PCB Dry Film Photoresist: Step-by-Step Process for Perfect Circuit Boards

If you’ve ever struggled with toner transfer methods or dealt with inconsistent results using liquid photoresist, you know how frustrating PCB fabrication can be. After 15 years of working in PCB manufacturing and countless hours spent troubleshooting image transfer issues, I can tell you that switching to PCB dry film was a game-changer for my workflow.

PCB dry film photoresist has become the industry standard for transferring circuit patterns onto copper-clad boards. Whether you’re prototyping at home or running a production line, understanding how to properly use dry film will dramatically improve your circuit board quality.

In this guide, I’ll walk you through everything you need to know about PCB dry film—from selecting the right thickness to troubleshooting common problems that I’ve encountered over the years. Let’s get your boards looking professional.

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What is PCB Dry Film and Why Does It Matter?

PCB dry film is a photosensitive polymer material that comes in a three-layer sandwich structure. Unlike liquid photoresist that you brush or spray on, dry film arrives as a solid sheet that you laminate directly onto your copper-clad board using heat and pressure.

The structure consists of:

• Top layer (Mylar/Polyester film): Acts as a protective cover and oxygen barrier during exposure
• Middle layer (Photopolymer): The actual photosensitive material that reacts to UV light
• Bottom layer (Polyethylene film): A separator that you remove before lamination

When UV light hits the exposed areas of negative-type dry film (the most common type), those areas undergo polymerization and harden. The unexposed areas remain soft and wash away during development, leaving you with precise circuit patterns.

PCB Dry Film vs. Other Image Transfer Methods

I’ve tried every method out there—toner transfer, spray photoresist, even hand-painting with etch resist pens. Here’s how dry film stacks up:

Method	Resolution	Consistency	Ease of Use	Cost per Board
PCB Dry Film	50µm (excellent)	High	Medium	Low-Medium
Toner Transfer	200µm (fair)	Low	Easy	Very Low
Liquid Photoresist	75µm (good)	Medium	Difficult	Medium
Direct Laser	100µm (good)	High	Easy (expensive equipment)	High

The main advantages that sold me on dry film were the consistent thickness across the entire board and the ability to achieve fine traces down to 50µm line/space. When you’re working with QFN or TSSOP packages, that precision matters.

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Choosing the Right PCB Dry Film Thickness

Selecting the correct film thickness is one of the most overlooked aspects of the process. Most hobbyists grab whatever’s cheapest on eBay without considering how thickness affects their results.

Dry Film Thickness Selection Guide

Thickness	Best Applications	Resolution Capability	Notes
0.5 mil (15µm)	Ultra-fine line HDI	< 25µm L/S	Professional use only
0.8 mil (20µm)	Fine pitch SMD, flex boards	25-50µm L/S	Great for advanced hobbyists
1.0 mil (25µm)	General prototyping	50-75µm L/S	Most popular choice
1.2 mil (30µm)	Standard through-hole	75-100µm L/S	Good for beginners
1.5 mil (38µm)	Hole tenting, plating	100-150µm L/S	Better etch resistance
2.0 mil (50µm)	Heavy copper, thick boards	> 150µm L/S	Maximum protection

Here’s my rule of thumb: use the thinnest film that still gives you acceptable yields. Thinner film means better resolution and sharper edges, but it’s less forgiving if your surface prep isn’t perfect.

For most hobbyist work with 0.3mm pitch components, 1.0 mil film works great. If you’re doing simpler boards with 0.8mm pitch or larger, go with 1.2 mil—it’s more forgiving and easier to work with.

Read more: A Step-by-Step Introduction of PCB Manufacturing :

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Essential Materials and Equipment

Before diving into the process, let’s gather everything you need. I’ve wasted enough time running to the store mid-project to know you want this ready upfront.

Core Materials

Material	Specification	Where to Find
PCB Dry Film	Negative type, your chosen thickness	eBay, Amazon, Think&Tinker
Copper-clad board	FR-4, cleaned and degreased	Electronics suppliers
Sodium carbonate	1% solution (developer)	Supermarket (washing soda)
Sodium hydroxide	3-5% solution (stripper)	Hardware store (lye/drain cleaner)
Transparency film	Laser printer compatible	Office supply stores
Etching solution	Ferric chloride or sodium persulfate	Electronics suppliers

Equipment

• Laminator: Modified office laminator (or hot air gun/iron for DIY)
• UV exposure unit: Commercial unit, DIY LED box, or even sunlight
• Developing tray: Plastic container for sodium carbonate bath
• Soft brush or cotton swabs: For gentle agitation during development
• Sandpaper/Scotch-Brite pad: 150-400 grit for surface preparation
• Acetone: For final surface cleaning
• Yellow/amber lighting: To prevent premature exposure

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Step 1: Surface Preparation—The Most Critical Step

I can’t stress this enough: 90% of PCB dry film failures trace back to poor surface preparation. The copper surface must be absolutely clean, oxide-free, and have proper micro-roughness for the film to bond correctly.

Cleaning Process

Mechanical Cleaning: Start with 150-400 grit sandpaper or a Scotch-Brite pad. Sand in one direction initially, then cross-hatch at 90 degrees. You’re creating micro-scratches that help the film adhere—not trying to remove copper.

Chemical Cleaning: After sanding, wipe the board with acetone using a lint-free cloth. This removes oils, fingerprints, and any remaining particles. Let it evaporate completely.

Optional Acid Dip: For best results, dip the board in 10-15% sulfuric acid for 60 seconds. This removes any remaining oxide layer. Rinse with distilled water and dry immediately.

The Water Break Test: Here’s how you know the surface is ready: run water over the board. If the water sheets off evenly without beading, you’re good. If you see water droplets forming, there’s still contamination—clean again.

Pro Tip: Never touch the cleaned copper surface with bare hands. Use gloves from this point forward. Even a fingerprint will cause adhesion problems.

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Step 2: Dry Film Lamination

Lamination is where the PCB dry film bonds to your copper surface. Getting the temperature and pressure right is crucial.

Recommended Lamination Parameters

Parameter	Optimal Range	Notes
Temperature	100-125°C (212-257°F)	Varies by film brand
Speed	1-3 m/min (3-10 fpm)	Slower = better adhesion
Pressure	3-6 kg/cm²	Firm but not excessive
Environment	< 55% humidity	Affects film behavior

Lamination Process

1. Cut the dry film slightly larger than your PCB (about 5mm extra on each side)
2. Identify the layers: Use tape on both corners to separate the protective films. The shiny side (Mylar) stays on top; the matte side (PE) gets removed
3. Remove the bottom PE film: Peel slowly at a 45-degree angle to avoid stretching
4. Position and tack: Align the exposed sticky side to one edge of your copper board and tack it down
5. Remove air bubbles: Starting from the tacked edge, use a roller or credit card to press out any trapped air. Work slowly from center to edges
6. Run through laminator: Feed the board through your laminator 2-4 times, flipping between passes. Keep the Mylar layer on during lamination
7. Cool down: Let the board cool for 10-15 minutes before exposure. Never expose while warm—thermal expansion affects registration

Alternative: Water-Assisted Lamination

If you’re getting bubbles with the dry method, try the water technique:

1. Fill a tray with room-temperature distilled water
2. Submerge your clean copper board
3. Remove the PE layer from your dry film underwater
4. Float the film on the water surface
5. Lift the board at an angle, catching the film as you go
6. Squeegee out water and air bubbles
7. Dry overnight in a warm, dark place before exposure

This method gives bubble-free results almost every time, though it takes longer.

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Step 3: Creating Your Photo Tool (Artwork)

The quality of your transparency film directly affects your final board quality. I’ve seen beautiful lamination jobs ruined by poor artwork.

Artwork Requirements

• Print on laser transparency: Inkjet transparencies work poorly—the ink isn’t opaque enough
• Maximum opacity: Print at highest density settings; double-print (stack two transparencies) if needed
• Film negative: For negative dry film, your traces should be transparent (clear), and areas to be etched should be opaque (black)
• Emulsion side down: The printed (toner) side must contact the dry film directly during exposure to prevent light undercutting

Testing Opacity

Hold your printed transparency up to a bright light. If you can see light through the black areas, it’s not opaque enough. Either:

• Increase printer density
• Print two copies and align them perfectly
• Use a photopositive method with proper lithographic film

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Step 4: UV Exposure

Exposure is where your circuit pattern transfers to the dry film. The exposed areas polymerize and become resistant to the developer solution.

Exposure Parameters

Light Source	Typical Exposure Time	Distance	Notes
350-400nm UV LED array	1-3 minutes	15-30cm	Most consistent results
15W fluorescent UV	3-5 minutes	5-10cm	Common hobby choice
Sunlight (midday)	10-15 minutes	N/A	Variable, harder to control
UV nail lamp	2-4 minutes	Direct contact	Works in a pinch

Exposure Process

1. Keep the Mylar on: The top protective film blocks oxygen that would inhibit polymerization. Don’t remove it until development.
2. Ensure contact: Your artwork must be in firm contact with the dry film. Use glass plates, a vacuum frame, or bulldog clips to hold everything tight.
3. Expose correctly: Under-exposure gives soft, poorly defined traces that wash away during development. Over-exposure causes resist brittleness and makes stripping difficult.
4. Wait after exposure: Let the board rest for at least 15 minutes before developing. This allows the polymerization reaction to complete.

Determining Optimal Exposure

The best way to find your sweet spot is to run a test strip:

1. Cut a small piece of laminated board
2. Cover it with your artwork
3. Use cardboard strips to cover sections progressively (uncover new section every 30 seconds)
4. Develop and examine which exposure gave the cleanest results

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Step 5: Development

Development removes the unexposed (soft) PCB dry film, revealing the copper you want to etch. This is where your circuit pattern becomes visible.

Developer Solution Recipe

Chemical	Concentration	Temperature	Notes
Sodium carbonate (Na₂CO₃)	1% by weight (10g/L)	30-35°C (86-95°F)	Cheap and effective
Potassium carbonate (K₂CO₃)	0.85% by weight	30-35°C	Alternative to sodium

Mix 10 grams of sodium carbonate (washing soda) per liter of warm water. Fresh solution works best—don’t reuse developer that’s turned dark or has visible residue.

Development Process

1. Remove the Mylar layer: Peel off the top protective film just before developing
2. Immerse the board: Place it in the developer solution, pattern side up
3. Gentle agitation: Rock the tray or use a soft brush with minimal pressure. Never scrub—you’ll damage the resist
4. Watch for clearing: Unexposed film appears milky, then dissolves away. Development typically takes 2-5 minutes
5. Don’t over-develop: Once the copper is visible and the film is fully cleared, stop immediately
6. Rinse thoroughly: Use distilled water to stop the development process and remove any residue
7. Dry carefully: Use compressed air or let air dry. Don’t use heat at this point

Pro Tip: If your traces look fuzzy or partially developed, the issue is usually under-exposure—not development time. Check your UV source first.

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Step 6: Etching

With your PCB dry film pattern developed, you’re ready to etch away the exposed copper. The resist protects your traces while the etchant removes everything else.

Common Etching Solutions

Etchant	Concentration	Temperature	Etch Time	Pros/Cons
Ferric chloride	1:1 with water	40-50°C	5-15 min	Fast, reusable / Stains everything
Sodium persulfate	200g/L	40-50°C	10-20 min	Clean, transparent / Temperature sensitive
Cupric chloride	300g CuCl₂/L + HCl	Room temp	5-10 min	Regenerable / Complex setup

Etching Process

1. Heat your etchant to the recommended temperature
2. Immerse the board and agitate constantly—movement brings fresh etchant to the copper surface
3. Check progress every few minutes
4. Remove immediately when all unwanted copper is gone
5. Rinse thoroughly with water
6. Neutralize any remaining etchant

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Step 7: Stripping the Resist

After etching, you need to remove the remaining dry film from your traces.

Stripping Solution

Chemical	Concentration	Temperature
Sodium hydroxide (NaOH)	3-5% by weight	50-55°C (122-131°F)
Potassium hydroxide (KOH)	4-6% by weight	50-55°C

Mix 30-50 grams of sodium hydroxide per liter of water. This is caustic—wear gloves and eye protection.

Stripping Process

1. Heat the stripping solution to 50°C
2. Immerse the etched board
3. The resist will swell and peel off in sheets (usually 2-5 minutes)
4. Use gentle brushing if needed to remove stubborn areas
5. Rinse thoroughly and dry

Your board is now ready for drilling, solder mask, and component assembly.

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Troubleshooting Common PCB Dry Film Problems

Even after years of experience, problems still crop up. Here’s my troubleshooting guide based on issues I’ve actually encountered:

Air Bubbles During Lamination

Symptoms: Small voids under the film that cause pinholes in traces

Causes and Solutions:

Cause	Solution
Dirty/rough copper surface	Improve surface preparation
Film applied too quickly	Slow down, use roller method
Laminator too hot	Reduce temperature by 5-10°C
Old/dried-out film	Use fresh film stock
Humidity too low	Try water-assisted lamination

Poor Adhesion / Film Peeling

Symptoms: Dry film lifts or peels during development or etching

Causes and Solutions:

Cause	Solution
Oxide layer on copper	Add acid dip to prep, clean better
Temperature too low	Increase lamination temp to 110-115°C
Speed too fast	Reduce lamination speed
Expired dry film	Check expiration date, store properly
Residual oils/fingerprints	Never touch copper with bare hands

Under-Exposure (Soft Resist)

Symptoms: Traces wash away during development, fuzzy edges

Causes and Solutions:

Cause	Solution
Insufficient UV energy	Increase exposure time 20-50%
UV source aging	Replace tubes/LEDs
Artwork not opaque enough	Double-print transparencies
Film not in contact	Improve vacuum/contact pressure

Over-Exposure (Hard Resist)

Symptoms: Can’t develop pattern, film too brittle, hard to strip

Causes and Solutions:

Cause	Solution
Too long exposure	Reduce time, run step tests
UV source too powerful	Increase distance or add diffuser
Contaminated developer	Mix fresh solution

Incomplete Development

Symptoms: Residual film in etch areas, poor copper removal

Causes and Solutions:

Cause	Solution
Under-exposure	Increase UV time (counterintuitive but true)
Developer too weak	Check concentration (1% Na₂CO₃)
Developer too cold	Warm to 30-35°C
Development time too short	Extend by 30-60 seconds

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Best Practices for Consistent Results

Over the years, I’ve developed these habits that have made my PCB dry film process nearly foolproof:

1. Keep a process log: Record exposure times, temperatures, and results. When something works, you’ll know exactly what to repeat.
2. Test first: Always run a test exposure on scrap material before committing your actual board.
3. Control your environment: Work in amber/yellow lighting. Even brief exposure to fluorescent lights can affect uncured film.
4. Fresh chemicals: Developer and stripper degrade over time. Mix fresh solutions regularly—it’s cheap insurance.
5. Store film properly: Keep dry film sealed, away from light, at room temperature. Cold film from a fridge needs time to acclimate before use.
6. Don’t rush cooling: Let laminated boards cool completely before exposure. Thermal stress causes registration problems.
7. Use quality transparencies: Cheap transparency film often isn’t opaque enough. Invest in proper laser-compatible film.

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Useful Resources and Download Links

Here are the resources I actually use and recommend:

Technical Datasheets

• DuPont Riston Dry Film Datasheet – Industry-standard specifications
• Dynachem Laminar Processing Guide – Detailed process parameters

Suppliers

Supplier	Products	Region
Think&Tinker	DuPont Riston, chemicals	North America
Mega Electronics	Dry film, UV equipment	Europe
Various eBay/AliExpress sellers	Budget dry film rolls	Global

PCB Design Software (Free)

• KiCad – Full-featured, open-source EDA suite
• Fritzing – Good for beginners and Arduino projects
• EasyEDA – Web-based with integrated ordering

Community Forums

• EEVblog Forums – Active PCB fabrication discussions
• Instructables PCB Projects – Step-by-step tutorials

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Frequently Asked Questions About PCB Dry Film

1. How long can I store laminated boards before exposure?

Laminated boards can be stored in complete darkness for up to 2 weeks without significant degradation. I’ve successfully used boards after one month of dark storage, but fresher is always better. If storing, wrap in black plastic and keep at room temperature.

2. Can I use sunlight instead of a UV exposure unit?

Yes, though it’s harder to control. Midday sunlight in summer provides strong UV—typically 10-15 minutes of exposure works. Winter sunlight is weaker and takes longer. The main challenge is consistency; clouds and time of day dramatically affect exposure. For reliable results, invest in a UV LED array or fluorescent UV box.

3. What’s the minimum trace width achievable with PCB dry film?

With proper technique and thin (0.8 mil) film, you can reliably achieve 50µm (2 mil) traces and spaces. Professional fab houses using 0.5 mil film can go down to 25µm. For home hobbyists, 100-150µm (4-6 mil) is a realistic target. Your limiting factor is usually artwork quality, not the dry film itself.

4. Why is my developed resist sticky or tacky?

Post-development stickiness indicates incomplete polymerization—usually under-exposure. Increase your exposure time by 25-50%. A quick fix is to dip the developed board briefly in dilute acid (like white vinegar), which neutralizes alkaline residue and hardens the surface. You can also post-expose the developed board to UV for 2-3 minutes.

5. Can I reuse developer solution?

Developer loses effectiveness as it absorbs dissolved photopolymer and as the carbonate reacts with carbon dioxide from air. Fresh solution gives the most consistent results. In practice, I’ll reuse developer for 2-3 boards before mixing a fresh batch. If development times start extending or you see residue on cleared areas, it’s time for new solution. At ~$0.50 per liter, fresh developer is cheap quality insurance.

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Safety Considerations When Working with PCB Dry Film

Working with PCB dry film involves several chemicals that require proper handling. Don’t skip this section—I’ve learned some of these lessons the hard way.

Chemical Hazards

Sodium Hydroxide (Stripping Solution) This is the most dangerous chemical in the process. Even a 3% solution can cause serious burns. Always wear:

• Chemical-resistant gloves (nitrile or rubber)
• Safety glasses or goggles
• Long sleeves

If you get NaOH on your skin, rinse immediately with plenty of water for at least 15 minutes. Keep a bottle of white vinegar nearby—it can help neutralize the base in an emergency.

Ferric Chloride (Etchant) Ferric chloride isn’t as caustic as NaOH, but it permanently stains everything it touches and is corrosive to metals. Work in a well-ventilated area and keep it away from sinks with metal drains. Dispose of spent etchant at your local hazardous waste facility—never pour it down the drain.

UV Exposure Don’t look directly at UV light sources. Even brief exposure can damage your eyes. If using a DIY UV box, ensure it’s fully enclosed when operating.

Environmental Disposal

• Developer solution: Neutralize with acid (vinegar works), then dispose as normal waste
• Stripper solution: Neutralize with acid before disposal
• Ferric chloride: Take to hazardous waste collection—never drain
• Dry film waste: Regular trash is fine; it’s not hazardous once cured

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Advanced Tips for Professional Results

Once you’ve mastered the basics, here are some techniques that separate good boards from great ones:

Double-Sided Board Registration

For double-sided boards, alignment is everything. My method:

1. Drill small registration holes (1mm) in the corners before laminating
2. Use these holes to align your artwork on both sides
3. Laminate and expose one side completely
4. Flip, laminate the second side using pins through the registration holes
5. Expose the second side
6. Develop both sides simultaneously

Fine Line Resolution Tips

For traces under 150µm:

• Use thinner dry film (0.8 mil or less)
• Ensure perfect artwork contact (vacuum frame helps enormously)
• Consider collimated UV light to prevent undercutting
• Reduce development time—fine lines dissolve faster
• Use fresh, properly concentrated developer

Post-Development Hardening

For improved etch resistance, especially on complex boards:

1. After development, rinse thoroughly
2. Let the board dry completely
3. Give it a brief UV post-exposure (30 seconds to 1 minute)
4. This additional curing strengthens the resist

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Conclusion: Master Your PCB Dry Film Process

PCB dry film photoresist has transformed home circuit board fabrication from an inconsistent art into a repeatable process. With the right materials, proper surface preparation, and attention to exposure and development parameters, you can produce boards that rival professional quality.

The learning curve is steeper than toner transfer, but the results are worth it. Fine-pitch components that were impossible with other methods become routine. Yields go up, frustration goes down, and you spend less time fixing bad boards.

Start with 1.0 mil film, nail down your lamination and exposure parameters with test strips, and document everything that works. Before long, you’ll wonder why you ever bothered with toner transfer.

Got questions about your specific setup? Drop them in the comments—I’ve probably troubleshot the same issue at some point.