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Electronics Buyers' Guide

Electronics Manufacturing & Production Handbook 2019


 

Stencil underside cleaning and manual post-cleaning
27 February 2019, Manufacturing / Production Technology, Hardware & Services

According to experts, between 60 and 70% of all defects and failures during or after the soldering process are attributable to defects in the printing process (Figure 1). In general, these are faulty solder joints, which in turn have their causes in solder paste printing mistakes. Therefore, the stencils used in the assembly process must already be cleaned during the printing process – if not, soldering errors caused by luting and bridges are inevitable.

Figure 1. Approximately 64% of process-related failures are related to deficits in the entire printing process.
Figure 1. Approximately 64% of process-related failures are related to deficits in the entire printing process.

Especially in the fine and ultrafine pitch range, many details are no longer visible to the naked eye (a stencil designed for wafer production can easily have more than 300 000 apertures). Microscopic carry-overs cause a noticeable loss of quality or lead to later failures or rework, which can amount to about 25% of the manufacturing costs of an assembly.

Figure 2. The stencil area alone is responsible for almost half of the total failures.
Figure 2. The stencil area alone is responsible for almost half of the total failures.

It is realistic to assume that the failure rate of 15% each during picking-and-placing and soldering would also be of a similar value for the machine printing performance, considering the use of always perfectly new and cleaned stencils. As a reverse conclusion, this means that almost 50% of process-related failures – besides wear and tear – are attributable to poor or inadequate cleaning of the relevant production tools like stencils and squeegees (Figure 2).

In order to ensure a qualified printing process in an SMD screen printer as long as possible before the stencil has to be externally machine cleaned, it is necessary to clean the underside of the stencil from flux residues already inside the screen printer.

In modern screen printers, this usually happens during the process through an automatic bottom cleaning unit, using cleaning fleeces and a suitable ready-to-use detergent. A suitable stencil cleaner for use in screen printers – such as kolb’s WipeEx SA120, which has been specially developed for this purpose – offers qualified and efficient cleaning performance due to the following factors:

Figure 3. Stencil apertures before and after cleaning with Wipex SA 120.
Figure 3. Stencil apertures before and after cleaning with Wipex SA 120.

• Optimal flow and wetting properties

• One-phase (aqueous, stable)

• Cleans SMD paste and SMD glue

• Cleans in contaminated state

• Fast, residue-free evaporation/ drying

• Does not change the viscosity of the adhesive

• Does not cause polymerisation (curing) of the adhesive

• No classification as a dangerous good

• Non-critical flash point (optimal >120°C)

• Biodegradable (92% after 28 days [OECD Test 301A])

• Low odour (with fresh scent)

In certain cases, manual (re)work on the stencils may be necessary; or, when it comes to cleaning squeegees by hand, to avoid carryover here too. For that kolb offers WetWipes, WipeEx’ SA120 impregnated, ready-to-use cleaning wipes with a cleaning fleece especially for stencils with fine apertures, low to no particle delivery, even soaking, and high elasticity/tear strength with high absorption of the medium or paste mixture.


Credit(s)
Supplied By: Testerion
Tel: +27 11 704 3020
Fax: 086 555 0111
Email: info@testerion.co.za
www: www.testerion.co.za
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Further reading:

  • Continued success for Zetech’s stencils division
    30 April 2019, Zetech, Manufacturing / Production Technology, Hardware & Services, News
    Best known for supplying SMT (surface mount technology) equipment and consumables for printed circuit board assembly for 33 years, Zetech is enjoying success with its more recently established stencils ...
  • How to analyse blind via hole failures
    27 March 2019, This Week's Editor's Pick, Manufacturing / Production Technology, Hardware & Services
    It has become common practice to use blind, filled and stacked vias in many portable electronics products. Experience has shown that this method of interconnection is reliable, provided the fabrication process is well defined and controlled.
  • PCB microsectioning – paying attention to detail
    27 March 2019, Cirtech Electronics, This Week's Editor's Pick, Manufacturing / Production Technology, Hardware & Services
    In our high-tech world, it’s easy to overlook the importance of the humble printed circuit board (PCB). Buried in each electronic gadget or appliance there’s always at least one PCB and each one has ...
  • X-ray dose considerations
    27 March 2019, MyKay Tronics, Manufacturing / Production Technology, Hardware & Services
    The benefits of using X-ray technology in the electronics industry to inspect printed circuit board assemblies are well proven. This article summarises X-ray radiation dose, and the techniques that ...
  • Product development issues explored in new video
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    Printed circuit broker, Elmatica, recently released a new film about product development, explaining why cooperating with an experienced partner could be a smart move. “We have several times seen the ...
  • Flux management system earns APEX award
    27 March 2019, MyKay Tronics, Manufacturing / Production Technology, Hardware & Services
    BTU International was awarded a 2019 NPI award in the reflow soldering category for its new Aqua Scrub flux management technology. The award was presented to the company during a ceremony that took place ...
  • Solder dross recovery system
    27 March 2019, Electronic Industry Supplies, Manufacturing / Production Technology, Hardware & Services
    Stannol’s Solder Saver is a mechanical device to reduce dross, which occurs as an unavoidable side effect in wave soldering systems. According to its manufacturer, solder consumption can be reduced by ...
  • Water-soluble solder paste
    27 February 2019, Techmet , Manufacturing / Production Technology, Hardware & Services
    Indium has released Indium6.6HF solder paste – a new water-soluble, halogen-free solder paste that is compatible with both tin-lead and lead-free alloys. It is designed to provide enhanced stencil printing ...
  • Affordable soldering station
    27 February 2019, Electronic Industry Supplies, Manufacturing / Production Technology, Hardware & Services
    The Industa 550 soldering station, available from Stannol, is an affordable unit characterised by easy operation and universal fields of application. The temperature is easy to set using a potentiometer, ...
  • What you need to know about the Hermes standard
    EMP 2019 Electronics Manufacturing & Production Handbook, Manufacturing / Production Technology, Hardware & Services
    Taking advantage of modern TCP/IP communication and XML data format technologies, Hermes is effectively a replacement of the more than 20-year-old SMEMA standard.
  • Contract electronics manufacturing in SA
    EMP 2019 Electronics Manufacturing & Production Handbook, Leratadima Tellumat Manufacturing, Manufacturing / Production Technology, Hardware & Services
    We asked representatives from two leading South African contract electronics manufacturers to share some of their insights into this complex landscape.
  • BGA optical joint inspection criteria and test methods
    EMP 2019 Electronics Manufacturing & Production Handbook, Manufacturing / Production Technology, Hardware & Services
    BGA failures occur for component, printed board, process or design related reasons, and on some occasions, both X-ray and optical inspection cannot easily provide the answer.

 
 
         
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