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• Requirements pt1 - High-level System (WIP)

  Devin • 03/30/2024 at 13:15 • 0 comments

  Project Goals

  1. A usable hotplate reflow soldering station
  2. Practical experience with:
     1. USB-PD
     2. Displays (e.g. TFT)
     3. HMI beyond basic pushbuttons (e.g. haptic knobs or touchscreen, even keypads)

  High-Level Requirements

  1. A user must be able to reflow solder a one-sided PCB with pre-pasted, pre-placed standard* SMD components.
  2. The user must be able to control the reflow thermal profile for different paste liquidus temperatures.
     1. The user should be able to control the rate of temperature increase to prevent thermal shock.
  3. The user must be able to supply power with a USB-C cable (via USB-PD).
  4. The  system must provide the user some visual indication of:
     1. the thermal profile used
     2. the progress, stage, and/or time of a running reflow process.

  *Standard SMD components meaning SMD components that have pads on only one-side (Top), lay flat on the PCB, have no special thermal considerations, and no other special reflow/soldering requirements.

• Core Component Selection Notes

  Devin • 02/09/2024 at 12:48 • 0 comments

  MCU

  x CH552 

  STM32G031J6 (link): no USB, 8pin package

  STM32F042F4 (Link): USB2.0, 1x 12bit ADC

  Temperature Sensors

  PT100 (ADC)	P0K1.232.6W.Y.010	€ 6.08 / 1	€ 3,32 / 1ku
  PT100 (ADC)	PTFC101B1G0 (datasheet)	€ 2,81 / 1	€ 1,34 / 1ku
  Thermistor (ADC)	NTCLE203E3104GB0A (datasheet)	€ 1.42 / 1	€ 0,589 / 1ku

  Heater

  MCH selected. Its purchasable in various sizes, voltage/power ratings.

  A 50mm x 50mm 24V 70W MCH was purchased as a sample from AliExpress

• Research - Other Reflow hotplates

  Devin • 02/09/2024 at 11:52 • 0 comments

  Toby's Automatic MCH PD Reflow Hotplate

  (tindie, git-imuslab, hackster.io, CH554 SDCC)

  A USB-PD powered metal ceramic heater (MCH) based reflow hotplate.

  Key Features:

  • USB-PD
  • MCH
  • Fully automatic (and any changes requires reprogramming the IC)

  System Info

  Controller	CH552G (Arduino Programmable)
  Power Input	USB PD 20V 3A (60W / 65W PD power supply recommended
  Interface	1 button Press and hold to start
  Profile Change	reprogram over USB
  Cooling	no

  Hotplate

  Hotplate Type	MCH (Metal Ceramic Heater)
  Hotplate Size	40mm * 40mm (± 1mm)
  Hotplate Power Consumption	30..50W

  Temperature Sensor

  Temperature Sensor	100k 1% Thermistor (example, datasheet)
  Temperature Sensor (Controller)	ADC on-board MCU (8bit)

  Components

  • CH552G 
    • 8bit MCU (16pin)
  • IP2721
    • USB-C/PD physical layer IC (datasheet)
  • TPS259261
    • 12V eFuse protection switch
  • AO3400A
    • n-channel MOSFET 30V 5.7A 1.4W

  Connectors

  • 4p (2x2) 100mil "PROG1"
  • 2p 100mil "SENSOR"
  • 2p screw terminal 5.00mm
  • 3p 100mil

  ICs Not Shown

  • L7805CD2T (U5)
    • LDO 5V 1A (datasheet)
  • IRLR8726T (U7)
    • N-channel MOSFET 30V 86A 75W (datasheet)

  Unlisted part

  • 2-wire 100k 1% Thermistor
    • with 1k at 240° and a 100k NTC at 25° (utils.ino) --> Beta ~4000

  Solder-Reflow-Plate by AfterEarth

  (github, homepage)

  A 12V barrel jack powered PCB hotplate.
  

  Key Features:

  • PCB heater
  • OLED display

  System Info

  Controller	ATmega4809 (Arduino)
  Power Input	12V 5A Barrel jack
  Interface	2 pushbuttons and OLED
  Profile Change	pushbuttons (select Zone temperatures)
  Cooling	no. Temperature is displayed during cooling

  Hotplate

  Hotplate Type	PCB trace resistors
  Hotplate Size	70mm * 50mm (± 1mm)
  Hotplate Power Consumption	~30W

  Temperature Sensor

  Temperature Sensor	LMT85LP (datasheet)
  Temperature Sensor (Controller)	ADC on-board MCU (10bit)

  Note: the temperature range of the LMT85LP is limited to 150°C.

• Research - Reflow soldering

  Devin • 02/09/2024 at 09:28 • 0 comments

  Reflow Zone

  Reflow soldering can be divided into several Zones:

  Zone / Ramp to Zone	Temperature	Slope	Time
  Ramp to Soak	20°..soak	1..3°/s (2°/s)	45s..130s (60s)
  Soak	150° (typ.)	-	60s..120s (120s)
  Ramp to Reflow	soak..230-250°	1..3°/s (2°/s)	25s..100s (50s)
  Reflow	230-250° (Liquidus + 20-40°)	-	30s..75s (45s)
  Cooling	230-250°..75°	-2..-10°/s (-4°/s)	15s..90s (60s)

  During the reflow process, the most important factors of each zone are:

  • Temperature: too low and nothing happens, too high and undesirable things happen.
    For example, during in the thermal soak zone, solder paste volatiles are removed and the flux is activated. 
  • Too high a temperature can cause solder splattering, balling, oxidation of the paste/pads/component terminations.
  • Too low a temperature and the fluxes are not activated nor are the volatiles removed.
  • Slope: heating causes thermal stress. Heating too quickly can lead to thermal shock and cracking. This is less important during cooling although it still has an impact on quality.
  • Time: the effects of each zone take time to occur.

  Reflow Process Evaluation

  Electronics Manufacturers evaluate their processes using PWI (Process Window Index) with 4 primary metrics:

  • Slope
  • Soak Time Between lower and upper soak bounds
  • Peak Temperature
  • Time above Liquidus (TAL)

  PWI can be considered in future (possibly).

  (reflow soldering wikipedia) (IPC-7530) (Tronstol)

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