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Technical Article

Typical RoHS Issues in PCB Assembly

Time:2017-07-13 11:48:44 Click:

Shenzhen Grande Electronics has significant expertise in Prototype PCB Assembly with turn times as quick as 24 hours. Any component ranging from simple DIP resistors to BGA components with more than 1700 ball solder joints can be inserted on all available board types. Your prototype can be assembled using conventional, lead-based soldering, as well as a lead-free soldering. 

The following project checklist should be considered for any RoHs or lead-free assembly process: 
Base of Circuit Board: The substrate as well as the finishing of lead-free boards should be separated from conventional PCBs with lead-based assembly, according to industry research. Lead is not the only reason. The typical FR4 material is divided into layers because of the high temperature required for the lead-free reflow process. If rework or both-sided SMT soldering is required, the high temperature issue is magnified because the PCB will be reheated multiple times in the oven. More caution should be taken for PCBs that are primarily through-hole. From industrial feedback, an accurately calibrated reflow oven has a lower probability of causing delamination than wave soldering. A lead-free finish shouldn’t be the only requirement to consider when ordering. It is important to ensure that the manufacturer uses the correct materials that have a high-temperature tolerance and can be processed multiple times along with specifying RoHS compliance. 

RoHS Compliant Components: Verification of RoHS compliance of required components is important. Make sure there are no prohibited materials as well. When you state RoHS compliance for your required components in the Bill of Materials (BOM), the components provided in your kit must be RoHS-compliant and lead-free. As mentioned earlier, lead and the prohibited materials are not the only issue. Tolerance for higher limits is important for manufacturing processes. Even in situations where the majority of components are fine, there may be some switches, LEDs and MEMS components that are unable to perform in the higher (~50o C) temperature range. The temperature ratings of some components might just be able to let them remain functional. But it is important to keep a list of components with low temperature survivability when parts are sent to Shenzhen Grande or any other assembler. 

Moisture Sensitive Components: Over a period of time, many components absorb water in small quantities. Packages with RoHS compliance try to limit water absorption and therefore have an expiration date. An expired component or a component with open packaging can destroy itself in the reflow process because of quickly expanding water vapour, which generally causes cracks to appear on the component. Components with opened packaging or passed expiration dates can be used for prototyping but the assembly house would require slow heating for the removal of the moisture. Shenzhen Grande (like other assembly houses) usually perform a conformance check for moisture-controlled components to find out if they require heating before assembling or not. 72 hours of time is taken (at Shenzhen Grande) for the removal of moisture from components by heating. If your components have expired, the assembly process will not begin until they are properly heated. (Shenzhen Grande will contact you in this case to ask if you want components to be baked.) 

Ball Grid Array Solder: BGAs come with solder joints underneath. It is critical for BGA metallic solder balls to be exactly matched with the assembly type. Many components typically work despite being non-compliant, but BGAs will absolutely fail if non lead-free solder balls are exposed to the lead-free, reflow temperatures. 

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