Ask the Experts
October 17, 2018 - Updated
January 11, 2009 - Originally Posted

Hand Soldering vs. Selective Wave for small LCD

An LCD glass display with 44 pins, 22 per side is soldered to the PCB using a manual soldering process. We are experiencing problems while soldering with a 700 degree F iron tip, and are thinking of changing this process to a selective wave soldering process. Do you recommend this approach and also do you think the effect of the high heat may cause a thermal damage to the LCD? Note that the distance between the LCD bottom glass and the PCB is 3mm.

A. M.

Expert Panel Responses

Based simply on the peak temperature a PCB experiences during selective soldering, I can confidently say that you will not have any problems soldering an LCD glass display into your assembly. Whereas your hand solder iron is at 700F as you say, most selective soldering (at least on our machines) occurs at a tip temperature of 280 Deg C or less. This has obvious advantages not just to the LCD display;in additionyou will notice an absence of measling, lifted pads, etc. on the PCB itselfwhen using a properly configured selective machine. Speaking for our company only, we have done several samples for customers that had your exact application of an LCD glass display, in addition to customers using our machines that run that application every day. It isn't clear whether the LCD is on the solder side or the secondary side from your question, however, ACE has successfully processed boards of both configurations. I would highly recommend a selective process to anyone looking to improve their through-hole process control and quality, especially if there are heat-sensitive components and PCBs (such as Teflon) that are otherwise vulnerable to a rogue soldering iron.

Jeff Fouche
Design Engineer
ACE Production Technologies
Jeff Fouche has 2 years of experience as a Manufacturing Engineer for CM/OEM and 2 years as a Design/Process Engineer with ACE Production Technologies. Jeff is also an IPC certified trainer. He received his BSME in 2003 from the University of Idaho.
NOTE: Mr. Fouche is no longer working at ACE production Technologies.

While we would suggest much more testing before recommending any process, soldering at 700F (370C) is a higher temp range and could require additional considerations. It would also be good to understand if the LED was placed with the pins facing upward, or if this was a through hole application currently being flipped and hand soldered. Soldering from the top side with a flux core solder and hot iron tip could work better if: perhaps the joint area(s) was pre heated with hot air, the amount of solder was controlled for each joint, and the applied heating time was programmable for each joint, should there be any thermal profile differences. Soldering from the bottom could yield good results but consideration should be given to: how the precise amount of flux is applied to only those areas/joints desired, The effects of higher temperatures on the soldering pot and the results of additional maintenance, fumes that result from bottom side soldering getting onto the glass LED surface, and possible bridging (if joints are too close together). Typically, robotic type iron tip soldering can provide a very reliable and repeatable method to solder these types of applications. Cycle rates and volumes would need to be considered since the iron tip systems are a Point to Point soldering method. Samples could be sent to several vendors for soldering allowing you to view results with little investment.

Gary Goldberg
President and CEO
Mr Goldberg has practical experience in production line layout, process flow and cycle rate analysis. He knows how to avoid bottle necks and most related PCB or pallet handling questions.

Millions upon millions of LCD displays have been selectively soldered using both mass-selective wave and miniature-selective wave (drag) soldering process. It is a very reliable process that is much more robust than hand solder, and much more cost effective. The process is used for both lead and lead-free applications in automotive, aerospace and other applications. Typical solder times range from 15-seconds per LCD (mass-dip) to a maximum of 1-second per termination in drag solder.

Jess Baker
RPS Automation
Jess Baker has been in manufacturing management positions for over 47 years. He is the President and founder of Repco Inc., and Robotic Process Systems. He is currently President of RPS Automation a manufacturer of Selective Soldering, and Solderability Test Equipment.

individual preforms or integrated preforms to:
  • solder all pins in1 shot
  • eliminate manual soldering & solder iron (just use heat gun for hot air to melt solder)
  • achieve the same volume of solder from pin-to-pin

Karthik Vijay
Technical Manager - Europe
Indium Corp.
Currently with Indium Corporation and responsible for technology programs and technical support for customers in Europe. Over 15 yrs experience in SMT, Power, Thermal & Semiconductor Applications. Masters Degree in Industrial Engg, State University of New York-Binghamton.

I would suggest using a stencil to apply paste and yes wave the LCD with a controlled reflow oven that you can profile and save the procedure for later projects and re-runs. I can't tell you if the LCD can handle the temperature without reviewing the components specification but I assume you have. Non leaded or leaded process is very different in temperature but I would say reflowing with conveyorized unit will do very nicely.

James Mahoney
Applications Project Manager
Quick Turn Flex Circuits LLC
James Mahoney is a Technical Operations Manager with a 20 year track record in managing new product introduction. He is a skilled leader, motivator and problem solver with a strong background in Product Knowledge and Engineering Management.

I would recommend soldering the LCD glass display with 44 pins to the PCB using a selective wave soldering process, as the selective wave offers a totally controllable and consistent soldering process, eg the temperature of the wave, the wave height, travelling speed and angle of the PCB (dwell time at each pin), the soldering environment (nitrogen gas surrounding the soldering process) and amount of flux applied at each pin. The advantages using the manual soldering process is the low cost of the manual soldering station vs the high cost of the selective wave soldering machine, and machine size. 3mm clearance is not a problem, for a standard selective wave soldering machine. There are some high end models that can accept as close as 1mm clearance between soldering pads.

EH Lim
Managing Director, Asia Pacific
EH Lim has been in the PCB Assy industry since 1985, starting at Thomson/Singapore for 5 years before moving to Electrovert Asia Pacifc. Lim was Sales Director for Vitronics Soltec prior to joining ECD in 2007 as Managing Director for Asia Pacific.

Reader Comment
Selective soldering is a good option for this application, specifically using a mini-wave process. Depending on the thermal requirements of this LCD, the heat transfer can be controlled by the specific process parameters. These include mini-wave nozzle size, dwell time, and wave height. A selective soldering process will also be better controlled than hand soldering, assuring better consistency both in the soldering process and in fluxing and preheating.
Mike Korte, SEHO North America

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