a new product to be RoHS compliant, there are two main considerations.

  1. Are all the component parts and pcb available in a compliant form?
  2. Will processing at the higher lead-free temperatures cause any unforeseen consequences?
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Q. What is Cope's experience with transition to RoHS?

Components have become lead-free at various times over the last decade, and since 2004 our stock control has identified RoHS parts which we then exclusively ordered. Our preferred choice of PCB finish is either lead-free HASL or immersion gold, so by 2006 most assemblies were built with lead-free parts and leaded solder. To offer a compliant process we had to invest in a second flow soldering machine, a new multi-zone reflow oven and temperature controlled hand soldering irons.

There are technical hurdles to using lead-free solder. The elevated melting point narrows the process window and joint formation can look different. Retraining for inspection and hand soldering have all added extra time and cost to production. However, we are satisfied our carefully selected solder pastes, fluxes and optimised process control result in a qualified RoHS compliant product. The majority of products are now processed lead-free.

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