PCBA cleaning method, cleaning process, PCBA cleaning machine, flux cleaning (1)

After the PCBA is cleaned, the board surface turns white, what should we do?

After the circuit board is cleaned, the board surface turns white, what should we do?

Edited by Ming: ming@smthelp.com

First, the board surface is whitish after cleaning:

In the electronic component manufacturing process, the PCBA circuit board is often over-wave soldered, and after the manual cleaning agent is used for cleaning, the board surface appears white (Figure 1).

PCBA cleaning method, cleaning process, PCBA cleaning machine, flux cleaning (1)
PCBA cleaning method, cleaning process, PCBA cleaning machine, flux cleaning (1)
Figure 1
After the cleaning of the PCBA solder joints, the white surface of the board surface appears after being placed, and the white mark is scattered around the solder joints, which seriously affects the appearance acceptance.

Second, the reason for the whitish surface of the board after cleaning:

White residue is a common contaminant on PCBA and is generally a by-product of flux. Common white residues are polymerized rosin, unreacted activator, and lead metal chloride or bromide, which react with flux and solder. These substances expand in volume after moisture absorption, and some substances also hydrate with water. White residue is becoming more and more obvious. It is extremely difficult to remove these residues on the PCB. If the temperature is too hot or high, the problem is more serious. The infrared spectroscopy analysis of the rosin and residue on the PCB surface before and after the soldering process confirms the process. .

PCBA cleaning method, cleaning process, PCBA cleaning machine, flux cleaning (1)
PCBA cleaning method, cleaning process, PCBA cleaning machine, flux cleaning (1)

Regardless of whether the board has white residue after cleaning, or if the white material appears after the no-clean circuit board is stored, or the white substance on the solder joint found during the repair, there are four cases:

  1. Rosin in the flux: Most of the white matter produced after the cleaning is not clean, stored, and the solder joint fails, is the inherent rosin in the flux. Rosin is usually a transparent, hard and brittle solid material with no fixed shape, not a crystal. Rosin is thermodynamically unstable and has a tendency to crystallize. After the rosin crystallizes, the colorless transparent body becomes a white powder. If the cleaning is not clean, the white residue may be a crystalline powder formed by the rosin after the solvent is volatilized.

When the PCB is stored under high humidity conditions, when the absorbed moisture reaches a certain level, the rosin gradually changes from a colorless and transparent glass state to a crystalline state, and a white powder is formed from a viewing angle.

PCBA cleaning method, cleaning process, PCBA cleaning machine, flux cleaning (1)
PCBA cleaning method, cleaning process, PCBA cleaning machine, flux cleaning (1)

The essence is still rosin, but the shape is different, still has good insulation, and will not affect the performance of the board. The abietic acid and halide (if used) in the rosin are used together as an active agent. Synthetic resins generally do not react with metal oxides below 100 ° C, but react rapidly when the temperature is higher than 100 ° C. They volatilize and decompose faster, and have low solubility in water.

  1. Rosin denature: This is the substance produced by the reaction of rosin and flux during the welding process, and the solubility of this material is generally poor, it is not easy to be cleaned, and it stays on the board to form a white residue. But these white substances are all organic, still guarantee the reliability of the board.
  2. Organometallic salt: The principle of removing the oxide of the welding surface is that the organic acid reacts with the metal oxide to form a metal salt soluble in liquid rosin. After cooling, it forms a solid solution with the rosin, and is removed together with the rosin in the cleaning.

If the welding surface and parts are highly oxidized, the concentration of the product after welding will be high. When the degree of oxidation of the rosin is too high, it may remain on the board together with the undissolved rosin oxide. At this time, the reliability of the board will be reduced.

  1. Metallic inorganic salts: These may be metal oxides in solders and halogen-containing active agents in flux or solder paste, halide ions in PCB pads, halide ion residues in the surface coating of components, halogen-containing materials in FR4 materials. The substance formed by the reaction of the halide ion released at a high temperature generally has a small solubility in an organic solvent.
PCBA cleaning method, cleaning process, PCBA cleaning machine, flux cleaning (1)
PCBA cleaning method, cleaning process, PCBA cleaning machine, flux cleaning (1)

In the assembly process, it is highly probable that the halogen-containing flux is used for the electronic auxiliary materials (although the supplier provides environmentally friendly flux, but the halogen-free flux is still relatively small), and the surface of the board remains after welding. Halogen-based ions (F, Cl, Br, l). These ionic halogen residues, which are not themselves white, are not sufficient to cause whitening of the surface. These substances form strong acids when exposed to water or moisture. These strong acids begin to react with the oxide layer on the surface of the solder joints to form acid salts, which are white substances that are seen.

Third, after the circuit board is cleaned, the board surface is whitened:

1, the general solution:

  1. Washing method Note: When washing the PCB, the PCBA should be tilted. Do not lay it flat. You can place the paper in the washing station, so that most of the washed solution will flow down;
  • Do not wash the plate repeatedly for repeated times, and increase the frequency of replacement depending on the situation;
  • 3, and then start from the washing water formula, you can ask the supplier to improve the formula, improve the cleaning degree and dissolution volatility.

    1. How to completely solve the problem of whitening of the board after cleaning the circuit board?

    For the whitening problem of PCBA circuit board cleaning, water-based cleaning agent can be used to meet the corresponding cleaning equipment to deal with it. It is safe and environmentally friendly, meets the requirements of current ROHS, CE, and other environmental protection regulations. It has high cleaning efficiency and completely solves the problem of whitening.

    SMTHELP :SMT Professional Manufacturer PCB Cleaning Machine
    The product is suitable for use in automotive electronics, smart home products, communications electronics, consumer electronic product manufacturing process, to improve product reliability and to remove foreign bodies and electrostatic PCB surface
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    PCBA CLEANING MACHINE SCM5600D (2)
    PCBA CLEANING MACHINE SCM5600D (2)

    Automatic PCBA cleaning and drying machine for EMS factory

    Our high performance cleaning machines are designed to remove all unwanted contamination present in electronic manufacturing and micro-mechanic

    WATER BASED ELECTRONIC PCB CLEANING MACHINES – For printed circuit boards, flux no-clean, solder paste misprints, small parts.

     

     

    An Analysis of SMT Solder Paste Printing Defects

    An Analysis of SMT Solder Paste Printing Defects

    In SMT PCB production, solder paste printing is a critical step. Since the solder paste is used to directly form the soldering joint, the quality of solder paste printing affects the performance and reliability of the surface mount assembly. Quality solder paste printing guarantees a quality solder joint and final product. Statistics demonstrate that 60% to 90% of soldering defects are related to solder paste printing defects. So it is very important to understand what causes defects in solder paste printing.
    ItemFactorsAnalysis1Solder PastePowder formationThe irregular shape of solder powder will easily clog stencil apertures. This will cause a big slump after printing. It can also cause solder ball and short bridge defects after reflow.

    A spherical shape is best, especially for fine-pitch QFP printing.Particle SizeIf the particle size is too small, the results will be poor paste adhesion. It will have a high oxygen content and cause a solder ball after reflow.

    The particle size should be controlled to about 25 ~ 45 μm in order to meet the requirements for fine-pitch QFP soldering, If the partical size desired is 25 to 30 μm, it should applied with less than 20 μm solder paste for an ultra fine-pitch IC.FluxFlux contains a thixotropic agent, which allows the solder paste to have pseudoplastic flow characteristics. Since the viscosity decreases when the paste passes through the stencil apertures, the paste can be applied to the PCB pads rapidly. When the external force stops, the viscosity will recover to ensure no deformation occurs.

    The flux in the solder paste should be controlled to between 8 and 15 percent. A lower flux content will result in excess amount of solder paste applied. Conversely, a high flux content will result in an insufficient amount of solder applied.2StencilThicknessA stencil that is too thick will cause a solder bridge short.

    A stencil that is too thin will cause an insufficient solder to be applied.Aperture sizeWhen the stencil aperature size is too big, a solder bridge short can occur.

    When the stencil aperature size is too small, and insufficient solder paste will be applied.Aperture shapeIt is best to use a circular-shaped stencil aperture design. Its size should be slightly smaller than the PCB pad size, preventing a bridging defect during reflow.3Printing parametersBlade Angle Speed & PressureThe blade angle affects the vertical force applied on the solder paste. If the angle is too small, the solder paste will not be squeezed into the stencil apertures. The best blade angle should be set around 45 to 60 degrees.

    A higher the printing speed means that less time will be spent in applying the solder paste through the stencil aperture surface. A higher printing speed will cause insufficient solder to be applied.

    The speed should be controlled to around 20 ~ 40 mm/s.

    When the blade pressure is too small, it will prevent the solder paste from being cleanly applied to the stencil.

    When the blade pressure is too high, it will result in more paste leakage. The blade pressure is typically set at about 5N ~ 15N / 25mm.4Printing process controlPCB moistureIf the PCB moisture is too high, the water under the solder paste will quickly evaporate, causing the solder to splash and creating solder balls.

    Dry the PCB if it was fabricated over 6 months ago. The recommended drying temperature is 125 degrees for 4 hours.Paste storageIf the solder paste is applied without a temperature recovery period, the water vapour in the surrounding environment will condense and penetrate the solder paste; this will cause the solder to splash.

    Solder paste should be stored in a refrigerator at 0 to 5 degrees.Two to fours hours before use, place the paste in a normal temperature environment.

     

     

    SMT Solder Paste printer Squeegee improving solution

     

    principle of PANASONIC-MV2V(C-F-B) component recognition (1)

    An article to let you know the principle of PANASONIC-MV2V(C/F/B) component recognition

    An article to let you know the principle of PANASONIC-MV2V(C/F/B) component recognition.

    Edited by ming Gan, please contact ming@smthelp.com for more information.

    principle of PANASONIC-MV2V(C-F-B) component recognition (1)
    principle of PANASONIC-MV2V(C-F-B) component recognition (1)
    principle of PANASONIC-MV2V(C-F-B) component recognition (2)
    principle of PANASONIC-MV2V(C-F-B) component recognition (2)
    principle of PANASONIC-MV2V(C-F-B) component recognition (3)
    principle of PANASONIC-MV2V(C-F-B) component recognition (3)
    principle of PANASONIC-MV2V(C-F-B) component recognition (4)
    principle of PANASONIC-MV2V(C-F-B) component recognition (4)
    principle of PANASONIC-MV2V(C-F-B) component recognition (5)
    principle of PANASONIC-MV2V(C-F-B) component recognition (5)

    1 program composition
    1) NC PROGRAM: Z-axis components are placed at X, Y positions at θ angle
    2) PCB PROGRAM: substrate length, width, thickness and PIN spacing
    3) ARRAY PROGRAM: Z specified components
    4) PART LIBRARY: Component Information
    5) MARK LIBRARY: tag information
    2 NC PROGRAM
    1) File name: P [0-9, A-Z, +, -,.] 2) X, Y coordinates
    3) Z No: ZA+ZB, K TYPE and Q TYPE, in single and double FEEDER at 8mm width
    The difference between K TYPE and Q TYPE: * PIN, no PIN
    * PITCH: K-21.5mm Q-20mm
    * ORG: FULL is 1, K-Z1, Q-Z2 when HALF
    FEEDER: HALF must be used when mixing single and double
    Z No: Single input K TYPE: Product number, Q TYPE: Even
    4) θ angle: θ1, θ2 two, θ3 origin return
    Θ1:0° 90° 180° 270°
    Θ2: [set angle – θ1] + correction angle Reverse time is –
    5) S&R: STEP REPEAT, PATTERN REPEAT
    On time is +
    6) NO MOUNTING: 0-normal patch, 1-non-patch
    7) SKIP BLOCK: 0 – unconditional execution, 1 to 9 – conditional jump, 7 – unconditional jump
    8) MARK: 0 – no MARK, 1 – individual MARK, 2-PCB MARK, 3-PATTERN MARK
    9) LAND TEACHING: 0-NO, 1-LAND TEACHING [Recommended for the second leg of each side] 10) BAD MARK: 0-NO, 1-BAD MARK [SENSOR] 2-BAD MARK [PCB CAMERA] 11) PROGRAM OFFSET: X=, Y=, move the first point of the patch to the camera center
    The machine automatically finds PROGRAM OFFSET
    12) Z ORG is normally 1 and Z No can be set
    * NC PROGRAM sequence
    S&R->BAD MARK->MARK/PROGRAM->ROGRAM OFFSET->MARK
    3 ARRAY PROGRAM
    1) File name: P [0-9, A-Z, +, -,.] 2) Z No: Fixed cannot be changed
    3) SHAPE CODE: shape coding [machine] 4) PARTS NAME: component name [person] 5) VACUUM OFFSET: NOZZLE↑ +, NOZZLE↓ – [-3~3mm] 6) MASTER Z No.: master, slave Z axis
    4 PCB PROGRAM
    1) File name: P [0-9, A-Z, +, -,.] 2) X: PCB length
    3) Y: PCB width
    4) T: PCB thickness [NO USED] 5) Whether the PIN is used: 0-not used, 1-automatic adjustment
    6) Hole spacing: X-10
    7) Conveyor speed: 1[H]~8[L] speed, X, Y table speed when fully automatic control
    5 MARK LIBRARY
    1) SHAPE CODE: shape coding,
    X, Y: MARK size
    PCB material: 0-copper foil, 1-solder
    PATTERN: shape
    TYPE: 0-shade, 1-binarization
    6 PARTS LIBRARY
    1) Shape coding: SHAPE CODE [, 0-9, A-Z, +, -,.] 2) Component type CLASS: 1 to 99 [1 to 19 transmission recognition, 20 to 99 reflection recognition] Reflection recognition: blue light is absorbed on the orange reflector, and the surface of the component is reflected [Figure A] By recognizing: the white light of the halogen lamp shines on the orange reflector, and the reflector reflects the light.
    Depending on the component, the edge of the component is reflected to the camera [Figure B] * High reflection recognition accuracy, high passability through recognition, LED off when used
    * For identification θ: CHIP angular deviation > 35° NG, QFP angular deviation > 25° NG
    TYPE: For component color, normal condition is 1 [black best] 3) SHUTTER [Shutter]: 0-on, 1-in [Generally open] Closed left and right to ensure component identification [Figure D] 4) Component dimensions SIZE: up, down, left, right
    Hand-drawn tape to see the reverse side of the component is the same as the camera [Figure C] 5) Component thickness THICKNESS: T-component body thickness
    6) Thickness tolerance TOL: T<1 is 20% T≥1 is 15%
    7) HEAD SPEED: 1[H]~8[L] X, Y TABLE SPEED: 1[H]~8[L] 8) NOZZLE SELECT: 1~5
    9) CAMERA: 0-S, 1-L
    10) Component feed direction FEED DIRECTION: 0 to 7, 45° interval
    11) Packing method: 0-PAPER [including 32mmPEELING] 1-EMBOSS 2-BULK
    12) PUSHPIN: 0-NO USE 1-USE only for 8mm bandwidth
    13) Number of feeds FEED COUNT: 1~4 spacing 12mm
    14) Auxiliary feed: NO USE
    15) Component error correction RECOVERY: 0-NO, 1-YES, 2- large parts are sucking
    16) CHIP STAND: 0-NO, 1-YES
    [Components stand up, thickness sensor is detected, LINE SENSOR application] 17) VACUUM OFFSET: absorbing, for components [-3mm~+3mm] 18) LEAD OUT SIZE: Up/Down Left/Right
    19) LEAD PITCH: leg spacing
    20) LEAD PITCH TOL: tube leg tolerance
    21) LEAD COUNT: Up/Down Left/Right Legs
    22) Electrode part ELECTROD: The length direction of the element is the length direction of the electrode [Fig. E] The width direction of the component is the width direction of the electrode
    23) CUT LEAD: cut tube legs SIDE: 1~4, there are cut legs on the side
    COUNT: Cut off: POSTION: Position [Figure F]

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